What are the genotypes of the parents in a standard dihyrbid test cross? For exa

Question

What are the genotypes of the parents in a standard dihyrbid test cross?

For example, if a standard test cross is conducted for the linked genes for curved (c, curved wings) and plexus (px, extra wing veins) wings in Drosophila produces a progeny with the following phenotypes:

c px / c px 80

c + / c px 400

+ +/ c px 90

+ px/ c px 430

I am aware that the genotypes with the highest frequency are paretnals ( so in this case the genotypes associated with 400 and 430) but why isn't one of the genotypes c px/c px? Afterall, doesn't a standard test cross require are homozygous recessive individual?

Thank you

Explanation / Answer

ANSWER:

A Genotype of the parents:

Two genotype with highest number of offspring are parental genotype c + / c px and + px/ c px .

The curved and plexus mutant alleles are in replusion linkage because of genotypes are with one wildtype allele and one mutant allele.coupling cross genotype will have either two wildtype or two mutant alleles.

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