Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
In one snail species, shell colour is determined by a gene with three alleles: allele $C^B$ gives a brown shell; allele $C^P$ gives a pink shell; allele $C^Y$ gives a yellow shell. Allele $C^B$ is dominant over both $C^P$ and $C^Y$, whereas $C^P$ is dominant over $C^Y$. Snail shells may also be banded, meaning they have dark stripes, or non-banded. The allele for non-banded, $N$, is dominant over the allele for banded, $n$.
(a)[2]
State the meanings of dominant and allele.
(b(i))[2]
A brown, non-banded snail is crossed with a pink, non-banded snail, and some of the offspring are both yellow and banded. State the genotypes of the two parents.
(b(ii))[2]
List the gametes produced by the parents.
(b(iii))[1]
State the genotype of offspring that are both yellow and banded.
(b(iv))[1]
Suggest the expected proportion of offspring that are both yellow and banded.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “A dominant allele is expressed in both homozygotes and heterozygotes.” …