Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
In Drosophila melanogaster, the fruit fly, body colour and eye colour are determined by two separate genes. G/g are alleles of the body colour gene: G gives a grey body, whereas g gives a black body. R/r are alleles of the eye colour gene: R gives red eyes, whereas r gives brown eyes. Both genes are autosomal. A dihybrid cross was set up between a fly with grey body and red eyes and a fly with black body and brown eyes. Each parent was homozygous for both genes. The F1 offspring were then crossed to produce the F2 offspring.
(a)[2]
A statistical test indicated that the cross results were significantly different from those predicted. State the name of the statistical test used and state the expected phenotypic ratio for the F2 generation.
(b)[4]
A test cross may be used to identify F2 flies that are heterozygous for both genes. Draw a genetic diagram to show how a test cross between a heterozygous grey-bodied, red-eyed F2 fly and a fly with a black body and brown eyes can yield four distinct offspring phenotypes. Use the symbols G/g and R/r.
(c)[5]
The outcomes of the test cross in (b) are given in Table 2.1. These outcomes are significantly different from the expected outcomes. Describe how the results differ from what was expected and explain why they differ.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme.