Question

Three Mark Questions :
During his studies on genes in Drosophila that were sex linked, T. H. Morgan found $F_2$ population phenotypic ratios deviated from expected 9 : 3 :3 :1. Explain the conclusion he arrived at.

Answer 1

Morgan’s experiment:- Dihybrid cross was carried out on fruit flies. Yellow bodied, white-eyed females were crossed with brown bodied, red-eyed males. F progeny was obtained, which were inter-crossed. F progeny was obtained and the F ratio was observed. F 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.