Question

6. In guinea pigs, coat color can be white, cream or yellow. Of these three phenotypes, only the cream-colored guinea pigs never breed true. When two cream-colored guinea pigs are crossed, We are yellow, Y are cream and are white. A cream-colored guinea pig by white guinea cross yields / cream and white offspring. a. How many genes control coat color in the guinea pig? b. Give the mode of inheritance of coat color in the guinea pig. c. Why is it impossible for cream-colored guinea pigs to breed true?

Answer 1

a. As the cream colored character never be true,so it will be in a heterozygous condition.So will a homozygous dominant and homozygous recessive Condition also. So with all total there is 3 different possibilities of the coat color character.And this is only possible if there is only 1 gene control the character which have two allelic Condition, one is dominant which promote pigmentation and other is recessive which inhibit pigment formation. And these 2 alleles work in same manner as incomplete dominance works.

b. The crosses are shown in the picture will give a idea about inheritance pattern.
Let consider, Y is the donnant allele course yellow pigmentation y is the recessive allele innbit pigmentation, Parents YY Homozygous dernierant (Yellow) (Homozygens recessive) white gametes Yy (Heterozygous) (Cream Color) Here Y is not completely dominant over the y, That is why it is showing a intermediate character. This type of inheritance called as incomplete dominuance.

crossing of a cream Coloned guinea pig Parents. y X Yy. gametess Ý y yo Progeny - Yn YY Yellow White cream 1 : 2 ya ut

A cream colored pig crossed to with white colered Pig parents Yy x my (Cream) (white) for Gametes Yg - Cream yg - white,
c. This is an example of incomplete dominance type of inheritance where the intermediate character arise a the dominant allele cannot masks The expression of ressive allele completely in the heterozygous condition.Here the yellow and white color expressed at the homozygous dominant and recessive Condition.And at the intermediate heterozygous condition cream colored coat character is seen. That's why there is no chance of cream colored homozygous or true breed condition.