Genetics
ABO blood groups in human are an example of discontinuous variation, whereas height is an example of continuous variation. Describe how these two examples differ in terms of:
Genetic control (i.e. the number of genes involved).
The effect of the environment on each characteristic.
The range of phenotypes.
Give one other example of continuous variation and one other example of discontinuous variation.
Continuous
Discontinuous
If height were entirely genetically controlled, what concordance would you expect between monozygotic twin pairs? Explain your answer.
Does data for eight-year-old twins suggest that height is largely controlled by genetic factors? Explain you answer.
Suggest an explanation for the low concordance at birth for monozygotic twins.
Explain the meaning of each of the following terms:
(i) Variation
(ii) Mutation
Explain how mutation causes variation. Give examples.
Explain how meiosis causes genetic variation in the gametes.
Complete the following table to show the different phenotypes you would expect in the F2 and their ratio.
Phenotype Ratio
State the ratio of phenotypes expected in the F2 offspring.
Mendel’s Second Law of inheritance states that, “during gamete formation the segregation of each gene pair is independent of other pairs.” How do the diagrams above prove this law? (AC 2.4).
Haemophiliacs possess a non-functional form of the gene responsible for the production of blood clotting factors. Shown below is the occurrence of haemophilia in one family.
Using the following symbols:
H = dominant allele h = recessive allele
State the genotypes of the following individuals.
Individual Genotype
1
2
3
5
6
9
2) On the basis of the information provided, is the inheritance of haemophilia:
(i) autosomal or sex-linked?
(ii) dominant or recessive?
State the probability of individual 8 being a carrier of haemophilia.
Explain why only females can be carriers of haemophilia.
Complete the following genetic diagram to show how parents who did not suffer from haemophilia, could have a son with haemophilia but also other children who did not suffer from haemophilia.
Phenotype of parents Genotype of parents Genotype of gametes
Normal male
Normal female
Genotype of offspring
Phenotype of offspring
What is the probability of the couple having a daughter with haemophilia?
What is the probability of the couple having another son with haemophilia?
Who’s gonna take you home tonight?
There has been a mix up in the maternity ward. The babies have managed to remove their wrist bands. On their wrist bands are their blood groups and names.
Billy Smith Blood group:A
Sarah Chadwick Blood group:AB
Imran Ahmed Blood group:B
Johnny Honest Blood group:O
Complete the table to match each parent to their baby by indicating the parental genotypes using the symbols IA, IB, and i, and then the name of the baby that belongs to each set of parents. Consider one blood type might have more than one genotype.
Parental Blood groups Parents Genotype Baby Blood Group
O and O
AB and O
A and O
AB and A
What is meant by epistasis?
The natural colouration of wild mice is called agouti and is produced from banded hairs. Two genes are involved, each with a dominant (A and B) and a recessive allele (a and b). The allele A codes for the ability to produce hair pigment: AA and Aa mice have pigmented hairs but all aa individuals are albinos. The B allele codes for the ability to make hair with grduated colouration: BB and Bb mice have graduated hair, bb mice have hair that is all one colour which is black.
Two agouti mice, genotypes AaBb, are bred together. What phenotypic ratio would you expect in the next generation? Set out the crosses using a Punnett square.
Gametes
Ratio:……………………………………
