N cattle, an autosomal mutation called Dexter produces calves with short stature and short limbs. Embryos that are homozygous for the Dexter mutation have severely stunted development and either spontaneously abort or are stillborn. In addition roan cattle are the heterozygous hybrids of a cross between a white individual and a red individual. What progeny phenotypes do you expect from the cross of a roan Dexter cow to a roan Dexter bull

1 DDRR - Red, non-dexter

2 DDRr - Roan, non-dexter

2 DdRR - Red, dexter

4 DdRr - Roan, dexter

1 DDrr - white, non-dexter

2 Ddrr - white, dexter

Explanation:

Dexter is deleterious in homozygous condition, hence, phenotypes are heterozygous.

Roan are also heterozygous.

If dexter allele is represented by D, non dexter individuals will be DD dexter individuals will have the genotype Dd.

If colour in cattle is represented by R, red individuals will be RR, white will be rr, then roan colour will be Rr.

Hence, roan dexter cow and roan dexter bull will both have DdRr genotypes.

Crossing the two:    DdRr   x   DdRr

Progeny:

1 DDRR - Red, non-dexter

2 DDRr - Roan, non-dexter

2 DdRR - Red, dexter

4 DdRr - Roan, dexter

1 DDrr - white, non-dexter

2 Ddrr - white, dexter

Others that are either aborted or stillbirths include:

1 ddRR

2 ddRr

1 ddrr

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