Science Class- 10
Class 10 - Chapter 8: Heredity
Q1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
Answer: (b) TTww
Explanation:
Let:
- T = Tall (dominant)
- t = Short (recessive)
- W = Violet flower (dominant)
- w = White flower (recessive)
The short white parent must have the genotype ttww.
Since all offspring have violet flowers, the tall parent must contribute only the dominant violet allele (W), so its flower genotype is WW.
Almost half the progeny are short, indicating that the tall parent is heterozygous for height (Tt).
Therefore, the genotype of the tall violet parent is:
TtWW
Correct Option: (c) TtWW
Q2. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
No, we cannot conclude whether light eye colour is dominant or recessive from this information alone.
The observation only shows that the trait is inherited from parents to offspring.
To determine whether a trait is dominant or recessive, we need information about its inheritance over several generations and the appearance of the trait in offspring from different parental combinations.
Therefore, the given data is insufficient to determine dominance or recessiveness.
Q3. Outline a project which aims to find the dominant coat colour in dogs.
Aim: To determine the dominant coat colour in dogs.
Procedure:
- Select dogs with two different coat colours, for example black and brown.
- Cross a pure black-coated dog with a pure brown-coated dog.
- Observe the coat colour of all F1 offspring.
- If all F1 offspring show the same coat colour, that colour is likely dominant.
- Allow F1 dogs to breed among themselves.
- Observe the coat-colour ratio in the F2 generation.
- A ratio close to 3:1 supports Mendelian dominance.
Observation Table:
| Generation | Cross | Expected Observation |
|---|---|---|
| P | Black × Brown | Parent Generation |
| F1 | Offspring | All dominant colour |
| F2 | F1 × F1 | Approximately 3:1 ratio |
The coat colour appearing in all F1 offspring is considered the dominant trait.
Q4. How is the equal genetic contribution of male and female parents ensured in the progeny?
During sexual reproduction, both male and female parents produce gametes through meiosis.
Each gamete contains only one set of chromosomes (haploid).
During fertilization, the male gamete (sperm) and female gamete (egg) fuse to form a zygote.
The zygote receives half of its chromosomes from the father and half from the mother.
Chromosome Contribution:
| Parent | Chromosome Contribution |
|---|---|
| Male Parent (Sperm) | 50% |
| Female Parent (Egg) | 50% |
Thus, equal genetic contribution from both parents is ensured in the progeny.