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Principles of Inheritance and Variation

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

Sickle cell anaemia has not been eliminated from the African population because

• it is controlled by recessive genes

• it is not a fatal disease

• it provides immunity against malaria

• it is controlled by dominant genes

C.

it provides immunity against malaria

Sickle cell anaemia (in which RBCs become sickle shaped and stiff) is a genetic disorder that is autosomal and linked to a recessive allele. It has not been eliminated from the african population because it provides immunity against malaria. People who are heterozygous for sickle allele are much less susceptible for falciparum malaria which is one of the main causes of illness and death in them. Thus, the sickle cell allele is maintained at high levels in population where falciparum malaria is common.

Sickle cell anaemia (in which RBCs become sickle shaped and stiff) is a genetic disorder that is autosomal and linked to a recessive allele. It has not been eliminated from the african population because it provides immunity against malaria. People who are heterozygous for sickle allele are much less susceptible for falciparum malaria which is one of the main causes of illness and death in them. Thus, the sickle cell allele is maintained at high levels in population where falciparum malaria is common.

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Give one example of genetic trait for each of the following in humans : (i) Lethality (ii) Multiple allelism.

(i) Lethality : Sickle cell anaemia.

(ii) Multiple allelism : ABO blood groups.

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Mention the phenomenon of pleiotropy by giving an example.

Pleiotropy. When one gene controls more than one phenotypic character it is termed as pleiotropy.

Example : Sickle cell anaemia.

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Name one trait that does not blend.

Sex trait .
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Name the plant that shows incomplete dominance in respect of the colour of its flower.

The plany which shoes incomplete dominace in respect of the colour of its flower is -

Snapdragron ( Antirrhinum majus)

Or

Mirabilis jalapa (Four-O- Clock plant ).
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What for symbols AA and Aa stand ?

AA : Homozygous dominant, Aa : Heterozygous dominant.
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