Question 2: Differentiate between the following −
(a) Dominance and Recessive
(b) Homozygous and Heterozygous
(c) Monohybrid and Dihybrid.
Answer:
(a) Dominance and Recessive
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Dominance
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Recessive
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1.
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A dominant factor or allele expresses itself in the presence or absence of a recessive factor.
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A recessive trait is able to express itself only in the absence of a dominant factor.
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2.
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For example, tall plant, round seed, violet flower, etc. are dominant traits in a pea plant.
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For example, dwarf plant, wrinkled seed, white flower, etc. are recessive traits in a pea plant.
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(b) Homozygous and Heterozygous
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Homozygous
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Heterozygous
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1.
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It contains two similar alleles for a particular trait.
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It contains two different alleles for a particular trait.
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2.
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Genotype for homozygous possess either dominant or recessive, but never both the alleles. For example, RR or rr
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Genotype for heterozygous possess both dominant and recessive alleles. For example, Rr
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3.
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It produces only one type of gamete.
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It produces two different kinds of gametes.
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(c) Monohybrid and Dihybrid
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Monohybrid Cross
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Dihybrid Cross
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1.
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Monohybrid Cross involves cross between parents, which differs in only one pair of contrasting characters.
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Dihybrid Cross involves cross between parents, which differs in two pairs of contrasting characters.
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2.
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For example, the cross between tall and dwarf pea plant is a monohybrid cross.
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For example, the cross between pea plants having yellow wrinkled seed with those having green round seeds is a dihybrid cross.
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