In the yellow fever mosquito Aedes aegypti sex is determined

In the yellow fever mosquito, Aedes aegypti, sex is determined by a single pair of alleles, M and m, where the genotypes MM and Mm develop as males, and the homozygous mm genotype is female. The recessive gene bz for bronze body color (the dominant allele bz+ results in black body color) is linked to the sex-determining gene and recombines with it at a frequency of 8%.

a. In the cross of a heterozygous bz+ M/bz m male with a bronze female, what genotypes and phenotypes of progeny are expected? What are the expected genotypic and phenotypic frequencies?

b. In the cross of a heterozygous bz M/bz+ m male with a bronze female, what genotypes and phenotypes of progeny are expected? What are the expected genotypic and phenotypic frequencies?

c. What is the principle difference between the male genotypes in parts a) and b) of this question? Which genotype is the coupling (cis) genotype and which is the repulsion (trans) genotype?

Solution

In the yellow fever mosquito, Aedes aegypti, sex is determined by a single pair of alleles, M and m, where the genotypes MM and Mm develop as males, and the homozygous mm genotype is female. The recessive gene bz for bronze body color (the dominant allele bz+ results in black body color) is linked to the sex-determining gene and recombines with it at a frequency of 8%.

a. In the cross of a heterozygous bz+ M/bz m male with a bronze female, what genotypes and phenotypes of progeny are expected? What are the expected genotypic and phenotypic frequencies?

In the cross of a heterozygous bz+ M/bz m male with a bronze female, what genotypes and phenotypes of progeny are expected?

All the female gametes are bz m.

The male gametes are bz+M with frequency (1 - 0.08)/2 = 46 percent,

bz m with frequency 46percent,

bz+m with frequency 0.08/2 = 4 percent,

and bz M with frequency 4 percent.

The progeny are therefore black males (bz+ M/bz m) with frequency 46 percent,

bronze females (bz m/bz m) with frequency 46 percent,

black females (bz+ m/bz m) with frequency 4 percent,

and bronze males (bz M/bz m) with frequency 4 percent).

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b. In the cross of a heterozygous bz M/bz+ m male with a bronze female, what genotypes and phenotypes of progeny are expected? What are the expected genotypic and phenotypic frequencies?

heterozygous bz M/bz+ m male with bronze females (bz m/bz m)

bz m

bz+ M

bz m bz+ M

Black male

1/4

bz+ m

bz m bz+ m

black females

1/4

bz M

bz m bz M

Bronze male

1/4

bz m

bz m bz m

bronze females

1/4