Biology 9700 · AS & A Level · Passage of information from parents to offspring

Passage of information from parents to offspring — practice question

Domestic rabbits show variation in both fur length and fur colour. Fig. 6.1 illustrates a domestic rabbit with short fur and the Himalayan fur-colour pattern. The two genes controlling the length and colour of this rabbit’s fur are located at the A / a locus and the B / b$^h$ / b locus. These two gene loci are found on different chromosomes. • The allele A gives short fur. • The allele a gives long fur. • A is dominant over a. • The allele B gives black fur over the whole body. • The allele b$^h$ gives black fur on the nose, ears, paws and tail of the rabbit, with white fur on the rest of the body (Himalayan pattern). • The allele b gives white fur over the whole body (albino). • B is dominant over b$^h$ and b$^h$ is dominant over b.
(a(i))[2]

State the four possible genotypes of the rabbit shown in Fig. 6.1.

(a(ii))[1]

A phenotype of rabbit breeds true. This means that when it is crossed with a rabbit that looks the same, every offspring resembles the parents. Describe the phenotype of the rabbit that breeds true.

(b)[5]

A rabbit with long, black fur over the whole body and homozygous at both loci was crossed with a rabbit with short, white fur and homozygous at both loci. The F1 offspring had short, black fur. These F1 rabbits were then crossed with each other to form the parents of the F2 generation. Draw a genetic diagram to predict the F2 offspring genotypes and the ratio of F2 offspring phenotypes. Include: • F1 genotypes • gametes • F2 offspring genotypes • ratio of F2 offspring phenotypes.

(c(i))[3]

Explain why the two genes show independent assortment.

(c(ii))[1]

The rabbit breeder entered the results into a table and began calculating the $\chi^2$ value. Table 6.1 shows the results together with some of the calculations already made. Calculate the expected numbers and place them in the shaded column in Table 6.1.

(c(iii))[1]

Use the formula given and the figures in Table 6.1 to calculate the $\chi^2$ value. $\chi^2 = \Sigma \frac{(O - E)^2}{E}$ Calculate $\chi^2$.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Possible genotypes: $AAbb^{hh}$, $Aabb^{hh}$, $AAbb^h$, $Aabb^h$” …

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