Mendel’s rule of inheritance

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TAQ 1

What are genes and chromosomes and what do they do?

A gene is a short section of DNA. Each gene codes for a specific protein by specifying the order in which amino acids must be joined together (BBC Bitesize, 2014). A gene is the molecular unit of heredity of a living organism. It is used extensively by the scientific community as a name given to some stretches of deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) that code for a polypeptide or for an RNA chain that has a function in the organism. Genes are structures that are carried on larger structures called Chromosomes. These are thread-like structures and they usually occur in pairs that look exactly alike, these pairs are called homologous pair. Living beings depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's cells and pass genetic traits to offspring. All organisms have genes corresponding to various biological traits, some of which are instantly visible, such as eye color or number of limbs, and some of which are not, such as blood type, increased risk for specific diseases, or the thousands of basic biochemical processes that comprise life (Wikipedia, 2014).

Word Count: 194 words

TAQ 2

Discuss the work of the Austrian Monk Gregor Mendel. Work should include the following:

  1. Discuss the work of the Austrian Monk Gregor Mendel. Work should include Mendel’s rule of inheritance.

Gregor Mendel was an Austrian Monk. He was a scientist and found interest in heredity and went on to discover the modern rule of genetics. Mendel's pea plant experiments between 1856 and 1863 are now seen as ‘the rules of heredity’; however they are now known as ‘the laws of Mendelian inheritance’. Mendel experimented with seven characteristics of pea plants: plant height, pod shape and pod colour, seed shape and seed colour, flower position and colour. He used pea plant’s as the height, colours and shapes and a variety of plants could be kept close together and very accessible to evaluate at any time. His experiments showed many things. He showed that when a yellow pea and a green pea had offspring, the plant was always yellow. However, in the next generation of these plants, the green peas re-appeared at a ratio of 1:3. As this could seem complicated, Mendel created the terms “recessive” and “dominant” to describe these certain traits. In the example, green peas are recessive and yellow peas are dominant. His work shows and explains invisible factors (now called genes) in the passing from adult to child traits. Mendel also explained that allele (gene) pairs separate or segregate randomly from each other during the process of fertilization. Because allele pairs separate during gamete production, a male or female cell carries only one allele for each inherited trait. When these cells unite at fertilization, each contributes its own allele, ensuring the paired condition in the offspring. This is known as the Law of Segregation. Mendel also found that each pair of alleles moves independently off the other pairs during gamete formation. This is known as the Law of Independent Assortment. An individual is made up of the alleles it possesses. A person’s physical appearance is determined by the alleles it was made up by and by its environment. The presence of an allele does not necessarily mean that the trait will definitely be expressed. If the two alleles of an inherited pair differ; known as the heterozygous condition, then the dominant allele determines the organism’s appearance and the other has no noticeable effect on the appearance and is called the recessive allele. This is known as the Law of Dominance (Wikipedia, 2014).

Word Count: 373 words

  1. In Humans, there is a gene that controls the function of muscles of the tongue, allowing people with those muscles to roll their tongue and to those without to be unable to do so. Using a Punnet Diagram as part of your answer, discuss the children of a homozygous non tongue roller (recessive) and a heterozygous roller, and what proportion of children they would have.

Mother

t

t

Father

T

Tt

Tt

t

tt

tt

(T = ability to tongue roll)

(t = no ability to tongue roll)

The ability to tongue roll is 50%, therefore the couple would probably have the same children with the ability to tongue roll than without. Two shows the child being heterozygous tongue roller, the children would definitely be a tongue roller. Two shows heterozygous, in which case the child would take the dominant trait (ability to tongue roll) and would therefore be capable to do so.

Word Count: 80 words

  1. There is a chemical called Phenylthiocarbamate (PTC) which some people can taste and others can’t due to their genetics. The ability to taste the chemical is a dominant trait. Using a punnet diagram, discuss how two heterozygous parents would have children that can taste and those that cannot, and the proportions.

Mother

T

t

Father

T

TT

Tt

t

Tt

tt

(T = ability to taste)

(t = no ability to taste)

75% of the children of this couple would have the ability to taste PTC. One shows the child would be homozygous taster, so would definitely taste PTC. Another shows homozygous non-taster, so would not taste. The other two show heterozygous genes and therefore the dominant trait of being able to taste would therefore take lead and this proportion of children would be able to taste.

Word Count: 100 words

  1. Suppose a woman is both a homozygous tongue-roller and a non-PTC-taster marries a man who is a heterozygous tongue-roller and a heterozygous PTC taster. If these parents have plenty of children so that they had 16 in all, how many of those would you expect in each class?

Tongue roll

Mother

T

T

Father

T

TT

TT

t

Tt

Tt

PTC taster

Mother

t

t

Father

T

Tt

Tt

t

tt

tt

  1. Suppose one of the children who are heterozygous for both of the above traits and marries someone who is also heterozygous for both traits. Draw and explain a Punnet diagram for the offspring they may have.

Mother

T

t

Father

T

TT

Tt

T

Tt

tt

The children of these parents would have 75% chance of both tongue rolling and 75% chance of being able to taste PTC.

Word Count: 50 words

TAQ 3

  1. Explain genetic linkage and why it is important in the transmission of genetic characteristics.

Genetic linkage enables a recombination of genetics. Genetic linkage is the tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis (the process of genes being passed from parent to child). Genes that are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be genetically linked (Wikipedia, 2014). It allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction when gametes are formed. In this way new combinations of genes can occur in the offspring of a mating pair. Genes on the same chromosome would theoretically never recombine. During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. This process of chromosomal crossover generally occurs during meiosis, a series of cell divisions that creates haploid cells.

The probability of chromosomal crossover occurring between two given points on the chromosome is related to the distance between the points. For a long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. For genes that are closer together, however, the lower probability of crossover means that the genes demonstrate genetic linkage; alleles for the two genes tend to be inherited together. The amounts of linkage between a series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome (Wikipedia, 2014).

Word Count: 245 words

  1. Explain how sex or gender is determined.

The process that determines gender begins even before the male and female gametes join. Gametes are sex cells that contain exactly half of a complete genetic set, one half of each parent and one specific part of which determines sex. Eggs, the female gamete, contain only "X" chromosomes, but sperm, the male counterpart; can either have "X" or "Y" chromosomes. Whether the successful sperm was carrying an X or Y chromosome will be crucial in forming the gender of the offspring. For the first 10 weeks of human development, the embryo's sex is undifferentiated, meaning there are no particular characteristics of either sex. Or rather, both genders are present, and the baby could still go either way. Without the Y chromosome, the natural course of embryo development is for the gonads to become ovaries. Mullerian ducts develop into female genitalia as the proto-male genital structures weaken. But, if a Y chromosome is present and other conditions are normal, the production of testosterone by the embryo will trigger the formation of what are called Wolffian ducts, which will go on to form male genitalia. The Y chromosome causes the undifferentiated gonad to become a teste; what would have been the clitoris becomes the penis, the labia becomes a scrotum. By 12 weeks after fertilization, the chemical differentiation has occurred and external genital structures are observable after about 16 to 20 weeks (Ehow, 2014).

Word Count: 232 words

  1. Explain crossing over of chromosomes and the role it plays in transmission of genetic characteristics.

Genetic characteristics are made by a process whereby a special type of cell division occurs during formation of sperm and egg cells and gives the person the correct number of chromosomes. Since a sperm and egg unite during fertilization, each must have only half the number of chromosomes other body cells have. Otherwise, the fertilized cell would have too many. Inside the cells that produce sperm and eggs, chromosomes become paired. While they are pressed together, the chromosomes may break, and each may swap a portion of its genetic material for the matching portion from its mate. This process is called chromosome cross over. During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. During crossing over there are different characteristics which are passed from parent to child in terms of gender, eye colour, skin colour etc. If both parents have blue eyes it is likely their children will all have blue eyes as in their genes they carry this information to ensure blue eyes. When both their genes cross over from one another, they will come into contact with the other parents genes and as they both hold pure blue eyes. Even if they cross over and not one colour is dominant the child will end up with blue eyes.

Word Count: 216 words

TAQ 4

Using examples, explain the difference between continuous and discontinuous variations.

Within a classification system there are different species, such as humans, dogs, cats, lions and tigers. There can be major variation between different species, however for the same species, there are also variation and this is described into two categories; continuous and discontinuous variation. Continuous variation describes features such as height, weight and length of foot. This means that for example if a graph was drawn to show the shoe size of an adult female; the graph would start at size 2 and end at size 10; this means that most adult females in the world would fit in between these marks. However some may be smaller or larger than this, this shows continuous variation as it can always change. Discontinuous variation is when there is no change. Such as blood group, eye colour and gender. There are only 4 blood groups, so every human has one of those 4 blood types. And there are only a few colours that eyes can be. This shows discontinuous variation as there is no change.

Word Count: 172 words

TAQ 5

  1. Define the term mutation and how it is caused?

A gene mutation is a permanent damage/change in the DNA sequence that makes up a gene. Mutations range in size from a single DNA building block (DNA base) to a large segment of a chromosome. Gene mutations occur in two ways; they can be inherited from a parent or acquired during a person’s lifetime. Mutations that are passed from parent to child are called hereditary or germ line mutations. Acquired mutations occur in the DNA of individual cells at some point in a person’s life. These changes can be made by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. (DLC, 2014)

Word Count: 116 words

  1. Describe de nuvo mutations and provide one example.

The term de nuvo mutations describe alterations in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself (GHR, 2014). Proteus syndrome is characterized by progressive, segmental or patchy overgrowth of diverse tissues of all germ layers, most commonly affecting the skeleton, skin, and adipose and central nervous systems (NCBI, 2014). This means it can cause skin overgrowth and atypical bone development, it does not run in families.

Word Count: 95 words

  1. Describe mosaicism and provide one example.

Mosaicism is a condition in which cells within the same person have a different genetic makeup and they are very uncommon, usually effecting less than 1% of the population. Mosaicism can affect any type of cell, including: Blood cells, Egg and sperm cells, Skin cells (MLO, 2014). Mosaicism means the presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg. The phenomenon was discovered by Curt Stern. He demonstrated that genetic recombination, normal in meiosis, can also take place in mitosis. When it does, it results in somatic mosaics. These are organisms which contain two or more genetically distinct types of tissue (Wikipedia, 2014). An example of this is mosaic Down Syndrome. The symptoms can vary and may not be as severe if the person has both normal and abnormal cells.

Word Count: 143 words

  1. Describe polymorphism and provide one example.

Polymorphism is a term used to describe common changes to genes. They are common enough to be considered a normal variation in DNA, a DNA sequence variation that is common in the population. In this case no single allele is regarded as the standard sequence. Polymorphisms are responsible for many of the ‘normal’ differences between people such as eye colour, hair colour, blood type. On contrast to mosaicism, polymorphisms do not directly affect a person’s health, but some of these variations may increase/decrease the risk of developing certain disorders. However, A rare disease allele in one population can become a polymorphism in another if it confers an advantage and increases in frequency. A good example is the allele of sickle-cell disease. In Caucasian populations this is a rare sequence variant of the beta-globin gene that causes a severely debilitating blood disorder. In certain parts of Africa, however, the same allele is polymorphic because it confers resistance to the blood-borne parasite that causes malaria (Wellcome Trust, 2014).

Word Count: 166 words

TAQ 6

  1. What does protein synthesis mean and where does it take place?

Protein synthesis is a two part process that involves DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic acid). It is responsible for the making and distributing of the millions of different proteins the body requires.

  1. What are the two main stages of protein synthesis?

Transcription and Translation.

During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript. As opposed to DNA replication, transcription results in an RNA complement that includes the nucleotide uracil in all instances where thymine would have occurred in a DNA complement (Wikipedia, 2014).

Translation is the process in which cellular ribosomes create proteins. It is part of the process of gene expression. In translation, messenger RNA (mRNA) produced by transcription is decoded by a ribosome complex to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein (lbid).

  1. Explain each of the two stages listed in part 2 above.

The first step of protein synthesis is called Transcription, this is when the 2 DNA strands in a gene that codes for a protein, unzip itself from the other. Then, a single strand of messenger RNA is then made by pairing up RNA bases with the exposed DNA nucleotide bases. After the RNA is manufactured the second process of Translation starts. The RNA leaves the cell nucleus and travels to a cellular organelle, the ribosome. In there the RNA code is translated into a transfer RNA code which is transferred into a protein sequence. In this process, each set of 3 RNA bases will pair with a complimentary RNA base triplet. Each RNA is specific to an amino acid, and together with peptide bonds, a protein is formed and released (DLC, 2014).

Word Count: 293 words

Bibliography

Classification Systems, 2014. BBC Bitesize [Online]. Available at: <http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/variation_classification/revision/3/> [Accessed on 11th May 2014]

Gene, 2014. Wikipedia [Online]. Available at: <http://en.wikipedia.org/wiki/Gene> [Accessed on 11th May 2014].

Genes, 2014. BBC Bitesize [Online]. Available at: <http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/genes/> [Accessed on 11th May 2014].

Genetic Linkage, 2014. Wikipedia [Online]. Available at: <http://en.wikipedia.org/wiki/Genetics#Recombination_and_genetic_linkage> [Accessed on 11th May 2014].

Genetic Recombination, 2014. Access Excellence [Online]. Available at: <http://www.accessexcellence.org/RC/AB/BC/Genetic_Recombination.php> [Accessed on 11th May 2014].

Gregor Mendel, 2014. Wikipedia [Online]. Available at: < http://en.wikipedia.org/wiki/Gregor_mendel> [Accessed on 11th May 2014].

How is Gender determined, 2014. Ehow [Online]. Available at: <http://www.ehow.com/how-does_4572288_how-gender-determined.html#ixzz317SfrUBc> [Accessed on 11th May 2014]

Mendelian Inheritance, 2014. Wikipedia [Online]. Available at: < http://en.wikipedia.org/wiki/Mendelian_inheritance> [Accessed on 11th May 2014].

Mosaicism, 2014. Medline Plus [Online]. Available at: <http://www.nlm.nih.gov/medlineplus/ency/article/001317.htm> [Accessed on 11th May 2014].

Mutation of Polymorphism, 2014. Wellcome [Online]. Available at: <http://genome.wellcome.ac.uk/doc_wtd020780.html>[Accessed on 11th May 2014]

Translation, 2014. Wikipedia [Online]. Available at: <http://en.wikipedia.org/wiki/Translation_(biology)> [Accessed on 11th May 2014].

Transcription, 2014. Wikipedia [Online]. Available at: <http://en.wikipedia.org/wiki/Transcription_(genetics) > [Accessed on 11th May 2014].

Unit 1, 2014. Human Biological Science 2, Distance Learning centre [Online]. Available at: <http://www.distancelearningcentre.com/units.php> [Accessed on 11th May 2014].

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