Mention the dominant and recessive traits of two characters related with seed and one character related with flower of pea plant. Very often it is experienced that a colour-blind son is born to apparently normal parents. Show with the help of a cross how it happens.
WBBSE
Class X
Life Science
03 (a) Heredity
03 (b) Some Common Genetic Diseases
05 Mark
2025
Here are two seed-related characters commonly used in Mendel’s experiments, showing their dominant and recessive traits clearly.
| Character (Seed Trait) | Dominant Trait | Recessive Trait |
| Seed Shape | Round | Wrinkled |
| Seed Colour | Yellow | Green |
Parents (apparently normal)
- Father: Normal → XNY
- Mother: Normal but carrier → XNXC
Punnett Square
| XN | Y | |
| XN | XNXN (Normal daugther) |
XNY (Normal son) |
| XC | XNXC (Carrier daughter) |
XCY (Colour-blind son) |
Result
- 25% sons are colour-blind
- Parents look normal
- Defective gene comes from the mother
- Son shows the trait because he has only one X chromosome
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