Sometimes a gene which carries major disadvantages in homozygous state confers an advantage in heterozygous condition. explain by giving suitable example.
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Most of the times, the defective genes are recessive in nature, thus when it's homozygous, the defective characteristics are shown by the subject.
When in heterozygous state, the dominant gene was expressed and the subject with this heterozygous allele, acts as a carrier instead of being affected.
The most common example is sickle cell anaemia. The dominant gene A forms a heterozygous allele with affected S gene. The people with this allele becomes a carrier. Whereas, one with a homozygous SS allele suffers from the disease.
If the parents are carriers with AS alleles in their body, there are 25% chances to have diseased kid, 25% chance to have unaffected kid and 50% chance to have an unaffected but carrier kid.
A Punnett square is drawn.
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