Answer in Brief
Short Answer Question.
Write a note on pleiotropy.
Give an account of pleiotropy with a suitable example.
- When a single gene controls two (or more) different traits it is called pleiotropic gene and the phenomenon is called pleiotropy or pleiotropism.
- The phenotypic ratio is 1:2 instead of 3:1 because of the death of recessive homozygote. The disease, sickle-cell anaemia, is caused by a gene HbS.
- Normal or healthy gene HbA is dominant. The carriers (heterozygotes HbA /HbS) show signs of mild anaemia as their RBCs become sickle shaped i.e. half-moon-shaped only under abnormally low O2 concentration.
- The homozygotes with recessive gene HbS die of fatal anaemia.
- Thus, the gene for sickle-cell anaemia is lethal in homozygous condition and produces sickle cell trait in the heterozygous carrier. Two different expressions are produced by a single gene.
Concept: Deviations from Mendel’s Findings
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