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Exercises · Q9

Q.Briefly mention the contribution of T.H. Morgan in genetics.

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T.H. Morgan's fruit fly experiments established the chromosomal theory of inheritance and proved that genes are located on chromosomes in a linear order, founding modern genetics.

Thomas Hunt Morgan transformed genetics from a theoretical science into an experimental one. Working at Columbia University in the early twentieth century, he chose Drosophila melanogaster — the common fruit fly — as his experimental organism. This choice was brilliant: fruit flies are tiny, breed rapidly (a new generation every two weeks), produce hundreds of offspring, and are cheap to maintain in milk bottles in a laboratory.

Morgan's breakthrough came when he discovered a white-eyed male fly among thousands of normal red-eyed flies. This was a spontaneous mutation. When he crossed this mutant male with normal red-eyed females, all the offspring in the first generation had red eyes. But in the second generation, the white-eyed trait reappeared — and strikingly, only in males. This was the first clear evidence of sex-linked inheritance.

Important

Morgan demonstrated that the gene for eye colour in Drosophila is located on the X chromosome, proving that genes physically reside on chromosomes and are not just abstract factors.

He went further. By studying many traits together, Morgan and his students noticed that certain genes tend to be inherited together — they showed linkage. But this linkage was not absolute; sometimes the linked traits separated. Morgan explained this through crossing over, the physical exchange of chromosome segments during meiosis. Crucially, he observed that genes farther apart on a chromosome cross over more frequently than genes close together. …

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