Name: Cracking the Code: Human Genome Project
Uploaded: 2019-07-19
Duration: 9 min 20 s
Description: Human Genome Project is to sequence the entire human genome containing 3 x 10^9 bp. This application of genetic engineering and bioinformatics took 13 long y...

Question

Describe the Genic Balance Theory of sex determination.

Accepted Answer

The Genic Balance Theory of determination of sex was proposed by Bridges while working on Drosophila. This theory was devised to explain the mechanics of sex determination in Drosophila melanogaster. According to his concept, the sex of an individual is determined by the ‘balance’ between the genes for femaleness located on the X-chromosome and those for maleness located on the ‘autosomes’. Hence, the sex of an individual is determined by the ratio of number of its X chromosomes and that of its autosomal sets, the ‘Y’ chromosome taking no part in the determination of the sex. The ratio is termed as sex index and is expressed as follows.

Sex index = Number of X chromosomes / Number of sets of autosomes (X/A)

Bridges studied the offspring resulting from the non-disjunction of X- chromosomes during meiosis in females. Non-disjunction (not coming apart) is the failure of paired chromosomes to segregate or separate during the anaphase stage of the first or second meiotic divisions. The result is the production of aberrant gametes with abnormal numbers of chromosomes.

Describe the Genic Balance Theory of sex determination.

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