Differentiate between the following:

(a) Dominance and Recessive

(b) Homozygous and Heterozygous

(c) Monohybrid and Dihybrid

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Solution

(a) Dominant and recessive

Dominant Recessive

1. The dominant allele is able to express itself even in the presence
of the recessive allele.
The recessive allele is unable to express its effect in the presence
of the dominant allele.

2. It does not require another similar allele to produce its effect on the phenotype, e.g., Tt is tall.
It produces its phenotypic effect only in the

presence of a similar allele, e.g., tt is dwarf.

Dominant allele or enzyme for expressing its

effects, e.g., red colour of the flower in pea.

The recessive allele forms an incomplete or defective polypeptide or

enzyme so that the expression consists of the absence of the effect of dominant allele, e.g., with flower colour in pea.

(b) Homozygous and Heterozygous

Homozygous Heterozygous

1. It is pure for a trait and breeds true i.e., gives rise to similar homozygous individuals Heterozygous individual is seldom pure and produces offspring with different genotypes on selfing, e.g., TT, Tt and tt on selfing of Tt individuals.

2. Both the alleles of a trait are similar, e.g., TT, tt. It carries dissimilar alleles, e.g., Tt.

3. Homozygous individual can carry either dominant or recessive alleles but not both. Heterozygous individual has both dominant and recessive alleles.

4. It produces one type of gametes. It produces two type of gametes.

5. It does not show extra vigour. The individual can show extra vigour called hybrid vigour or heterosis.

(c) Monohybrid and Dihybrid

Monohybrid Dihybrid

1. It is a cross between two pure organisms in order to study the inheritance of a single pair of alleles. It is a cross between two pure organisms of a species in order to study the inheritance of two pairs of alleles belonging to two different characters.

2. It produces a phenotypic monohybrid ratio of 3:1 in F2 generation. It produces a phenotypic dihybrid ratio of 9:3:3:1 in F2 generation.

3. It produces a genotypic ratio of 1:2:1 in F2. It produces the genotypic ratio of 1:2:1:2:4:2:1:2:1 in F2.

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Differentiate between the following −

(a) Dominance and Recessive

(b) Homozygous and Heterozygous

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	Dominant	Recessive
1.	The dominant allele is able to express itself even in the presence of the recessive allele.	The recessive allele is unable to express its effect in the presence of the dominant allele.
2.	It does not require another similar allele to produce its effect on the phenotype, e.g., Tt is tall.	It produces its phenotypic effect only in the presence of a similar allele, e.g., tt is dwarf.
	Dominant allele or enzyme for expressing its effects, e.g., red colour of the flower in pea.	The recessive allele forms an incomplete or defective polypeptide or enzyme so that the expression consists of the absence of the effect of dominant allele, e.g., with flower colour in pea.

	Homozygous	Heterozygous
1.	It is pure for a trait and breeds true i.e., gives rise to similar homozygous individuals	Heterozygous individual is seldom pure and produces offspring with different genotypes on selfing, e.g., TT, Tt and tt on selfing of Tt individuals.
2.	Both the alleles of a trait are similar, e.g., TT, tt.	It carries dissimilar alleles, e.g., Tt.
3.	Homozygous individual can carry either dominant or recessive alleles but not both.	Heterozygous individual has both dominant and recessive alleles.
4.	It produces one type of gametes.	It produces two type of gametes.
5.	It does not show extra vigour.	The individual can show extra vigour called hybrid vigour or heterosis.

	Monohybrid	Dihybrid
1.	It is a cross between two pure organisms in order to study the inheritance of a single pair of alleles.	It is a cross between two pure organisms of a species in order to study the inheritance of two pairs of alleles belonging to two different characters.
2.	It produces a phenotypic monohybrid ratio of 3:1 in F2 generation.	It produces a phenotypic dihybrid ratio of 9:3:3:1 in F2 generation.
3.	It produces a genotypic ratio of 1:2:1 in F2.	It produces the genotypic ratio of 1:2:1:2:4:2:1:2:1 in F2.