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Science · 2024 · 4 marks
CBSE 2024 · Region 1 · Set 1 · Q38
Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.(i)When Mendel crossed pea plants with pure tall and pure short characteristics to produce $\displaystyle \mathrm{F}_{1}$ progeny, which two observations were made by him in $\displaystyle \mathrm{F}_{1}$ plants?(ii)Write one difference between dominant and recessive trait.(iii)In a cross with two pairs of contrasting characters RRYY × rryy (Round Yellow) (Wrinkled Green) Mendel observed $\displaystyle 4$ types of combinations in $\displaystyle \mathrm{F}_{2}$ generation. By which method did he obtain $\displaystyle \mathrm{F}_{2}$ generation ? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.Justify the statement : "It is possible that a trait is inherited but may not be expressed."
Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i)
When Mendel crossed pea plants with pure tall and pure short characteristics to produce $\displaystyle \mathrm{F}_{1}$ progeny, which two observations were made by him in $\displaystyle \mathrm{F}_{1}$ plants?
(ii)
Write one difference between dominant and recessive trait.
(iii)
In a cross with two pairs of contrasting characters RRYY × rryy (Round Yellow) (Wrinkled Green) Mendel observed $\displaystyle 4$ types of combinations in $\displaystyle \mathrm{F}_{2}$ generation. By which method did he obtain $\displaystyle \mathrm{F}_{2}$ generation ? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.
Justify the statement : "It is possible that a trait is inherited but may not be expressed."
Marking-scheme solution
In \(\displaystyle \mathrm{F}_{1}\) generation, all plants were tall / No short plants were observed
No medium height plants / No halfway characteristics were observed / Only dominant parental traits were seen and not the mixture of the two.
(ii)
| Dominant trait | Recessive trait |
| Single copy of dominant trait is enough to get it expressed/always expressed | Only expressed when present in pair. |
(iii)
Self-pollination / Self-fertilisation / Selfing of \(\displaystyle \mathrm{F}_{1}\) plants
Ratio - Round Yellow : Wrinkled Green $\displaystyle 9$ : $\displaystyle 1$
Traits are inherited independently.
(B)
If pea plants with yellow seeds are crossed with plants of green seeds, it is found that in \(\displaystyle \mathrm{F}_{1}\) generation all the plants have yellow seeds. When \(\displaystyle \mathrm{F}_{1}\) plants are self-pollinated, it is found that in \(\displaystyle \mathrm{F}_{2}\) generation, plants with yellow seeds and plants with green seeds are obtained. This shows that both the traits are inherited but only one trait is visible in \(\displaystyle \mathrm{F}_{1}\) progeny while the other remains unexpressed.
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.