Question 3

I threw in a different twist for this one.  The worksheet is available online.  You can use the same strategies as for the other two questions I modeled, but you need to create some information to help you identify the double crossover classes!

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F₁ beetle females of wild-type appearance but heterozygous for three autosomal genes are mated with males showing three autosomal recessive traits:  oval eyes, sleek bodies, and rippled thoraxes.  The progeny of this cross are distributed in the following phenotypic classes:

Phenotype	Number
Oval eyes, sleek body	29
Oval eyes, rippled thorax	559
Wild type	42
Rippled thorax	15
Sleek body	542
Oval eyes, sleek body, rippled thorax	35

1. Define appropriate gene and allele symbols according to standard conventions.
2.  Show the arrangement of alleles on the two homologous chromosomes in the parent (F₁) females.
3. Draw a genetic map based on these data. 
4.  Can you account for double crossovers?  Explain.

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The video solution is below:

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