4.4.1 Genic balance in Drosophila
Chapter 3: 4. Luteal or secretory phase · ZOOLOGY · EN medium
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Genic balance mechanisms of sex determination in Drosophila was first studied by C.B. Bridges. In Drosophila , the presence of Y chromosome is essential for the fertility of male sex, but does not determine the male sex. The gene for femaleness is located on the X chromosome and those for maleness are located on the autosomes. When geneticist C.B. Bridges, working with Drosophila , crossed a triploid (3n) female with a normal male, he observed many combinations of autosomes and sex chromosomes in the offspring.
📖 Class 12 Zoology English 2024 Edition www.tntextbooks.in · Page 57
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Genic balance mechanisms of sex determination in Drosophila was first studied by C.B. Bridges. In Drosophila , the presence of Y chromosome is essential for the fertility of male sex, but does not determine the male sex. The gene for femaleness is located on the X chromosome and those for maleness are located on the autosomes.
When geneticist C.B. Bridges, working with Drosophila , crossed a triploid (3n) female with a normal male, he observed many combinations of autosomes and sex chromosomes in the offspring. From his results Bridges in suggested that sex in Drosophila is determined by the balance between the genes for femaleness located on the X chromosomes and those for maleness located on the autosomes. Hence the sex of an individual is determined by the ratio of its X chromosome to that of its autosome sets.
This ratio is termed sex index and is expressed as:
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