Explain the experiments carried out by Morgan in Drosphila to demonstrate linkage
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Thomas Hunt Morgan explained the mechanism of linkage through his studies on the fruit fly Drosophila melanogaster. He studied X-linked genes in Drosophila and saw that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. Morgan and Castle in 1911 proposed Chromosome Theory of Linkage that states: (i) Genes that are physically attached to the same chromosome should travel as a unit through meiosis. This implies that genes present on the same chromosome should act as if they are linked to each other, that is, they are part of the same linkage group. The physical evidence for this was found in sweet peas plant in which genes for two traits—flower color and pollen shape—were linked. (ii) Genes are attached to one another like beads on a string in a linear organization. (iii) Genes present on the same chromosome could be separated during meiosis and new combinations of genes could be formed. This phenomenon is called recombination of genes. (iv) During meiosis, when homologous chromosomes paired, the separated and recombined genes physically exchange of material at a crossover point called chiasma. This phenomena of exchange between paired chromosomes at the chiasma is called crossing over. Except for crossing over, the genes stay in their parental combination. (v) The distance between the linked genes indicates the strength of linkage. Closely spaced genes have stronger linkage than those far apart. Likelihood of crossing over increases with increasing distance. (vi) For any two genes present on different chromosomes, the recombination frequency never exceeds 50%. This implies that the genes are assorted independently.Read more on Sarthaks.com - https://www.sarthaks.com/544169/explain-linkage-recombination-observations-drosophila-melanogaster-crossing-experiment