Answer to Question #341868 in Genetics for Mutamba

Question

Discuss the role the following pieces of evidence played in the making of chromosomal

theory of heredity:

a) The discovery of the white fly.

b) The microscopic evidence for chromosome pair crossing over.

c) The coupling factors on the Drosophila X chromosome.

Answer 1

a) When Morgan bred mutant flies with white eyes, he noticed that in one generation only male flies had white eyes. After conducting control breeding, Morgan determined that the gene that determines eye color in flies is sex-linked;

b) When Janssens examined the chromosomes during meiosis under a microscope, he saw them in a tangled state. According to Janssens, Morgan determined that breaks are formed in the chromosomes and they thereby exchange their parts with each other. Thus, the exchange of genetic information is occurred;

c) Morgan found coupling factors at various locations in the Drosophila X chromosome. He thereby made an addition to Mendel's second law, explaining why, when two heterozygotes are crossed, the ratio of genotypes in the next generation does not always go out 1:2:1, and phenotypes — not always 3:1.