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Science · 2022 · 3 marks
CBSE 2022 · Region 1 · Set 3 · Q11
A red-eyed individual is crossed with a white-eyed individual to produce F_1 progeny with red eyes. When F_1 individuals are intercrossed, F_2…
A red-eyed individual is crossed with a white-eyed individual to produce $\displaystyle \mathrm{F}_{1}$ progeny with red eyes. When $\displaystyle \mathrm{F}_{1}$ individuals are intercrossed, $\displaystyle \mathrm{F}_{2}$ progeny is formed with both red as well as white-eyed individuals.
(a)
How is the dominant trait identified?
(b)
What are recessive traits?
(c)
If $\displaystyle 12$ individuals are produced in $\displaystyle \mathrm{F}_{2}$ generation, then how many white-eyed individuals would be obtained? Calculate the ratio of red-eyed individuals to white-eyed individuals. \[1+\frac{1}{2}+\frac{1}{2}+1 \]
Marking-scheme solution
(a) The F1 progeny is only red eyed individuals. So, the red eye is the dominant trait.
(b) The traits that cannot express themselves in the presence of a dominant trait.
(c) - $\displaystyle 3$ white eyed individuals.
red eyed : white eyed $\displaystyle 3$ : $\displaystyle 1$
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CBSE Class 10 Science past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.