Open Weblink Chromosome Viewer Biology Essay


Relate the elements of the culminating assessment task rubric to oral and written descriptors identified by the students during the brainstorm. Discuss which parts of the rubric should be adapted.

Open Weblink - Chromosome viewer and read through the task, assuring students that they will soon be familiar with specific terminology (for example, chromosome, pedigree) and that this assignment requires them to personalise the effects of having a genetic disease, as well as evaluate the scientific information.

Give students time to explore the website and select a disease they would like to study. Depending on the size of the class, you may wish to assign them a number to narrow their choice to a particular chromosome.

At the end of the lesson, list the diseases students have nominated. Remind them of all the components of the task, and agree to the due date. Clarify any concerns students may have about the assignment and record a time when you plan to follow up on particular students.

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Consider this activity as a kind of pre-test. Repeat this at the end of the unit, as evidence that students have progressed.

If students already know this information, suggest extension activities or even invite them to teach parts of the unit. For example, they could develop their own animation of mitosis or meiosis - see an alternative Activity 1.4 on page 15. Much disenfranchisement and lack of engagement by students is derived from boredom because knowledge is now available everywhere (with the Internet).

For information on setting up a blog go to page xv. A glog is simply a blog with visuals or graphics. Students are to use this glog to capture their thinking, key ideas, concepts covered and things that they consider to be important.

Students will have used both Wallwisher and Timetoast in previous Nelson iScience books. Wallwisher is a free online Web 2.0 tool that enables students to build a wall where they can put sticky notes, videos, PowerPoint presentations or PDF documents. Timetoast is a free online tool that enables students to create a timeline with embedded photos and videos.

This weblink places size in perspective. Note that 'levels of complexity' are important in terms of influence, and usually do not impact more than one level above or below. For example, subatomic forces (linked to H-bonding) are very important in terms of molecular folding, and processes like adhesion and cohesion of water during transpiration, but have little influence in the interactions between organs and whole organisms.

The following links raise additional activities to explore regarding ethical issues for individuals susceptible to genetic illness.

• Are you susceptible? Weblink:

• Making decisions in the face of uncertainty:

This is a simple animation to consolidate student understanding of the complementary base pairing rule.

• Dishwashing liquid: Palmolive dishwashing liquid is recommended. Shampoo will also work. Use about 1 tablespoon

• Buffer: This can be kitchen salt, although 8.8g NaCl and 44g Sodium Citrate per litre of water is recommended. Use enough to moisten the material.

• Filters: Coffee filters work well.

• Meat tenderiser: Masterfoods works well. Some recipes suggest 1 tablespoon/extraction.

• Option: Some investigations recommend staining the DNA with methylene blue.

Student responses will vary.

Student responses will vary. The purpose of each step is listed in the method.

Yes. Factors to consider: surface area exposed, amount of liquid in the original tissue (why wheat germ is such a good, concentrated source).

Excellent quality answers will discuss the mechanisms of how detergents work - formation of micelles, and recognition that cell membranes contain lipids. Adequate answers repeat information provided in the method.

Alcohol is less dense, therefore adding it carefully demonstrates this; adding it without care still precipitates the DNA, but the solution may look cloudy and it will be hard to lift out.

Differences could arise because there could be technical issues (spillage) or some materials (particularly watery fruit) may have proportionally less DNA.

The important aspect is that students demonstrate efforts of reflection to obtain their answer, even though it is likely to be an over estimate, since the 'DNA' they extracted is mostly histone (Refer to Fig 1.9 on page 12).

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50Ã-1000000Ã-3Ã-21 meals=3.15Ã-109 or 3150000000km.

It is related to the way DNA is isolated from the rest of the cell - about its acid nature - and how it is already surrounded by special proteins.

The use of the buffer compacts the DNA, which is then precipitated. The extracted 'DNA' is not a single strand, and a lot of it is histone.

We can discover the presence of DNA nucleotides using a process of gel electrophoresis. Easy and cheap demonstrations of the process can be found at and

This is a YouTube video that runs for 2.53 minutes. It is an excerpt of an interview with Richard Dawkins. Students could watch this video for homework and answer the following questions.

• What discovery in physics does Dawkins think is one of the greatest scientific discoveries?

• What are the consequences of the discovery of the double helix molecule?

• How is a chromosome similar to a computer program?

This is a simple description of the chemistry of this molecule.

You may wish to expand some features; for example: what makes DNA a polymer? Why DNA is a 'digital code'? Why does the molecule have a helical shape?

Students have difficulty picturing how the arrangement of dots in the X-ray photograph translates to a spiral. Draw a spiral using indelible marker on an empty plastic soft drink bottle, and mark the nucleotides using circular stickers (or drawing large dots). There should be approximately 10 nucleotides per 360° turn, and of course the dots need to be placed in opposing pairs.

Cut of the ends of the bottle, and ask students to look down it. Note how only one position provides this 'image' - a tribute to Franklin's technique and care.

The 1987 film Double Helix with Jeff Goldblum is a good biographical account of the story behind the science. The script was written by James Watson and it is interesting to see how Watson viewed Rosalind Franklin.

Interesting books for teachers and students about Franklin and how Nobel Prizes are awarded include:

• Anne Sayre. (1975). Rosalind Franklin and DNA, Norton paperback

• Brenda Maddox. (2003). Rosalind Franklin: The dark lady of DNA, Harper Collins

• Sam Kean. (2010). The Disappearing Spoon and other tales of madness, love and the history of the world from the Periodic Table of the Elements, Hatchette Book Group.

Genetics is the study of heredity.

Deoxyribonucleic acid

A nucleotide

A sugar, a phosphate and a (nucleic acid) base

A double helix (two twisted spiral strands)

Adenine only pairs with Thymine; Guanine only pairs with Cytosine.


Franklin was notorious for not being careful near X-rays, even as the dangers were becoming known (refer to Nelson iScience 9 Unit 2). Yet it would always be difficult to prove this was the cause of her cancer.

Student responses will vary. An important consideration is whether we should we judge actions of the past with the ethics we are familiar with today (even when this history is relatively recent)? Franklin's own reaction to the Watson-Crick model is reputed to have been delight; she felt it didn't matter how the problem was solved, only that it was more important that it was solved.

Student responses will vary. Many scientific discovers are likely to be the work of more than one person, over time. Had Franklin lived, she may have been eligible for the Nobel Prize in a different category (see More information: Rosalind Franklin box on page 6).

A simple animation from Education Services Australia to provide students with practice matching nucleotides. This is called semi-conservative replication, because the original DNA forms half of each new DNA strand.

This is a 49 second YouTube video that clearly shows how DNA is replicated.

An interactive from Education Services Australia gives an explanation about the transcription and translation of DNA to proteins.

This video runs for 2 minutes and provides a clear animation of the process of translation. It starts with the mRNA leaving the cell and moving to a ribosome where the protein chain is formed. It looks at the role of tRNA in transporting the amino acids. A full transcript of the video is provided.

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An insight into the spirit of scientific research during the mid-20th century is how the 'RNA Tie Club' was formed to collaborate on the problem of protein synthesis. The selected scientists - all male - were each assigned the name of an amino acid; for example, Watson was proline and Crick was tyrosine. By synthesising ideas from a very wide range of scientific papers, and connecting evidence from many unrelated experiments (called inter-field research), the select group hypothesised the following was needed for protein synthesis.

• A messenger molecule was needed to export DNA information from the nucleus.

• A second type of molecule was needed to capture amino acids in the cytoplasm.

• A special structure in the cytoplasm was probably required for protein assembly, acting like a workbench.

Discuss (think/pair/share) with students the following questions.

• Which biomolecules and structures match the RNA Tie Club's theoretical proposals?

• How important is it for scientific research to be available to the entire scientific community? (What if the research can potentially be used for harm; for example, to develop bio weapons?)

Scans of original letters from Crick, including notes to the RNA Tie Club members, can be found at

An excellent assortment of information (including interactive problems and student worksheets) on protein synthesis and gene technology can be found at the following site. Walter & Eliza Institute Gene Technology Access Centre (GTAC):

ICT capability; Critical and creative thinking; Personal and social capability


This is a cooperative learning strategy which develops the thinking of all students by breaking down interaction and discussion into pairs. This means all students, including those with English as a second language/dialect, will be heard, at least by a peer. Conclude the activity by having groups summarise their ideas with the whole class.

This is a fun activity that requires students to translate their own name into three-letter DNA code and then using this code, make a bracelet using four different coloured beads. For this activity you will need coloured beads (green, red, blue and black), hat elastic (needs to be able to fit through the hole in the bead) and scissors.

The aim of the activity is to reinforce with students that the genetic code is a three-letter sequence that codes for amino acids, and that it is the sequence of amino acids that is important when making the protein.

The process of semi-conservative replication involves the DNA molecule splitting, having a new a complementary strand made using the original as a template. The outcome is that the two copies are genetically identical.

Name of the molecule

Where does the activity take place?

What is the name of the process?

DNA (triplet)



mRNA (codon)



tRNA (anticodon)


Protein synthesis

To extend students with this question, they could name units on DNA molecules, and for protein synthesis, discuss peptide bonding.


Tyr - Asn - Pro - Arg - Phe - STOP

One possibility is: UUG CCU AAU GAU CGU

6 (Leu codons)

Ã-4 (Pro codons)

Ã-2 (Asn codons)

Ã-2 (Asp codons)

Ã-4 (Arg codons)



Tyr - Glu - His - Tyr - Gly - Met - His - His - STOP

It would change the sequence of amino acids in the protein and therefore make a different protein. CGG codes for Arginine whereas CAG codes for Glutamine.

Tyr - Arg - His - Tyr - Gly - Met - His - His - STOP

It would mean that this protein would be different and could not be used for the function it was meant to be used, or it could be used differently. For example, if the protein was an enzyme then the chemical reaction may no longer occur.

Student responses will vary, but students should understand that some effects of DNA error can be serious.

Table 1.1 reveals the third letter is often much less important to the identity of an amino acid than the first or second. Therefore, some changes in the DNA will not change the protein. Replacement amino acids can have a variable affect. If they are chemically similar to the original, so that the protein folds nearly the same way, or they are in an unimportant position in the polymer, the mutations may make very little difference to the organism. Occasionally, a crucial amino acid is replaced. Several genetic diseases including haemophilia (a blood clotting disorder) and achondroplasia (a type of dwarfism) are caused by faulty proteins with this type of error. Deletions or additions are examples of 'phase shift' mutations. Adding or deleting one or two base pairs affects all the triplets in the gene, and therefore all the amino acids in the protein (if the molecule can be transcribed at all). A deletion or addition involving three base pairs (or a multiple of three) enables the most of the DNA to be translated correctly, with a missing or extra amino acid(s). Cystic fibrosis is an example of a genetic disease caused by a triplet deletion, and several very serious neurological conditions, including Huntington's disease, are caused by extra repeats of DNA triplets.

Amino Acid Explorer compares characteristics of amino acids and how often they can be substituted:

When observing prepared slides of onion root tips, remind students of the correct procedure for focusing a microscope at high power.

• Remind students to start with the smallest objective lens, close to the slide.

• Use the course focus to drop the stage away until the object is in focus.

• Use the fine focus to fine tune.

• If increased magnification is desired, move to the next size of objective lens, use fine focus, and so on, progressively.

Giving attention to the correct procedure will ensure microscope lenses remain unscratched and the instruments serve the school for many years.

It can be very exciting to prepare your own onion root tips for examination, growing the bulbs in cool conditions. Because cell divisions often occur at about noon, 'stopping' the roots at this time is likely to provide the best results.

Safety note: students should not be involved in 'stopping' the root tips (steps 1-3), because of the chemicals involved, but may enjoy watching the process being demonstrated over the week leading up to the lesson.

Fix the roots in acetic acid (a fixative made by 1 part glacial acetic acid and 3 parts absolute ethanol; it should be mixed just before using), changing the solution once.

Stand for 1-2 days.

Replace the fixative with 70% ethanol, changing the solution twice. The root tips can be stored in a refrigerator for months like this.

Safety note: take care near steam! The stain is also corrosive; therefore these slides themselves are best completed as a teacher demonstration.

Prepare squash preparations using aceto-orcein stain (1g aceto-orcein in 45% acetic acid solution).

Use a root tip about 2-3mm from the end of the root.

Mash the root tip on the slide, adding a drop or two of stain, until there are no lumps.

Add a cover slip, and carefully tamp it down over the cell suspension.

Warm the slide over a steam bath (a hot plate, sometimes recommended, can destroy the tissue) and when the liquid near the edges of the cover slip starts drying off, press the slide between paper towels.

Optional: edges may be sealed with nail polish, making lightly longer lasting slides.

Students should be able to work with this 'wet mount' for about 30 minutes.

This video runs for one and a half minutes. It provides an excellent animation of how DNA is tightly packed so that two metres of DNA can fit into a space as small as a nucleus in a cell. A full transcript of the video is provided.

Make sure you play the video through first before you show it in class as it takes a while to download.

Good slide shows can be found on

ICT capability; Critical and creative thinking

This is a YouTube video that runs for 1.49 minutes. It clearly shows the process of meiosis using a cell 2n=6.

Allow students to be creative in the way that they represent meiosis. Upload the final creation to the class wiki and allow students to see what other people have done, and to comment on them.

As one option, some students may choose to produce a claymation of meiosis which they could then photograph.

Use coloured plasticine to model and represent events during cell division.

Photograph your plasticine model/s, as you move the pieces in small steps.

Organise your photographs into Microsoft Moviemaker or similar software.

Upload your creation to the class wiki.

Students will understand that there is a lot of DNA inside a cell nucleus. When a whole lot of threads are jumbled together, inevitably some get tangled. This is what occurs in crossing over. The arms of the chromosomes become tangled and break, switching places with their counterpart on the other homologue. Crossing over is more likely to happen in the longer chromosomes than the shorter one (tangling more often occurs in a longer piece of string than a short piece of string).

Remind students that laboratory organisms are chosen for their useful features - notice the transparency of the sea urchin egg, and the effects of fertilisation on opacity.

X only

X or Y





Coin toss outcomes will vary.

Student responses will vary - some will have the same ratio.

No, they should not, as these are independent events.

Yes, the resulting ration is likely to approach 50:50.

By chance, every time they have a child it could be the same sex.

This activity aims to highlight the importance of chance in determining ratios. Sometimes students assume that because they understand how the Mendelian ratio comes about, any family with four children therefore should express the full range of possible outcomes. However, by chance, all four children may be homozygous recessive. Genes or chromosomes, they both segregate randomly.

Student responses will vary.

The following are suggested answers only.

Answers could include the couple's satisfaction to have the desired family format. However, there could be risks - some sexes are more prone to genetic disease.

Medium consequences - if the choice results in an imbalance of sexes (such as has occurred in China and India in the last few decades), the majority sex may have difficulty with dating or finding a partner.

Some human societies practice polygamy (multiple wives) and, more rarely, polyandry (multiple husbands). In some cases these traditions have come about because of very different sex ratios or wealth distribution.

Student responses will vary.

This task can be completed as a claymation in a single long(ish) lesson. Students could use their phone cameras or a flip phone.

Genes are on the chromosomes (Figure 1.9); Chromosomes are in the nucleus (Figure 1.8).

Chromosomes come from our parents. Each of their sex cells (sperm or egg) would have half the chromosomes in their own cells.





Half: 26




50% or 0.5 or 1/2

50% or 0.5 or 1/2


There are two combinations. Boy then girl =1/2Ã-1/2=1/4 or, girl then boy =1/4 Add the two possibilities together: 1/4+1/4=1/2


There should be none


The genetic information is halved in gametes (haploid); fertilisation restores the normal amount (diploid).

No, because of random assortment (maternal and paternal chromosomes being sorted differently, randomly, and because of crossing over during prophase).

This is metaphase - showing the chromosomes on the centre plate. It is probably during mitosis - no evidence of homologues paired up (therefore, not metaphase I, meiosis), or that a nearby cell is also undergoing metaphase (therefore not metaphase II, meiosis).



What happens to the number of chromosomes?

Exactly the same


How many cell divisions are involved?



How many daughter cells are produced?



What is the purpose of this kind of division?

To keep the information identical -e.g. in growth and repair, in asexual reproduction (binary fission)

To halve the information in the sex cells

Identical twins form from a fertilised egg dividing by mitosis. Therefore, the chromosomes in their nuclei are exactly the same.

No, because sex is genetically determined.

One consequence is that there is less variation in the offspring, because siblings share, on average, half their DNA. The outcome is that recessive genes (see section on Pedigrees on page 28) are also likely to be shared. This increases the chance that offspring will have two copies of these recessive genes, which is a problem if the genes are damaging.

PMI is an abbreviation for Plus, Minus, Interesting. These are suggestions only, as this is open ended.

Plus: offspring have variability.

Minus: some offspring have disadvantageous genotypes.

Interesting: Courtship behaviour and displays would not exist without sexual reproduction.

Examples of answers (pre-evolutionary thinking, anticipating Unit 2) below.

• If poorly adapted organisms are produced, these will be disadvantaged if a resource becomes critical (and therefore they may not get to reproduce themselves).

• If well-adapted organisms are produced, they will be able to take advantage of resources better than others.

Brainstorming: responses will vary. Note: it is only vital if environments change. There are many organisms - for example, extremophyles, prokaryotes, that seem to have changed little in the past 3.8 billion years. This is because they survive in conditions suspected to resemble those of the early Earth - for example, hot springs, black smokers in ocean depths.

There is evidence for all three hypotheses, and there are several others, also with evidence.

For example, organisms (often, plants) with fewer sexual cycles are more susceptible to parasitic infections. This explanation is favoured by ecologists, because the reproductive mode is often aligned with seasonal changes. (example: aphids reproduce sexually before winter, and asexually in spring.)

Inefficient mutations can be removed by selection in asexual organisms. But this does take longer than being infertile or not having a chance to reproduce in sexual organisms. It is particularly fast in species with haploid sexes, like bees. This explanation is favoured by geneticists.

The organelle hypothesis is the most recent, because it requires sophisticated cytology. It now seems an ovum (the source of all the mitochondria in every body cell) is likely to start with as few as 12 mitochondria. This explanation is favoured by cytologists.

If students are to express opinions, they need to back it up with some wider reading. In addition, all the mechanisms can occur in combination, in all organisms.

This website provides information on the hallmarks of cancer, causes and prevention, diagnosis and treatment, and pathways to cancer. Information is provided in the form of animations, video or slides.

This 30-second YouTube video looks at point mutations and chromosomal mutations. Students could watch it for homework and then provide a definition of each type of mutation.

A mutation is a change in DNA.

Changes can result from environmental factors, including radiation (UV, X-rays and gamma rays) and harmful chemicals. Changes can also occur from copying error during mitosis and meiosis. (Estimated on average, to be 5 point mutations in 3 billion per mitotic cycle in human cells.)

DNA mutations can result in (i) no changes in the protein, because the amino acid it codes for is the same; (ii) no effect, because it does not disadvantage the organism in any way; (iii) harmful effects, because the change damages a vital protein or causes cancer.

'Silent' mutations are changes in DNA that do not change the protein. This is because the majority of amino acids can be translated from more than one sequence of three base pairs (DNA triplet).

DNA mutation rates can be increased by exposure to radiation - particularly UV and X-rays, or mutagenic chemicals.

Student responses will vary, and will draw on information on page 21.

Student responses will vary, but students may realise appearances (such as age spots) sometimes do not matter, if the effect is not harmful or disadvantages the organism.

Replicates increase the statistical probability that the results match the average of the general population. For example, if Mendel tested only the outcomes in four offspring, it is possible that the ratio would be wildly different from the 3:1 ratio he observed.

In the F2, all the results are in a 3:1 ratio.

This clip shows a re-enactment of Mendel at work, clearly explaining the process of cross-fertilisation in Pisum sativum.

This weblink,, leads to an excellent free resource for students and teachers. It can be downloaded free in iTunes and the App store. Students will learn about inheritance of recessive gene traits and diseases, and will develop an understanding of how some populations suffer from certain diseases more frequently than other populations. It features animations, Punnett square calculators and other useful features.

This activity is designed to show students that a knowledge of genetics can be valuable in a variety of career choices. Xtranormal requires students to sign up, and it turns words into 3D animated movies. An alternative could be to use a voki (

Translations of Mendel's original 1865 scientific paper can be found on and Mendel's own explanation for the 3:1 ratio appears on page 25.

Guiding question for a class discussion: is scientific integrity always under question?

Mendel's work is rich terrain for discussion about scientific integrity, academic honesty and the nature of science. A famous 1936 statistical analysis of Mendel's results, by Ronald. A. Fisher* gave χ2 results that suggested Mendel's data were in fact, highly improbable.

Were his results falsified or an example of 'confirmation error' leading to biased collecting of a suspected outcome?

An alternative explanation that Mendel's results were a natural consequence of pollen meiosis producing 'tetrads' that resulted in Mendelian ratios are also disputed:

For kinesthetic learners, consider enacting this in the school grounds (for example, basket ball court, marked out with chalk) in which pairs of students act as 'paired alleles' or 'X/Y chromosomes'. When pairs match up in the squares, decide on the phenotype.

RR Ã- rr F1 = Rr F2 = 1RR : 2Rr : 1rr (phenotypes 3 red : 1 white)

Rr Ã- rr

F1 = 1Rr : 1rr (phenotypes 1 red : 1 white)

Ww Ã- Ww

F1 = 1WW : 2Ww : 1ww (phenotypes 3 long-winged : 1 short-winged)

Rr : rr in 1 : 1 ratio (2/4 round : 2/4 wrinkled)

GG : Gg in 1 : 1 ratio but all will look dark green (2/4 : 2/4)

yy : Yy in 1 : 1 ratio (2/4 bright green : 2/4 yellow)

100% Yy - heterozygous yellow (4/4)

(*Hint: suggest a symbol for this trait)

Example: TT Ã- tt 100% Tt - heterozygous tall (4/4)

The outcome becomes like a backcross: Tt : tt in 1:1 ratio (2/4 tall : 2/4 short)

This phenotype requires two recessive types of information.

The correct ratios are: 1 : 2 : 1 + 3: 1 + 1: 1 + 1

The ratio can be expanded and then add up to 1 (that is, all the offspring)

Example: 1 : 2 : 1 =1/4+2/4+1/4=1

3 : 1 =3/4+1/4=1

1 : 1 =2:2=2/4+2/4=1

1 =4/4




Not needing oxygen or air


Without (oxygen)


Ancient (organism)


Self (nutrition)


Life (living) chemistry


Life (living) diversity


Green leaf


Cell (division)


Inside symbiosis


Birth/origin (of)


Different nutrition


Different (from zygote)


Same study of


Same (from zygote)


Someone who studies old things


Light making


Many (parts)


Many forms


Together life/living


Three phosphates



The study of genes


An instrument to look at tiny things


Something that can kill bacteria


A blood protein


An illness involving the stomach


Student responses will vary.

Allele - different form of a gene

Homozygous - both alleles the same

Heterozygous - the alleles are different

Pure-breeding - offspring of every generation are the same for a particular trait, this indicates the trait has homozygous alleles

Phenotype - the appearance of an organism

Genotype - the genetic composition of an organism

Any three of the following (i) Round seed form; (ii) Yellow/orange seed colour; (iii) brown seed coat; (iv) inflated ripe pods; (v) dark green unripe pods; (vi) flowers along stem; (vii) tall stems. These traits are all dominant because they were three times as common in the F2 generation.

Reginald Punnett was a geneticist who devised the 'Punnett square' method for determining the ratio of genotypes in offspring.

Let the genotype of the homozygous woman be WW; she can only provide gametes with the W allele. The genotype of the heterozygous father is Ww; half his gametes will have the w allele, and therefore half of his children will be heterozygous for widows peak.

Autosomal means the gene is found on an autosome, not a sex chromosome. Dominant means that a single copy of the gene will affect the phenotype: all carriers will eventually develop Huntington's disease.

Let the allele causing Huntigton's be H, and normal alleles be h. In the Punnett square below, the shaded squares (50%) indicate the probability the child has the condition.

Alleles in gametes of heterozygous individual



Alleles in gametes of unaffected individual







Refer to the Punnett square below.

Alleles in gametes of heterozygous wavy individual



Alleles in gametes of heterozygous wavy individual



Curly phenotype


Wavy phenotype



Wavy phenotype


straight phenotype

If each trait is considered a single variable, this is good scientific methodology, as it enables effects to be observed separately. Later, Mendel did investigate pairs of traits, and discovered they behaved independently (an effect caused by six of the traits being on separate chromosomes, therefore he was in fact observing random assortment, but did not know it).





Four genotypes: C+C+, C+cch, C+ch, C+c

Three genotypes: cch cch, cchch, cchc

Two genetotypes: ch ch, ch c

One geneotype: cc

The rule is: number of alleles - number of alleles that are dominant to the recessive phenotype.

Chromosomes are independently assorted during meiosis; therefore, Mendel's observations are essentially of independent assortment. The two genes that are on the same chromosome where highly likely to have a crossing over occurring between them, therefore behaved as if they were being randomly assorted.

If the genes were all one chromosome, the traits would often be inherited together, depending on whether there were on parts of the chromatids being exchanged. However, if Mendel analysed the genetic ratios for each trait individually, he would still have established the same 3:1 ratio for each one.

Student responses will vary.

This activity sheet should be used as extension material.




There are black hairs sprinkled through the red coat of a AyAt dog.


Yes. Students may like to reflect on the motto of a dog obedience school: It is the deed, not the breed, that counts.

All the alleles are homozygous. For example, black and tan is common and this is homozygous. Brown dogs are considered undesirable, and b is a rare allele.

The suggestion in the table is that it is a dominant gene. This could be tested by breeding dogs with and without the feature, and observe phenotypes of offspring.

Note that the frequency of the mark does not prove its dominance - O blood group in humans is the most common and it is a recessive phenotype.

German shepherds, kelpies, any breed which normally has a black saddle

50% chance each animal a carrier - therefore a 25% (0.5Ã-0.5) the cross is like an F1 cross.

25% of random matings will produce 25% affected homozygous recessive puppies.

You can get dogs genetically tested (students may not be aware of this). You can ensure you breed from dogs that have no evidence of the disease in their ancestors (they may still be carriers). You can also monitor the health of puppies - one puppy with the trait is evidence that both parents were carriers, therefore never breed from them again. You can ensure only to breed from older animals that have had eye checks. This will eliminate homozygous animals, certain to pass on the disease.

Merle is a lethal recessive - the Merle animals are all Mm. Solid coloured puppies are MM. Puppies homozygous mm are miscarried. Students may be able to show this with a Punnett square.

An outstanding, differentiated resource that uses ICT as the learning platform is GENIQUEST. Further information can be found on and the programme can be downloaded from

At the lowest level (appropriate for Year 10), students manipulate the genes on a karyotype and instantly a small dragon changes its phenotype. As students explore the possibilities, the effects of sex-linkage, lethal recessive genes, epitasis (genes influencing the expression of others) are revealed. At higher levels enable students to explore contemporary science methods, such as determining loci on chromosomes.

Hh. This is an autosomal dominant gene, therefore every carrier must have one copy. His father is homozygous recessive (hh).

hh. This individual does not express the phenotype, which is dominant.

Individual II1 is hh; her husband is hh. None of their children will be affected (shaded boxes).

Gametes produced by II1



Gametes produced by unaffected man







Here is an example of how an extension of II1 might be shown, if the couple had two sons.

I1= homozygous recessive (see key) I2 = has at least one dominant allele -homozygous dominant or heterozygous.

II1= must be heterozygous, because of his affected daughter); II2, II3, II4 and II5 must all be heterozygous, because their mother is homozygous recessive.

III1= homozygous (see key); III2, III3, III4 all have at least one dominant allele.

Haemophilia is a recessive allele because the disease is only apparent in homozygous sufferers.

Individual III2 has a 2/3% chance of being a carrier, as both parents were heterozygous (explanation: Mendelian ratio shows 2/3 of the dominant phenotypes must be heterozygous.)

If III2 is homozygous dominant, all offspring from the union will have at least one dominant allele, and therefore there is zero chance the first born, or any of his children, have sickle cell.

If III2 is heterozygous, the child has a 25% chance of having Sickle cell (see shaded box in Punnett square.

Gametes produced by III2 if he is heterozygous



Gametes produced by heterozygous woman







Combining the probabilities discussed:

(Probability III2 is heterozygous =2/3) Ã- (Probability child is homozygous =¼)


In this suggested example (section shown), IV1 is a daughter without sickle cell anemia.

I1 is homozygous XhXh. (Let us allow for the miracle of modern medicine and she survives multiple deliveries of babies.) I2 is a normal XY male.

All the mother's gametes carry the haemophilia allele on the Xh.

II1, II3 are heterozygous daughters XhX, the normal X chromosome coming from the father.

II2, II4 are haemophiliac sons XhY, the Y chromosome coming from the father.

Every son produced by the parents will be a haemophiliac, as both the mother's X chromosomes carry the haemophilia allele.

Gametes produced by II3



Gametes produced by normal male



25% haemophilic son


25% normal son



25% carrier daughter


25% normal daughter

The Pedigree can be extended as follows (the example given is the normal son).

This is a simple animation to show students how to construct a pedigree using the accepted symbols.

This video shows how much genetic siblings (fraternal twins) can vary, even in their racial appearance.

An extensive resource 'The new Genetics' available through the national Institute of Medical Sciences, incorporates detail on genetic testing and genetic engineering. It can be downloaded from

Ethical behaviour

This is a self-assessment for students to gauge their progress since commencing the unit.

Karyograms are developed from cell squashes, usually taken at metaphase during mitosis, therefore the chromosomes are mixed, as shown in the worksheet. This simple simulation provides students with experience in matching homologous chromosomes.

This is a formative task that personalises learning by being open-ended. Sharing the task on the class wiki makes the information available to all.

Person X is male.

47 chromosomes. XXY

Student responses will vary. Negative: risk of spontaneous abortion, false negatives (and positives); Positive: emotional distress of having a severely disabled child, possibly with a fatal genetic disease that causes pain and suffering.

To stop fruits from over ripening (banana), protection from fungal rot (banana) and to make fish grow bigger.

Some genes can be found naturally in the organism but are switched off, or they can come from other unrelated organisms such as radishes, onion or salmon.

Responses will vary but students should understand that every domestic crop or animal is the product of 'human interference' with nature.

Genetic modification is changing the genome of the organism by introducing genes from species that are very different (related remotely genetically). For example, a bacterium has been engineered to produce human insulin, to help diabetics. Hybridisation and selection works with the genes that occur naturally within the organism.

A website previously mentioned is

Walter & Eliza Institute Gene Technology Access Centre (GTAC): At this site are excellent PowerPoint presentations and interactive problems, teacher notes and student worksheets, including on protein synthesis and gene technology.

To understand how our body works, how illness can be overcome and how to produce better and more tailored drugs.

Currently, medical information is private because it could be misused to disadvantage individuals. It may not be in the interests of individuals to know their 'genetic future' if it predicts painful, chronic disease or low life expectancy.

Ethical issues: if commercial companies are able to select whom they will insure (inevitably those deemed at lowest risk), this does not spread the risk or benefits through the entire population (which is the fairer manner to support a community). Because genetic illness is never a choice, this type of discrimination counters 'human rights'; it is in the same category as discriminating against a person because of sex or race (which likewise, are genetically determined).

Students may argue for alternative answers: the right of a company to be profitable, for example. Observe that national insurance schemes replace private schemes in some countries.

Student responses will vary.

Benefit to company X: it has an exclusive service for all patients with this type of cancer, and this is potentially profitable. Without competition, the company can set its charges. The company may argue its monopoly provides quality assurance.

By limiting access to its scientific data, the company's 'intellectual property' is effectively quarantined, hampering the development of improved, alternative tests for the same allele.

Something else. (Extension: intermediate dominance would be expected to give plants of average height, like the wavy hair example in What have you learnt? 1.5 (Question 5). Co-dominance reveals both alleles (and example is AB blood groups), but short alleles are not apparent. This is a phenomenon called 'hybrid vigour', and is often used in agriculture to boost yields. The effect in pea plants is so small that it is often overlooked and given as a simple Mendelian ratio.

Sex-linkage (X-linkage): when the gene is on the X-chromosome.

Pedigrees show births (order, sex and number), deaths and marriages, and phenotypic patterns, from which genotypic causes can sometimes be inferred.

Student responses will vary.

The child is male and has 46 chromosomes.

I2; III1; III5

Recessive. The condition ' skips' a generation, as you would expect when the phenotype of heterozygotes does not show the allele.

Sex-linked. All the individuals with the condition are male.

I1 XHXh (heterozygous female) ; I2 XhY (haemophiliac male)

II1, II4, II5 XHY (normal males); II2, II3 XHXh (heterozygous females); II6, II7 XHX? (normal females, homozygous or heterozygous)

III1, III5 XhY (haemophiliac males); III2, III9 XHY (normal males); III3, III4, III6, III7, III8 (normal females, homozygous XHXH or heterozygous XHXh).

Affected males (XhY) will always have carrier (heterozygous XHXh) daughters.

There are no affected females, but a similar proportion are carriers (that is, 3 affected males, 4 normal males - roughly 50:50 and 5 definite carrier females and 5 who could be carriers - roughly 50:50).

Student responses will vary. Advantage: solving crime, connecting people to families (for example, adoptees, refugees, people who have amnesia). Disadvantage: privacy issues - particularly if exploited for commercial gain, enabling life insurance companies to 'cherry pick' individuals unlikely to be at risk for common diseases.

Responses will vary, though students should be developing a growing understanding of the complexity of genetic influence.

Learn more about the human genome through the following links.

• Part 1:

• Part 2:

• What is the Human Genome Project? Weblink:

• 'Your Genes Your Choices - exploring the issues of genetics research' by Catherine Baker (1995) is an AAAS resource rich in stories and issues to discuss with students:

• Understanding the Human Genome Project (The National Human Genome Research Institute): offers multiple videos, fact sheets and educational resources.

Assess this task as a gallery walk with half the class displaying and their peers using the cumulative assessment task rubric to grade them. Then reverse the roles.

Peer marking helps students reference their work to the criteria, supporting development of their skills rather than focusing on an arbitrary percentage outcome.

Student responses will vary.

Self fertilisation. This meant lines naturally became 'pure'. Mendel was also lucky the traits he chose to study were mostly on different chromosomes, sorted independently.

Transparent eggs

Transcription: the DNA information is copied using a different type of base (DNA base sequence replaced with RNA base sequence - essentially the same form, so you can ' read' it back to the original sequence). Translation: the RNA information is changed into a protein (RNA base sequence converted to an amino acid sequence - but the 'mode' has changed, therefore it cannot to used to find the original sequence).

Here is a simple version (P = phosphate group, S = Deoxyribose sugar, B = Base). The diagram should show alternating phosphates and sugar (deoxyribose). If drawing the complimentary strand, students may want to describe the A-T and C-G relationship too.

DNA: the chemical (polymer) making up the gene

Nucleotide: a unit of the DNA (polymer)

Base: the type of subunit in a nucleotide (such as A - adenine, T - thymine, C - cytosine, G - guanine)

Gene: section of chromosome that codes for a protein

Chromosome: length of DNA within cell nucleus.

Anaphase I and II are both parts of the double cell division in meiosis.

Anaphase I: the homologous pairs of chromosomes are separated (so the 2 daughter cells are haploid - each homologue consisting of 2 sister chromatids.). Random assortment.

Anaphase II: the sister chromatids of each chromosome is separated.

Crossing two heterozygote plants should result in a Mendelian ratio in the F1: 25% homozygous dominant, 50% heterozygous (phenotypically the same as the homozygous dominant plant); 25% homozygous recessive.

Diploid: 28Ã-2=56; Triploid: 28Ã-3=84

Let the son's genotype be SS and his wife's ss. All their children will be heterozygous Ss (carriers). Their fourth child would be heterozygous, but not a sufferer of sickle cell anaemia.

All their children would be carriers (see Punnett square below).

Gametes produced by son



Gametes produced wife (homozygous recessive)







This is an example of a backcross or test cross, normally done with animals/plants to find out whether a dominant phenotype carries a recessive gene. 50% of the offspring (children, in this case) will be homozygous and therefore suffer sickle cell anaemia. These have been shaded.

Gametes produced by son of couple



Gametes produced wife (homozygous recessive)







They would have 63 chromosomes - one of them would be unpaired during meiosis.

Maybe the mother's physical size, determine the size of the foetus, a horse womb being able to support a larger foetus. The preference could also be caused by animal behaviour - female donkeys are much less likely to mate with a stallion than a mare with a male donkey; therefore, hybrids with donkey mothers are much rarer. In some species, for some genes, the sex the genes originate from has an influence (this type of environmental influence on how genes are translated - in this case the maternal environment - is called an epigenic effect).

Genes on the X-chromosome in males are unmatched (because the Y chromosome in humans is much smaller) and therefore defective alleles are exposed in the phenotype. Two X-chromosomes in females gives them an 'insurance copy', which is often a dominant allele that masks genetic disease.

Males with alleles causing genetic disease are disadvantaged, but 'alleles' causing 'superior' phenotypes could give them an advantage. (Advice: There is a hypothesis many genes for intelligence are found on the X-chromosome, and this explains both the prevalence of learning difficulties and exceptional genius (people at the level of an Einstein, or Stephen Hawking) in human males. What do students think of this hypothesis, or could there be other societal factors involved?)

Student responses will vary.

Only the healthiest drones will have the strength to mate with the queen, therefore damaged genes are being removed from the population by selection.

This means the environment has an influence on gene expression - whether the gene is translated into a protein (this is called an epigenetic effect).

16:5 can be interpreted as approximately a 3:1 ratio (the Mendelian ratio) or a 2:1 ratio in which one of the possible phenotypes is missing (because the total numbers are small, there can be a large drift from the expected ratio - this is called a stochastic effect in genetics).

Therefore, test each hypothesis:

Hypothesis I: if this represents a Mendelian ratio, the less frequent phenotype (black) must be homozygous recessive. Use a Punnett square to test this hypothesis (in this case, working backwards from the shaded section to the gametes).

This parent must be heterozygous, and therefore yellow



This parent must be heterozygous, and therefore yellow



Yellow homozygous


Yellow heterozygous



Yellow heterozygous

yy (Black = homozygous recessive

Hypothesis I is not supported, because both parents would need to be yellow for the arrangement to work. This is a null hypothesis.

Hypothesis II: if the black mice are recessive, the outcome of this mating does not represent a Mendelian ratio. Use a Punnett square to test this hypothesis (working backwards to the gametes).

This parent must be heterozygous, and therefore YELLOW



This parent must be homozygous, and therefore BLACK


Yy Yellow

yy Black


Yy Yellow

yy Black

This is an example of a backcross (see Question 9(b)(iii) above).

Simple answer: if a backcross normally results in a 50:50 split, why not this time? By chance, the ratio was skewed.

Extension: students may be interested that the probability of this actual result is easily calculated using a χ2 (chi-squared) test. Without going into the statistical explanation, the formula is based on the sum of the difference of each outcome (yellow + black) from the predicted result (which would be 10.5 of each phenotype, that is, 21÷2), squared to remove negative values, and divided by the predicted number:

χ2 = (16 − 10.5)2 + (5 − 10.5)2

10.5 10.5

= (5.5)2 + (−5.5)2


= 30.25/10.5 + 30.25/10.5

= 60.5/10.5

= 5.76

This number (5.76) is then compared to a distribution table for one degree of freedom (the number of degrees of freedom is always one less than the number of possible outcomes - and there were two outcomes in this example - black or yellow - 2-1). The number is between 3.84 and 6.64 on the one-degree of freedom χ2 table below (source for this standard example is

According to this table, the probability for this outcome is between 1% and 5%, which means that, by chance, from outcome will occur between 1% and 5% of the time. You also notice this section of the table is considered 'significant'. This may be an indication you may want to search for an alternative hypothesis, or alternatively breed more rats!

Degrees of freedom (df)

χ2 value [12]













P value (Probability)














Student responses will vary.

Student responses will vary.

Student responses will vary.

Student responses will vary.