What Is Genic Balance Theory?
C.B. Bridges in 1922 proposed the Genic Balance Theory for sex determination while working on his experimental model, Drosophila.
Like mammals, XX sex chromosome determines female character and XY as males in Drosophila. However, unlike humans, Y chromosome is not responsible for maleness in Drosophila, as Y chromosome is heterochromatic in nature and thus not active in sex determination.
According to Bridges, sex determination in Drosophila depends on the X/A sex index ratio. Following are the sex index ratios for maleness and female characters:
If X/A = 1.0 it means normal female
If X/A = 0.5, it means normal male
If X/A = <0.5, it means super male
If X/A = 0.5 to 1.0, it means intersex
If X/A = >1.0, it means super female
For example, 3A+XXX: X/A = 3/3 = 1.0 => Normal female
2A+XO: X/A = 1/2 = 0.5 => Normal male
Like mammals, XX sex chromosome determines female character and XY as males in Drosophila. However, unlike humans, Y chromosome is not responsible for maleness in Drosophila, as Y chromosome is heterochromatic in nature and thus not active in sex determination.
According to Bridges, sex determination in Drosophila depends on the X/A sex index ratio. Following are the sex index ratios for maleness and female characters:
If X/A = 1.0 it means normal female
If X/A = 0.5, it means normal male
If X/A = <0.5, it means super male
If X/A = 0.5 to 1.0, it means intersex
If X/A = >1.0, it means super female
For example, 3A+XXX: X/A = 3/3 = 1.0 => Normal female
2A+XO: X/A = 1/2 = 0.5 => Normal male
AIPMT result 2015
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AIPMT test result 2015