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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation3 Marks
Question
Explain the inheritance of Sickle Cell anaemia.
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Answer

Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). The disease is controlled by a single pair of allele, $Hb ^{ A }$ and $Hb ^{ S }$. Out of the three possible genotypes only homozygous individuals for $Hb ^{ S }\left( Hb ^{ S } Hb ^{ S }\right)$ show the diseased phenotype. Heterozygous $\left( Hb ^{ A } Hb ^{ S }\right)$ individuals appear apparently unaffected but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny, thus exhibiting sicklecell trait.
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