ï»¿ Which one of the following cannot be explained on the basis of Mendel's Law of Dominance?Â  from Biology Principles of Inheritance and Variation Class 12 Nagaland Board

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Which one of the following cannot be explained on the basis of Mendel's Law of Dominance?Â

• the discrete unit controlling a particular character is called a factor

• Out of one pair of factors, one is dominant and the other recessive

• Alleles do not show any blending and both the characters recover as such in F2 generation

• Factors occur in pairs

C.

Alleles do not show any blending and both the characters recover as such in F2 generation

The law of dominance does not occur universally. After Mendel, several cases were recorded by scientists, where a clear deviation from the law of dominance was seen. Such a deviation may be seen in the form of Incomplete dominance or Blending inheritance Co-dominance.Â

Where F1 hybrids exhibited a mixture of blending or character of two parents, the case is considered as that of incomplete dominance blending inheritance. It simply means that two genes of an allelomorphic pair are not related as dominant or recessive, but each of them expresses itself partially.Â In the case of 4 o' clock plant, when plants with red flowers are crossed with plants having white flowers are crossed with plants having a white flower, the F1 hybrids bear a pinkÂ flower. When these pink flowers are self-pollinated, they develop red, pink and white flowers in the ratio of 1: 2:1 respectively.

The law of dominance does not occur universally. After Mendel, several cases were recorded by scientists, where a clear deviation from the law of dominance was seen. Such a deviation may be seen in the form of Incomplete dominance or Blending inheritance Co-dominance.Â

Where F1 hybrids exhibited a mixture of blending or character of two parents, the case is considered as that of incomplete dominance blending inheritance. It simply means that two genes of an allelomorphic pair are not related as dominant or recessive, but each of them expresses itself partially.Â In the case of 4 o' clock plant, when plants with red flowers are crossed with plants having white flowers are crossed with plants having a white flower, the F1 hybrids bear a pinkÂ flower. When these pink flowers are self-pollinated, they develop red, pink and white flowers in the ratio of 1: 2:1 respectively.

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What for symbols AA and Aa stand ?

AA : Homozygous dominant, Aa : Heterozygous dominant.
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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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Name one trait that does not blend.

Sex trait .
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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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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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