HSC Science (General) 12th Board ExamMaharashtra State Board
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# Solution - Why the Ratio in Pleiotropy is 2 : 1? Explain It with Example. - HSC Science (General) 12th Board Exam - Biology

ConceptDeviations from Mendelism - Incomplete Dominance, Co-dominance, Multiple Alleles and Inheritance of Blood Groups, Pleiotropy

#### Question

Why the ratio in pleiotropy is 2 : 1? Explain it with example.

#### Solution

 Pleiotropic gene is a gene which controls or produces two or more traits or expressions, respectively, and the phenomenon is known as pleiotropy.
 For example, the disease sickle cell anaemia is caused by this phenomenon. The disease is caused by gene HbS.
 In a normal or healthy individual, the gene is HbA, which is dominant.
 A heterozygote is a carrier and shows mild signs of anaemia, and the RBCs become sickle-shaped with a deficiency of oxygen.
 The homozygous recessive individuals however show fatal anaemia and die.
 Hence, if two carriers for sickle cell anaemia mate, the children are formed in the ratio of 1:2:1, with 1 normal, 2 carriers and 1 diseased.
 Because the diseased child dies, the observed ratio of the surviving children is 1:2.
 Thus, pleiotropy shows a 2:1 ratio and not the normal Mendelian 3:1 ratio.

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#### APPEARS IN

2015-2016 (March) (with solutions)
Question 3.1.1 | 3 marks

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Solution for question: Why the Ratio in Pleiotropy is 2 : 1? Explain It with Example. concept: Deviations from Mendelism - Incomplete Dominance, Co-dominance, Multiple Alleles and Inheritance of Blood Groups, Pleiotropy. For the course HSC Science (General)
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