Investigating Mendals rules of inheritance

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Heredity, genetics and protein synthesis

Genes are short sections of DNA strands. DNA makes identical copies of itself which is known as mitosis and carries information along the strands by way of coding (DNA’s code for making protein).

Genes are what make a person who they are. They influence the look on the outside and how we work on the inside. Genes, code protein for specific roles in the body for example insulin control, which is important in helping the body control the amount of sugar within the blood. A gene is the basic unit of genetics, and humans have around 20,000 to 25,000 genes.

Chromosomes are made of DNA (thus also genes). A chromosome contains thousands of genes and is all of these DNA molecules linked together in strands, packed tightly around proteins called histones, which make the structure of the chromosomes. Cell nucleus contains chromosomes made from long strands of DNA molecules. Chromosomes produce cells that are genetically identical to each other by way of mitosis.

Humans have 23 pairs of chromosomes in every cell, 46 chromosomes in total. The sex chromosomes determine if you are male (XY) or female (XX). DNA containing genes is stored in the cell’s nucleus.

Gregor Mendel was the man who discovered the fundamental principles of genetics through experiments that he carried out in his garden. His observations became the foundations of modern genetics and the study of heredity, and to date he is considered a pioneer in the field. At the time of Mendel’s research, people believed that offspring just inherited the genetics from their parents.

Mendal choose to use peas for his experiment because there are many distinct varieties. He cross fertilized the peas that had opposite characteristics and after analysing the results, he reached two of his most important conclusions. Law of segregation which showed that there are dominate and recessive characteristics passed down from parents to their offspring The Law of independent assortment which showed that certain traits were passed on from parents to their children.

Mendalls rules of inheritance found that paired pea traits were either dominated or recessive. When pure bred parent plants were cross bred, dominate traits were always seen and recessive traits were hidden until the first generation. From this he concluded that traits were not blended but remained distinct in generations down the line. This was what was believed at the time.

Genes are seen as a pair. Every characteristic comes in pairs. However some genes are more dominate than others. For example Brown eyes are more dominate than blue eyes. Blue eyes therefore being the recessive gene. This is displayed in the following example:

Homozygous means two genes that have exactly the same characteristics, and Heterozygous means two genes that are different.

R = ability to roll the tongue

r= cannot role the tongue.

Parents:

  • Female= rr
  • Male= Rr

""""From these parents the gametes would be:

r r R r

""""The offspring would be:

r rR r

The Punnett diagram shows that from a parents with a homozygous non-tongue roller (recessive) gene and the other parent having a Heterozygous roller gene that their children would have the tongue rollers gene around 75% of them, and the other 25% would be non-tongue rollers as they would not have inherited this characteristic from the genes of their parents.

r r

R r

r r

r r r r

R r r r

R r

R r r r

R R r r

The chemical Phenylthiocarbamide (PTC) is a chemical that some people can taste and others cannot dependant on if they have inherited this dominate gene.

T = ability to taste

t = none tasting

  • The T is dominate to the t
  • Both parents have the Tt gene.

""""Gametes

Tt

T

t

T

TT

Tt

t

Tt

tt

*tt is a non- taster gene.

The ratio of this Punnett diagram is 3:1, tasters to none tasters. 25% of the children would be none tasters as they would not have inherited this gene, whereas the other 75 % of the children would have inherited this dominate gene from the parents and will have the tasting gene (PTC).

Both male and female have two characteristics both with a dominate gene. Woman is a homozygous tongue roller and a non PTC taster, and the male is a heterozygous tongue roller and PTC taster.

Female= RRtt

Male= RrTt

Gametes

Female= RRtt

""Her offspring would be

Rt

Male= RrTt

His offspring could be

""""""""

RTRtrTrt

RT

Rt

rT

rt

RT

RRTt

RRtt

RrTt

Rrtt

Each of the above columns represents four children. Total 16 children.

  • 8 of the 16 children will have the taster and tongue roller gene.
  • 8 of the 16 children will only have the tongue roller gene.

Both male and female are heterozygous from both the above traits.

Male = RrTt

Female = RrTt

Gametes from the male would be

""""""""

RTrtRtrT

""""""""From the female would be:

RTrtrTRt

RT

rt

rT

Rt

RT

RRTT

RrTt

RrTT

RRTt

Rt

RrTt

rrtt

rrTt

Rrtt

Rt

RrTT

rrTt

rrTT

RrTt

Rt

RRTt

Rrtt

RrTt

RRtt

The ratio from this Pennett diagram is 9:3:3:1

  • 9 out of the 16 children will be both tongue rollers and have the PTC gene.
  • 3 out of the 16 children will be taster gene holders only and not have the tongue roller gene.
  • 3 out of the 16 children will have the tongue roller gene only and not the taster gene.
  • Only 1 child out of the 16 will have neither of these genes and will not be able to roll the tongue or taste the PTC chemical.

Genetic linkage means that genes are linked. Genes that are linked are genes that are found on the same chromosome. Genes whose loci are nearer to each other are less likely to be separated onto different chromatids during chromosomal crossover, so therefore they are said to be genetically linked. These genes can be passed down to offspring, e.g. if the parents have brown eyes then their child is going to have brown eyes, brown eye colouring is more dominate than blue.

During genetic linkage and the passing down to offspring of genes, cannot always be a positive thing, for example if the father is haemophilia then this gene is very likely to be passed on to the child. The way in which the genes from both sets of parents link together when producing offspring is what gives the offspring their characteristics.

The sex or gender is determined by the sex cells. The pairs of sex chromosomes (XX and XY) are separated. Females carry the XX sex chromosome, and males carry the XY chromosome. All normal female egg cell production by a human ovary has X chromosome. Half of the male sperm carry an X and half carry a Y.

The gender of a human baby is therefore determined by the sperm at the time it fertilises the female egg cell. If the sperm that fertilises carries an X chromosome then the baby will be a girl, however if the sperm that fertilises carries a Y chromosome, then it will be a boy.

Chromosomal cross over is the exchange of genetic material between homologous chromosomes (a set of one maternal chromosomes and one paternal chromosome that pair up with one another inside the cell during meiosis). This then results in recombination chromosomes. This is one of the final stages of the genetic recombination. The crossover of the chromosomes normally happens when matching regions on the matching chromosomes break and then they reconnect to the other chromosomes. The paired up chromosomes exchange different segments of their genetic material to form the recombination chromosome. This can also occur during the mitotic division, which can result in the loss of heterozygosis. The crossing over can also account for genetic variation, due to the swapping of the genetic material during cross veer, the centromere are no longer identical. So when meiosis II takes place and the chromosomes separate, some of the daughter cells receive daughter chromosomes with recombined alleles. Therefore due to this happening the offspring will have a different set of alleles and genes to what the parents have.

Continuous variation has no limits to the value of variants that can occur within a population. Line graphs are used to display this information.

Discontinuous variation is where people fall into a distinct category and based on features that cannot be measured across a complete range. You either have that characteristic or you don’t (such as hair colour, eye colour, able to role your tongue or not etc.). Chi-squared calculations work well to display this information.

Continuous variation

Discontinuous Variation

Height/ weight

Height/ weight can vary from person to person and a range of measurements are possible. Weight also fluctuates

Heart rate

Heart rate varies on many factors. The activity currently being undertaken, health levels, lifestyle etc.

Blood group

There are only four blood groups in which all humans fall into one of them and this cannot be changed

Finger print

Fingers prints are unique to an individual and no two are the same

Tongue rolling

Humans either fall into the category of either being able to tongue roll or not

Mutation happens when a DNA cell changes or is damaged in such a way that it alters the genetic messages carried by the gene. It is a permanent change in the DNA sequence that makes up a gene. Mutation can range in size from a single DNA base to a large segment of a chromosome. Gene mutation is most commonly caused by two types of occurrences. One being the environmental factors such as chemicals, radiation, and ultraviolet light from the sun can also cause mutations. The other form of mutation is caused by an error occurring during the reproduction of identical cells (mitosis). During the process of gametes. Chromosome mutation can result in changes in the number of chromosomes in a cell or changes to the structure of the chromosome. A chromosome mutation changes and impacts the entire chromosome.

De novo-mutation is a new mutation that occurs when an error in the copying of genetic material or cell division has happened. De novo mutation then results in the disease in the offspring.

De novo mutation occurs only in egg or sperm cells, or any cells that occur just after fertilization. De novo mutation may explain genetic disorders in which an effect child has a mutation in every cell, but has no family history of the disorder, becoming the first family member to have the disorder, and this is as a result of a mutation in the egg or sperm. A new mutation occurs in a somatic cell that can result in cancer.

Mosaicism is a condition where cell within a person have different genetic make-up. The condition can affect any type of cell, including the blood cells, egg and sperm cells (gametes) and the skin cells. Mosaicism is caused by an error in the division of the cells, very early in the development of the unborn baby. This error in cell division can cause the baby to be born with lifelong diseases such as mosaic Down syndrome, mosaic turner syndrome etc.

Polymorphism is a DNA sequence variation that is common in the population. It is a different version of the one gene. There are many forms of these genes. A discontinuous genetic variation divides the individuals in the population into two or more sharply distinct forms. Some examples of polymorphism are the separation of higher organisms into male and female sexes. Also the different blood types inn humans. Humans are all the same, but have unique factors about them we all have a blood group and these are not the same in everyone. If the frequency of two or more discontinuous forms within a certain species is too great to be explained by mutation, then the variation and the population displaying this, is then said to be polymorphic.

Protein synthesis happens when individual cells construct proteins and Both DNA (Deoxyribonucleic acid) and RNA (ribonucleic acid) are involved in the process. Enzymes within the cell nucleus begin synthesizing protein by unwinding the required sections of DNA so that RNA can be made. RNA then forms an identical copy of one side of DNA strand to be sent off to other areas of the cell. Binding of amino acids then take place.

Binding occurs through mechanical and chemical processes within cells when the strand of the RNA has been made in the nucleus. RNA is then a messenger (mRNA) and exits the nucleus through openings called nucleus pores and makes it way to the cytoplasm and towards the ribosome which act as the cells work station for protein synthesis.

mRNA then binds itself to the ribosome which triggers another piece of RNA to approach (tRNA). tRNA looks for the best place to bind to the mRNA and once it has, it attaches itself. Whilst holding an amino acid end, the ribosome then surrounds the strands of RNA and another tRNA approaches but this time carrying a different amino acid and the process happens again.

The two amino acids bind together with the help of the ribosome and energy from adenosine triphosphate (ATP) and the sequence repeats until the chain of amino acids grow. Once these amino acids have been replaced in the correct sequence, the chain then folds itself into a 3D shape, this then completes the protein.

Once completed the ribosome separates to be joined again later. This process takes place in numerous ribosomes and a healthy cell can produce hundreds of proteins every second.

Bibliography:

GCSE Bitesize (2014) Cell division [Online] Available from: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/celldivision/celldivision1. [Accessed: 4th September 2014]

BIO (2014) Monk Gregory Mendel [Online] Available from http://www.biography.com/people/gregor-mendel-39282#related-video-galler [Accessed: 4th September 2014]

Wikipedia (2014) Genetic Linkage [Online] Available from http://en.wikipedia.org/wiki/Genetic_linkage: [Accessed: 4th September 2014]

GCSE Bitesize (2014) Genes and Inheritance [Online] Available from http://www.bbc.co.uk/schools/gcsebitesize/science/21c_pre_2011/genetics/genesinheritencerev3.shtmlom: . [Accessed: 4th September 2014]

Wikipedia (2014) Chromosomal Cross over [Online] Available from http://en.wikipedia.org/wiki/Chromosomal_crossover [Accessed: 4th September 2014]

GCSE Bitesize (2014) Continuous and Discontinuous [Online] Available from http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/variation_classification/revision/3/ . [Accessed: 4th September 2014]

Genetics Home Reference (2014) what is a Gene Mutation [Online] Available from http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/genemutation . [Accessed: 4th September 2014]

Genetics Home Reference (2014) De Nova Mutation [Online] Available from http://ghr.nlm.nih.gov/glossary=denovomutation . [Accessed: 4th September 2014]

What is.com (2014)Polymorphism [Online] Available from http://whatis.techtarget.com/definition/polymorphism [Accessed: 4thSeptember 2014]

GCSE Bitesize (2014) RNA and Protein Synthesis [Online] Available from / http://www.bbc.co.uk/bitesize/higher/biology/cell_biology/rna/revision/2/ . [Accessed: 4th September 2014]

Reference list:

GCSE Bitesize (2014) Continuous and Discontinuous [Online] Available from http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/variation_classification/revision/3/ . [Accessed: 4th September 2014]#

Wikipedia (2014) Chromosomal Cross over [Online] Available from http://en.wikipedia.org/wiki/Chromosomal_crossover [Accessed: 4th September 2014]

BIO (2014) Monk Gregory Mendel [Online] Available from http://www.biography.com/people/gregor-mendel-39282#related-video-galler [Accessed: 4th September 2014]

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