Question
Short Answer Question.
Write a note on pleiotropy.
Write a note on pleiotropy.
✓
Answer
1. When a single gene controls two (or more) different traits it is called pleiotropic gene and the phenomenon is called pleiotropy or pleiotropism.
2. The phenotypic ratio is $1: 2$ instead of $3: 1$ because of the death of recessive homozygote.
3. For example, the disease, sickle-cell anaemia, is caused by a gene $Hb ^S$. Normal or healthy gene $Hb ^{ A }$ is dominant.
4. The carriers (heterozygotes $Hb ^A / Hb ^S$ ) show signs of mild anaemia as their RBCs become sickle-shaped i.e. half-moon-shaped only under abnormally low $O _2$ concentration.
5. The homozygotes with recessive gene $Hb ^{ S }$ die of fatal anaemia.
6. 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.
2. The phenotypic ratio is $1: 2$ instead of $3: 1$ because of the death of recessive homozygote.
3. For example, the disease, sickle-cell anaemia, is caused by a gene $Hb ^S$. Normal or healthy gene $Hb ^{ A }$ is dominant.
4. The carriers (heterozygotes $Hb ^A / Hb ^S$ ) show signs of mild anaemia as their RBCs become sickle-shaped i.e. half-moon-shaped only under abnormally low $O _2$ concentration.
5. The homozygotes with recessive gene $Hb ^{ S }$ die of fatal anaemia.
6. 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.
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