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

Passage of information from parents to offspring — practice question

Fig. $5.1$ depicts a cat displaying the recessive phenotype for two unlinked genes. $H/h$ determines hair length. The allele for short hair is dominant to the allele for long hair. $R/r$ determines coat pattern. The allele for 'full colour', with pigment on all parts of the body, is dominant to the allele for 'pointed', where the pigment is confined to the ears, face, paws and tail.
(a)[5]

Draw a genetic diagram to predict the genotypes and phenotypes of the offspring when the cat in Fig. $5.1$ is crossed with a cat heterozygous for the hair length gene and heterozygous for the coat pattern gene. Include: parental phenotypes; parental genotypes; gametes; $F_1$ genotypes; $F_1$ phenotypes.

(b)[5]

Researchers isolated two DNA sections thought to match the allele for full colour ($R$) and the allele for pointed ($r$). When these two DNA sections were sequenced, the DNA sequence for full colour, $R$, was found to include a restriction site for the restriction enzyme $\textit{HpaII}$. That restriction site was absent from the DNA sequence $r$ because of a single nucleotide substitution.

(c(i))[1]

Identify evidence in Fig. 5.2 that the pointed phenotype is caused by a recessive allele.

(c(ii))[2]

Identify evidence in Fig. 5.2 that shows the $R/r$ gene lies on an autosome.

(c(iii))[2]

Identify evidence in Fig. 5.2 that the marker locus and $R/r$ are closely linked.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: Accurate parental phenotypes and genotypes

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