Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
Raspberry plant stems carry spines. Fig. 7.1 illustrates part of a raspberry plant. Two genes, $A/a$ and $B/b$, determine the colour of the spines. These genes are located on separate pairs of chromosomes.
Allele $A$ causes a pink anthocyanin pigment to be produced in the spines.
Allele $B$ has no effect on its own, but it enhances the colour produced by allele $A$ so that the spines are red.
Alleles $a$ and $b$ do not affect colour.
If anthocyanin is absent, the spines are green.
(a)[2]
State the spine colour shown by raspberry plants with genotypes $Aabb$ and $aaBB$.
(b)[5]
Plants with genotype $AaBb$ were crossed with plants with genotype $aabb$. The seeds produced were sown, and the seedlings were grown until their stems developed spines. Use a genetic diagram to show the result of this cross, including the ratio of offspring phenotypes.
(c)[2]
Suggest why the ratio shown in your genetic diagram would differ if the genes $A/a$ and $B/b$ were located on the same homologous pair of chromosomes.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The genotype $Aabb$ gives a pink phenotype” …