a1. A single gene controls the presence of hair on the skin of cattle. The gene

ID: 162796 • Letter: A

Question

a1. A single gene controls the presence of hair on the skin of cattle. The gene is its on the x dominant allele causes hair to be present on the skin and recessive allele causes The diagram shows the pattern of inheritance of these alleles in a group of cattle. Hetrioas melo Hainees female Male hair Female har (a) Use evidence from the diagram to explain that hairlessness is caused by a recessive allele (ii) that hairlessness is caused by a gene on the X chromosome. (b) What is the probability of the next calf born to animals 5 and 6 being hairless? Complete the genetic diagram to show how you arrived at your answer. Female with hair Phenotypes of parents Male with hair

Explanation / Answer

ii) The trait shows sex bias. Here males are more affected. Thus the allele is present in X chromosome.

2. According to the rule of Sex linked recessive inheritance there must be 50 % probability that the next calf born to animals 5 and 6 will be hairless.

GENOTYPES AND PHENOTYPES

2) A) I) The allele whose phenotypic expression is not expressed in the heterozygous state is called recessive allele. For example, the genotype of F1 tall plant of Monohybrid cross is Tt. Here t is a recessive allele and T is a dominant allele.

ii) Alleles that lack dominant and recessive relationship and both bears the potentiality to express phenotypically in the heterozygous state is called codominant allele.

E.g. Human MN blood group antigens

GENOTYPES

PHENOTYPES

LMLM

M BLOOD GROUP

LMLN

MN BLOOD GROUP

LNLN

N BLOOD GROUP

B) i) There is no skip of generation of the trait i.e. trait is present in every generation .Hence the allele is dominant

ii) The trait does not show sex bias means males and females are equally affected. Thus it is not present on X chromosome. It is present on the autosome.