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Biology · 2025 · 5 marks
CBSE 2025 · Region 1 · Set 1 · Q33
Student to attempt either option-(A) or (B): (A) (i) Perform a cross between two sickle cell carriers. What ratio is obtained between carrier,…
Student to attempt either option-(A) or (B) :
(i)
Perform a cross between two sickle cell carriers. What ratio is obtained between carrier, disease free and diseased individuals in $\displaystyle \mathrm{F}_{1}$ progeny ? Name the nitrogenous base substituted, in the haemoglobin molecule in this disease.
(ii)
Explain the difference in inheritance pattern of flower colour in garden pea plant and snap-dragon plant with the help of monohybrid crosses.
Explain with the help of well-labelled diagrams how lac operon operates in E. coli :
(i)
In presence of an inducer.
(ii)
In absence of an inducer.
Marking-scheme solution
(i)
$\displaystyle \star$ Ratio $\displaystyle 2$ : $\displaystyle 1$ : $\displaystyle 1$ (Carrier : Disease free : Diseased)
$\displaystyle \star$ Adenine is substituted by Thymine
(ii)
Inheritance pattern of flower colour in garden pea plant follows Law of Dominance because violet colour is dominant over white colour of flower.
P : WW (Violet flower) X ww (White flower)
Gametes : W, W and w, w
In case of snapdragon the flower colour shows incomplete dominance and all the F1 progeny is of pink colour because red colour is not completely dominant over recessive white colour.
P : RR (Red flower) X rr (White flower)
Gametes : R, R and r, r
(i)
In presence of inducer
(ii)
In absence of inducer
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