Question

In mice,yellow coat color (Z) is a dominant factor and black (z) is it's recessive. The homozygous condition (ZZ) is lethal and kills the embryo within a few days after conception. If two yellow mice bred, what genotypes would you expect and in what ratio? What will be the phenotypes and in what ration?

Answer 1

Genotypic ratio

Pattern of offspring distribution according to genotype (i.e. the genotype constitution determining the phenotype of an organism)

The genotypic ratio describes the number of times a genotype would apper in the offspring after a test cross. For this example, a test cross between two organisms with same genotype, Zz, for a heterozygous dominant trail will result in offspring with genotype, RR, Rr, and rr. in this example, the genotypic ratio is 1:2:1. But the homozygous condition (ZZ) is lethal and kills the embryo within a few days so the result of this genotype ratio is 2:1

Phenotypic ratio

(genetics) Pattern of offspring distribution according to phenotype (i.e. observable characteristic)

Phenotypic ratio pertains to the relative number of offspring manifesting a particular trail or combination of traits. It can be determined by doing a TEST CROSS and identifying the frequency of a trait or trait combinations that will be expressed based on the genotypes of the offspring.

test cross= the cross of an organism with an unknown dominant genotype with an organism that is homozygous recessive for that trait.

In this example to getermine the phynotypic ratio, the number of times the phynotypes are expressed is counted. In this case phynotypic ratio is 1:1(how many of the offspring will be based on the genotype).