Chromosomal Inheritance in Fruit Flies

Chromosomal Inheritance and Thomas Morgan's Discoveries

• Thomas Morgan was the first to associate a specific gene with its corresponding chromosome.
• Utilized the fruit fly, Drosophila melanogaster, for genetic studies due to its rapid breeding cycle and manageable number of chromosomes.

Reasons for Using Fruit Flies

• Fruit flies breed quickly and produce a large quantity of offspring that can reproduce in approximately two weeks.
• They possess only four pairs of chromosomes, including three pairs of autosomes and one pair of sex chromosomes.

Initial Findings

• Wild-type fruit flies typically exhibit red eyes.
• After a year of breeding, Morgan identified a white-eyed male fruit fly, representing a mutant phenotype.
• Crossed a white-eyed male (mutant) with a red-eyed female (wild type).

Genetic Crosses

• Initial cross between white-eyed male (rr) and red-eyed female (RR) produced F1 generation, all of which had red eyes (Rr genotype).
• In a subsequent cross of the F1 generation (Rr x Rr), the offspring showed a Mendelian ratio:
  • 3:1 ratio of red-eyed to white-eyed flies.
  • All females were red-eyed, with males showing 50% red-eyed and 50% white-eyed.

Sex-Linked Genes

• Genes located on sex chromosomes (X or Y) known as sex-linked genes.
• This concept applies to various organisms, including humans, plants, and insects.

Linked Genes

• Each chromosome contains hundreds to thousands of genes.
• Genes that are located on the same chromosome are frequently inherited together, as they function as a single unit during genetic crosses.