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22. Variation And Genetics eLearn.Punjab
SEX LINKAGE

Sex Linkage in Drosophila
Thomas Hunt Morgan (1910) provided experimental evidence in support of chromosomal
theory of heredity through discovery of sex linkage in fruitfly Drosophila.

Drosophila is a very useful organism for genetic studies for many reasons: *
1. The tiny fly is often seen hovering over rotten fruits. It can be easily collected and

cultured on mashed banana and other fruits. It does not need large spacious cages.
It lives happily in ordinary glass bottle of jams and marmalades. It eats yeast that
grows on mashed banana.
2. Male and female Drosophila show sexual dimorphism i.e. these are morphologically
distinct from each other. Male is smaller in size with black rounded abdomen. Female
is larger with pointed abdomen. Male has sex combs on front legs.
3. Drosophila has a generation time of just two weeks. It lays a large number of eggs
which hatch out into fertile offspring. Many generations can be raised in a relatively
short time.
4. 4. Drosophila is perfectly suited for genetic studies. It shows fairly large number of
distinct contrasting traits. Morgan and his colleagues studied pattern of inheritance
of more than 85 traits of Drosophila. Its larvae are excellent material for dissection
for chromosome study. It has only eight chromosomes in four homologous pairs
that can be conveniently studied under a microscope. Its salivary gland cells have
giant chromosomes in their nuclei. These giant chromosomes have characteristic
banding patterns corresponding to genes.
5. 5. The entire genome of Drosophila has been successfully sequenced as part of
human genome project.

Morgan raised cultures of Drosophila flies to study different traits, such as colour of
the eye. Normal fruit flies, the wild type, have bright red eyes. One of his coworkers
Calvin Bridges, observed an unusual white eye mutant male fly. (Fig. 22.25).

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