CBSE 2025 · Region 6 · Set 2 · Q25 · 3 marks
Answer the following questions with respect to the sex determination mechanism in birds :(a)Name the type of heterogamety observed in most birds.(b)If the birds have $\displaystyle 18$ pairs of autosomal chromosomes and a pair of sex chromosomes, fill in the blanks (i), (ii), (iii) and (iv) in the table given below. (Use symbols Z and W for sex chromosomes.) Total number of autosomes (in a diploid cell) Type of sex chromosomes (in a diploid cell) Male bird (i) $\displaystyle \_\_\_\_$ (ii) $\displaystyle \_\_\_\_$ Female bird (iii) $\displaystyle \_\_\_\_$ (iv) $\displaystyle \_\_\_\_$
Answer the following questions with respect to the sex determination mechanism in birds :
(a)
Name the type of heterogamety observed in most birds.
(b)
If the birds have $\displaystyle 18$ pairs of autosomal chromosomes and a pair of sex chromosomes, fill in the blanks (i), (ii), (iii) and (iv) in the table given below. (Use symbols Z and W for sex chromosomes.)
| Total number of autosomes (in a diploid cell) | Type of sex chromosomes (in a diploid cell) | |
| Male bird | (i) $\displaystyle \_\_\_\_$ | (ii) $\displaystyle \_\_\_\_$ |
| Female bird | (iii) $\displaystyle \_\_\_\_$ | (iv) $\displaystyle \_\_\_\_$ |
Marking-scheme solution
(a)
female heterogamety/ ZW
(i)
Male bird-$\displaystyle 36$
(ii)
ZZ
(iii)
Female bird -$\displaystyle 36$
(iv)
ZW
Principles of Inheritance and VariationSex DeterminationApplyshort_answereasy
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CBSE Class 12 Biology past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.