CBSE 2025, Set 1

Question

Perform a cross between two sickle cell carriers. What ratio is obtained between carrier, disease free and diseased individuals in $F_1$ progeny? Name the nitrogenous base substituted in the haemoglobin molecule in this disease.

Edvaya · Accepted Answer

The correct answer is Subjective. **SOLUTION** **The Cross:** Parents: $Hb^A Hb^S$ (Carrier) $	imes$ $Hb^A Hb^S$ (Carrier) Gametes: $(Hb^A)$, $(Hb^S)$ and $(Hb^A)$, $(Hb^S)$ $F_1$ Progeny: * $Hb^A Hb^A$ (Unaffected/Disease Free) * $Hb^A Hb^S$ (Carrier) * $Hb^A Hb^S$ (Carrier) * $Hb^S Hb^S$ (Affected/Diseased) **Ratio:** The obtained ratio is **$2 : 1 : 1$** (Carrier : Disease free : Diseased). **Base Substitution:** In sickle cell anemia, the defect is caused by a point mutation where the nitrogenous base **Adenine is substituted by Thymine** in the DNA coding strand (resulting in Glutamic acid being replaced by Valine at the sixth position of the beta-globin chain).

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Biology > Reproduction And Genetics > Principles Of Inheritance And Variation

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