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.
- For example, 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 conditions and produces sickle cell trait in the heterozygous carrier. Two different expressions are produced by a single gene.
Graphical representation of pleiotropy
- A marriage between two carriers will produce normal, carriers and sickle-cell anaemic children in a 1: 2: 1 ratio.
Concept: Deviations from Mendel’s Findings
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