1. An organism's phenotype is their observable features. What does an organism's phenotype result from ?
Answer
Its genotype and the interaction of these genes with the environment.
2. A single gene may have many alleles. These alleles can be categorised into one of three "groups". What are these groups called and what does that mean about the allele ?
Answer
Dominant: only need one copy of the allele to be expressed in the phenotype.
Recessive: requires an organism to possess two of these alleles in order for it to be expressed in the phenotype.
Co-dominant: both alleles contribute to the phenotype.
3. A student carried out a genetic cross using fruit flies and obtained a large number of offspring. She counted the number of offspring with each phenotype. What statistical test should she use to find out whether the ratio of phenotypes obtained in the cross are consistent with the theoretical prediction ?
Answer
Chi squared test.
4. What is meant by the term "autosomal linkage" ?
Answer
An autosome is any chromosome that is not a sex chromosome. Linkage is when two genes are on the same chromosome. So autosomal linkage refers to two genes on the same autosome.
5. A snail's phenotype varies depending on where it is found. One gene with two alleles determines the presence of bands.
The allele B (unbanded) is dominant over the allele b (banded). Shell colour is determined by a single gene (C) with three different alleles.
In order of dominance, CB(brown) is dominant over CP(pink) which is dominant over CY (yellow). Give the possible genotype(s) of an unbanded yellow snail and a banded pink snail.
Answer
unbanded yellow: BbCYCY and BBCYCY
banded pink: bbCPCP and bbCPCY
6. A brown unbanded snail was crossed with a pink banded snail. Among the offspring were both banded and unbanded snails of all three colours. Use a genetic diagram to show the genotypes of the parents, the gametes and the phenotypes of the offspring.
Answer
Parent genotypes: CBCYBb and CPCYbb
Gametes: CBB, CYB, CBb, CYb and CPb, CYb
Offspring phenotypes: 2 brown unbanded, 1 pink unbanded, 1 yellow unbanded, 2 brown banded, 1 pink banded and 1 yellow banded.
7. Scientists believe that darker snails can absorb heat more effciently and this enables them to survive where it is cooler. On the other hand, in warmer climates, yellow snails heat up less quickly. Use your knowledge of natural selection to explain why yellow snails are more common in warmer areas.
Answer
Yellow snails are more likely to survive in warmer areas. As a result, they reproduce more and pass on their alleles. This means the yellow allele increases in frequency.
8. Scientists noticed that banded snails are more common in woodland than grassland. They thought that this might be because of predation by birds that eat snails. Scientists thought that banded snails might be better camouflaged. In an investigation, scientists removed all the snails from an area of woodland. Then they released equal numbers of banded and unbanded snails. Over the next two weeks, the scientists counted how many banded and unbanded snails were eaten. The scientists carried out a statistical test on these data. What null hypothesis would they have used ?
Answer
There is no difference in the number of banded and unbanded snails eaten by birds. Banded and unbanded snails are equally likely to be eaten by birds.
9. There are two genes that contribute to the coat colour of Labrador dogs. One gene determines whether the pigment is present in the skin and fur or only present in the skin. The allele for pigmentation in the fur (E) is dominant. Without pigmentation in the fur (caused by the recessive allele e) the Labrador has a yellow coat. The other gene determines whether the pigment is black or brown. The allele for black colour (B) is dominant over brown (b). Name this type of interaction between two genes.
Answer
This type of interaction is called epistasis.
10. Give the phenotype of the genotypes eeBb and Eebb.
Answer
eeBb = yellow, Eebb = brown
11. A Labrador of genotype Eebb was crossed with a Labrador of genotype EeBb. Use a genetic diagram to show the ratio of possible genotypes and phenotypes in the offspring.
Answer
Ratio is 3 black : 3 brown : 2 yellow