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

Passage of information from parents to offspring — practice question

The fruit fly, Drosophila melanogaster, is used extensively in genetic research. It shows many phenotypic variants in traits such as body colour, wing shape and eye colour. Two alternatives to the normal-winged, grey-bodied phenotype are: • vestigial (very short) wings, controlled by the recessive allele of the gene N/n • ebony (black) body colour, controlled by the recessive allele of the gene G/g.
(a)[2]

Using the symbols provided, state the genotypes that a normal-winged, grey-bodied fruit fly could have.

(b)[3]

Describe how you could find the genotype of a normal-winged, grey-bodied fly.

(c)[4]

A gene that controls eye colour is found on the X chromosome. It has different alleles for red eyes, orange eyes and white eyes. The allele for red eyes ($R$) is dominant over the allele for orange eyes ($o$) and also over the allele for white eyes ($w$). The allele for orange eyes is dominant over the allele for white eyes. Using these symbols, draw a genetic diagram to show how a cross between a white-eyed male fruit fly and a red-eyed female fruit fly produces male and female offspring that are either red-eyed or orange-eyed.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The correct genotypes are NNGG, NNGg, NnGG and NnGg” …

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