Question 2

This question can confuse some students because it conforms to the convention of not saying what the wild-type features look like.  Only mutations are written in the description.  If a feature isn't noted, then you can assume it's wild-type.  Also be careful when determining the order of the genes and whether they're in coupling or not!  It's from a worksheet that is available online.

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A homozygous female with mutations for vestigial wings, blue body, and purple eye colour was mated to a wild-type male.  All the triple hets had blue bodies.  The F₁ females were testcrossed and eight classes of progeny were classified as follows:

 

Phenotype	Number
vestigial, blue, purple	1572
wild-type	1553
blue, purple	129
vestigial	118
blue	29
vestigial, purple	39
vestigial, blue	1
purple	4

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1. Define appropriate gene and allele symbols according to standard conventions.
2. Diagram the arrangement of alleles on the two homologous chromosomes for both parents (P generation) and the F₁.
3. Draw a genetic map based on these data.  Be sure to mathematically correct for double-crossovers.

Try this question before looking at the video solution below:

(you can get a full-screen version by clicking on the YouTube logo at the bottom-right hand side of the video above).