Principles Of Inheritance And Variation

Myopia is an example of complete sex linkage.

Intergenic interaction is shown by polygenes. This type of interaction occurs when two or more alleles of different genes present on same or different chromosomes interact to produce a cumulative effect. Multiple alleles, co-dominance and incomplete dominance are the examples of intragenic interactions.

Human blood groups are determined by the ABO gene, which has three alleles: , , and . The and alleles are codominant, while is recessive. The genotypes for the blood groups are: - Blood group AB: - Blood group O: The man with blood group AB has the genotype , and the woman with blood group O has the genotype . To find the probability of their child having blood group A, we use a Punnett square to determine the possible genotypes of their offspring. The man ( ) can contribute either an or an allele. The woman ( ) can only contribute an allele. The possible genotypes of the offspring are: - : Blood group A (since is dominant over ). - : Blood group B (since is dominant over ). The possible blood groups of the offspring are: - Blood group A ( ): 1 out of 2 possibilities. - Blood group B ( ): 1 out of 2 possibilities. Thus, the probability that their child will have blood group A is:

Color blindness is a sex-linked recessive trait caused by a recessive allele ( ) on the X chromosome. Normal vision is due to the dominant allele ( ). Since males have one X and one Y chromosome, their phenotype depends on the single X chromosome they carry. - The woman is color-blind, so her genotype is (homozygous recessive, as she expresses the recessive trait). - The man has normal vision, so his genotype is (hemizygous for the dominant allele). To determine the probability of their son being color-blind, we analyze the possible genotypes of their offspring using a Punnett square. The woman ( ) can only contribute an gamete. The man ( ) can contribute either an or a gamete. The possible offspring genotypes are: - Daughters ( ): They inherit one from the father and one from the mother. They are carriers (normal vision, as the dominant allele masks the recessive ). - Sons ( ): They inherit the from the mother and the from the father. Since the carries the recessive allele and there is no second X chromosome to mask it, they are color-blind. Since all sons will have the genotype , they will all be color-blind. Thus, the probability that their son will be color-blind is .

In Drosophila, the gene responsible for wing shape is the "vg" gene. The "vg+" allele represents the normal wing shape, while the "vg" allele is associated with vestigial (abnormal) wings. Therefore, the genotype for normal wings in Drosophila is "vg+", where the "+" indicates the dominant normal wing allele. - "vg" refers to the recessive allele for vestigial wings. - "vg no" and "vg ni" are not commonly associated genotypes in this context. Thus, the correct answer is option (A), "vg+".