Biology XII: 5 Prin of Inher & Vari(6 Dihybrid Cross in Drosophila

Dihybrid Cross in Drosophila to Study Linkage and Recombination Linkage and Recombination Thomas Hunt Morgan discovered the basis of variations that sexual reproduction produced. He worked on fruit flies, Drosophila melanogaster. He chose Drosophila because of the following reasons: They were suitable to grow on synthetic medium in laboratory. Their life cycle is complete in two weeks. Single mating produces many progeny flies. Clear differentiation of sexes − Easily distinguishable male and female Hereditary variations clearly visible with low power microscopes Morgan’s experiment Dihybrid cross was carried out on fruit flies. Yellow bodied, white eyed females were crossed with brown bodied, red eyed males. F1 progeny was obtained, which were inter-crossed. F2 progeny was obtained and F2 ratio was observed. F2 ratio was observed to be significantly different from 9:3:3:1 as observed in Mendelian dihybrid cross. Explanation of deviation from Mendelian ratio: Genes involved are located on X chromosome. When two genes are located on the same chromosome, the proportions of parental gene combinations were much higher than those of non-parental. Linkage − Physical association of genes on a chromosome Recombination − Non-parental gene combination Alfred Sturtevant utilised the knowledge of frequency of gene recombination as a measure of physical distance between two genes and to map their position on chromosomes. In this way, genetic maps were prepared, which are extensively used today for genome sequencing projects as in human genome project.