TOPIC H: GENETIC BASIS FOR VARIATION

Question 1

What is gene linkage?

Answer 1

When two genes are located on the same chromosome, they are described as being linked.
All genes on a single chromosome form a linkage group. Linked genes are usually inherited together in genetic crosses because they are part of a single chromosome which is along as a single unit.
As a result linked genes do not exhibit independent assortment.

Question 2

What is recessive epistasis?

Answer 2

Gene A and B code for enzymes which are involved in a metabolic pathway in the synthesis of pigment. Enzyme A catalyses a reaction to form the product, which becomes the substrate of the next enzymes B to form another product.
In the presence of allele A, pigments can be synthesised.
Homozygous recessive alleles at gene locus A suppress the expression of gene B.

Question 3

What is complementary loci epistasis?

Answer 3

A—>B
At least one dominant allele from each gene locus is necessary for the synthesis of anthocyanin pigment to ensure both biochem conversions to the final purple product. As both genes are required for the purple flower phenotype, this epistatic interaction is called complementary loci.
Homozygous recessive condition at gene locus A or B suppresses the phenotypic effects of gene B. Homozygous recessive condition of either gene A or gene B is epistatic over the dominant allele of the other gene.

Question 4

What is dominant epistasis?

Answer 4

Gene a and B are involved in a metabolic pathway in the synthesis of pigment in ()
A dominant allele at gene locus A will mask any phenotypic effect of gene B.