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Science · 2023 · 4 marks
CBSE 2023 · Region 4 · Set 2 · Q38
The most obvious outcome of the reproductive process is the generation of individuals of similar design, but in sexual reproduction they may not be…
The most obvious outcome of the reproductive process is the generation of individuals of similar design, but in sexual reproduction they may not be exactly alike. The resemblances as well as differences are marked. The rules of heredity determine the process by which traits and characteristics are reliably inherited. Many experiments have been done to study the rules of inheritance.
(i)
Why an offspring of human being is not a true copy of his parents in sexual reproduction?
(ii)
While performing experiments on inheritance in plants, what is the difference between $\displaystyle \mathrm{F}_{1}$ and $\displaystyle \mathrm{F}_{2}$ generation?
(iii)
Why do we say that variations are useful for the survival of a species over time?
Study Mendel's cross between two plants with a pair of contrasting characters.
He observed $\displaystyle 4$ types of combinations in $\displaystyle \mathrm{F}_{2}$ generation. Which of these were new combinations? Why do new features which are not present in the parents, appear in $\displaystyle \mathrm{F}_{2}$ generation?
| RRYY | × | rryy |
| Round Yellow | Wrinkled Green |
Marking-scheme solution
(i) Sexual reproduction involves the fusion of male and female gametes, which combines to the characters of both parents and cause variation.
(ii)| \(\displaystyle \mathbf{F}_{\mathbf{1}}\) generation | \(\displaystyle \mathbf{F}_{\mathbf{2}}\) generation |
| - In \(\displaystyle \mathrm{F}_{1}\) generation only the dominant traits are expressed. | |
| - It refers to the offspring/ plants resulting immediately from a cross between the first set of parents. | - In \(\displaystyle \mathrm{F}_{2}\) generation both dominant and recessive traits are expressed. |
| - It refers to the offspring/plants resulting from a cross among the plants of \(\displaystyle \mathrm{F}_{1}\) generation. |
(iii)(A)
Because if a niche of population of organisms is altered, the whole population could be wiped out. However, if variation is present in this population they have some chance of survival.
[Alternate answer] If there is a population of bacteria living in temperate waters and if water temperature were to be increased by global warming, most of the bacteria would die, but a few variants resistant to heat would survive and grow further. Thus, variations are useful for survival of species over time.
(iii) (B) • Wrinkled, yellow Round, green
If two or more traits are involved, their genes are independently inherited irrespective of the combination present in parents.
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.