What are the genotypes of the parents on each of the following crosses: appear m

Question

What are the genotypes of the parents on each of the following crosses:

appear m the 2idm what proportions GO In mice, the allele C for colored fur is dominant over the allele c for white fur, and the allele V for normal behavior is dominant over the allele v for waltzing behavior, a form of discoordination. Give the genotypes of the 3.6 parents in each of the following crosses: (a) Colored, normal mice mated with white, normal mice pro- duced 29 colored, normal and 10 colored, waltzing progeny. (b) Colored, normal mice mated with colored, normal mice produced 38 colored, normal, 15 colored, waltzing, 11 white, normal, and 4 white, waltzing progeny. (c) Colored, normal mice mated with white, waltzing mice produced 8 colored, normal, 7 colored, waltzing, 9 white, normal, and 6 white, waltzing progeny.

Explanation / Answer

a) in the first cross if you observed that progeny is produce in the ratio of 29: 10 means approx 30: 10 so 3:1. This phenotype ratio is appear only when one trait is heterozygous in both the parent. In the progeny phenotype no white fur means C gene is not heterozygous but waltzing behaviour in progeny indicates presence of heteozygous V gene in both the parents . So genotype of parents are

CCVv x ccVv

It gives CcVV, CcVv, CcVv, Ccvv progeny genotype

If V gene is homozygous fro one of the parent than there is no waltzing behaviour in progeny observed.

b) In this cross most probable genotype is

CcVv x CcVv

Both trait fur colour or behaviour are heterozygous because coloured normal mice producing all the four phenotype that is approximately in the ratio of 9:3:3:1.

If you take homozygous for any of trait in either of the parent you will not get progeny phenotype given in this question means both parents are heterozygous for both the trait.

c) Here, one parent genotype will be ccvv because it contain recessive phenotype that express only in homozygous condition.

Other parent is coloured normal means genotype either CcVv or CCVV or CCVv or CcVV

So, we check the progeny by crossing between different combination. Among all the genotype , CcVv genotype is of another parent which give approx 1:1:1:1 ratio.this is the test cross. If you use any other genotype you will not get the progeny phenotype given in section c. CcVv x ccvv

Give CcVv , Ccvv, ccVv, ccvv.

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