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Biology · 2025 · 5 marks
CBSE 2025 · Region 1 · Set 2 · Q33
Student to attempt either option-(A) or (B): (A) (i) Haemophilia and red green colourblindness is usually observed in men. Why? (ii) Perform a…
Student to attempt either option-(A) or (B) :
(i)
Haemophilia and red green colourblindness is usually observed in men. Why ?
(ii)
Perform a cross(es) where haemophilic daughter(s) and haemophilic son(s) are produced in same ratio.
(i)
Where do transcription and translation occur in bacteria and eukaryotes respectively ?
(ii)
Draw a labelled schematic sketch of replication fork of DNA.
(iii)
A DNA segment has a total of $\displaystyle 1000$ nucleotides, out of which $\displaystyle 240$ of them are Adenine containing nucleotides. How many pyrimidine bases this segment possesses ?
Marking-scheme solution
(i)
Both are sex-linked / X-linked recessive disorder
Males usually have only single X chromosome so disease is easily expressed.
(ii)
Cross-$\displaystyle 1$
Ratio $\displaystyle 1$:$\displaystyle 1$ Haemophilic daughter:Haemophilic son
Cross-$\displaystyle 2$
Ratio $\displaystyle 2$ : $\displaystyle 2$ / $\displaystyle 1$ : $\displaystyle 1$ Haemophilic daughter : Haemophilic son
(i)
Transcription in bacteria occurs in cytoplasm of cell
Translation in bacteria occurs in cytoplasm of cell
In Eukaryotes transcription occurs in nucleus, and translation occurs in the cytoplasm.
(ii)
(iii)
Total nucleotides = $\displaystyle 1000$
Adenine = $\displaystyle 240$
$\displaystyle \mathrm{A}=\mathrm{T}$ therefore $\displaystyle \mathrm{T}=240$
$\displaystyle \mathrm{A}+\mathrm{T}=480$
$\displaystyle \mathrm{C}+\mathrm{G}=1000-(\mathrm{A}+\mathrm{T})=1000-480=520$
Since $\displaystyle \mathrm{C}=\mathrm{G}$ Therefore $\displaystyle \mathrm{C}=520 / 2=260$
Total Pyrimidines $\displaystyle =\mathrm{T}+\mathrm{C}$ Therefore $\displaystyle 240+260=500$
All Principles of Inheritance and Variation questions2025 question paperNCERT solutions: Principles of Inheritance and VariationPractice Principles of Inheritance and Variation →
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