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

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation4 Marks
Question
Explain the causes, inheritance pattern, symptoms of two Mendelian genetic disorders.
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Answer

Two mendelian disorder are:
  1. Sickle cell disease is a genetic disease which is caused due to molecular mutation of gene Hb on chromosome 11 which produces the beta chain of adult hemoglobin. The mutated gene Hbs produces sickle cell haemoglobin.The 6th amino acid in the beta chain of normal haemoglobin is glutamic acid, in sickle cell haemoglobin this amino acid is replaced by valine. The children that are homozygous produce rigid chains. When oxygen level of the blood drops below a certain level, RBC undergoes sickling. Such cells do not transport oxygen efficiently, they are removed by spleen causing severe anaemia. Sickle cell is an autosomal linked disease in which both male and female progenies can be equally affected.
  2. Haemophilia is a sex-linked disorder. In haemophilia, the blood fails to clot when exposed to air and even a small skin injury results in continuous bleeding and can lead to death from the loss of blood. The recessive X linked gene for haemophilia shows characteristic criss-cross inheritance. It's a single gene in male results and disease haemophilia, where is a woman needs two such genes for the same.

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