12th Botany Chapter-1 Book Back Answer

 

Chapter-2

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Classical Genetics

23.Name the seven contrasting traits of Mendel.

Character	Dominant Trait	Recessive Trait
1. Stem length	Tall	Dwarf
2. Pod shape	Inflated	Constricted
3. Seed shape	Round	Wrinkled
4. Seed colour	Yellow	Green
5. Flower position	Axial	Terminal
6. Flower colour	Purple	White
7. Pod colour	Green	Yellow

24.What is meant by true breeding or pure breeding lines / strains?

The phenomenon of continuous self pollination and traits inheritance from parent to offspring is called true breeding or pure breeding lines.

25.Give the name of the scientists who rediscovered Mendelism.

1. Hugo de vries (Holland)

2. Carl Correns (Germany)

3. Tschermak (Austria)

26.What is Back cross?

i) F₁ hybrid crossed with any one of the parental genome is called back cross.

ii) Back cross are two types, 1. Dominant back cross

2. Recessive back cross

27.Define Genetics.

Genetics is a branch of biology which deals with the mechanism of transmission of characters from parents to offspring. The term Genetics was introduced by W.Bateson.

28.What are multiple alleles?

Multiple alleles are a set of three or more genes controlling the same character located on the same locus of homologous chromosome.

29.What are the reasons for Mendel’s successes in his breeding experiment?

1. He applied mathematics and statistical methods in Biology.

2. His experiments were carefully planned.

3. He used large samples.

30.Explain the law of dominance in Monohybrid cross.

• In a dissimilar pair of factors, one is dominant and other is recessive.

• This law is explained in Mendel’s Monohybrid cross.

Parental Generation : Tall X Dwarf

(TT) (tt)

Gametes: (T) (t)

F₁ Generation: Heterozygous Tall

(Tt)

F₂ Generation: Tt X Tt

Gametes	T	t
T	TT (Homozygous Tall)	Tt (Heterozygous Tall)
t	Tt (Heterozygous Tall)	tt (Homozygous dwarf)

Phenotypic Ratio: 3 (Tall) : 1 (Dwarf)

Genotypic Ratio:

1(Homozygous tall): 2 (Heterozygous tall): 1(Homozygous dwarf)

31.Differentiate incomplete dominance and codominance.

Incomplete Dominance	Codominance
1. One allele is not completely dominant to another allele	1. Two alleles are expressed in the heterozygous individual.
2. Example: 4’O clock plant (Mirabilis jalapa)	2. Example: Camellia.

32.What is meant by cytoplasmic inheritance?

Cytoplasmic organelles such as chloroplast and mitochondria act as inheritance vectors, It is called Cytoplasmic inheitance.

Example: 4’O clock plant.

33.Describe Dominant epistasis with an example.

• The prevention of the expression of one gene by another non-allelic gene is called Epistasis.

• The inhibiting gene is called epistatic gene. The inhibited gene is called hypostatic gene.

• Epistasis is of two types namely, dominant epistasis and recessive epistasis.

• The Prevention of an expression of a gene by a dominant non-allelic gene is called dominant epistasis.

• The prevention of the expression of a gene by a recessive non-allelic gene is called recessive epistasis.

• Summer squash white fruit plant (Wwgg) is crossed with yellow fruit plant (wwGG). It will produce heterozygous (WwGg) white fruit in F₁ generation.

• When the F₁ generation heterozygous plants are self crossed, it will produce in the phenotypic ratio of 12 White, 3 Yellow and 1 Green in F₂ generation.

• So, the dominant allele ‘’W’’ is suppress or mask the character of other non-allelic genes.

Parental generation: White Fruit X Yellow Fruit

(WWgg) (wwGG)

Gametes: (Wg) (wG)

F₁ Generation: White fruit

(WwGg)

F₂ Generation: WwGg X WwGg

Gametes	WG	Wg	wG	wg
WG	WWGG (White)	WWGg (White)	WwGG (White)	WwGg (White)
Wg	WWGg (White)	WWgg (White)	WwGg (White)	Wwgg (White)
wG	WwGG (White)	WwGg (White)	wwGG (Yellow)	wwGg (Yellow)
wg	WwGg (White)	Wwgg (White)	wwGg (Yellow)	Wwgg (Green)

Phenotypic Ratio: 12 (White) : 3 (Yellow) : 1 (Green)

34.Explain polygenic inheritance with an example.

• A group of genes that together determine the character of an organism is called polygenic inheritance.

• The first polygenic inheritance experiment was demonstrated by H.Nilson-Ehle (1909) in wheat kernels.

• Kernel colour is controlled by two genes with two alleles.

• Red kernel colour was dominant to white kernel.

• Dark red kernel plant ( R₁R₁R₂R₂ ) is crossed with white kernal plant (r₁r₁r₂r₂). It will produce heterozygous (R₁r₁R₂r₂) medium red plant in F₁ generation.

• When F₁ generation heterozygous plants are self crossed, It will produce the phenotypic ratio of 15 red kernel and 1 white kernel in F₂ generation.

Parental generation: Dark red X White

(R₁R₁R₂R₂) (r₁r₁r₂r₂)

Gametes: (R₁R₂) (r₁r₂)

F₁ Generation: Medium size

(R₁r₁R₂r₂)

F₂ Generation: R₁r₁R₂r₂ X R₁r₁R₂r₂

Gametes	R1R2	R1r2	r1R2	r1r2
R1R2	R1R1R2R2 (Dark red)	R1R1R2r2 (Medium-dark red)	R1r1R2R2 (Medium-red dark)	R1r1R2r2 (Medium red)
R1r2	R1R1R2r2 (Medium-dark red)	R1R1r2r2 (Medium red)	R1r1R2r2 (Medium red)	R1r1r2r2 (Light red)
r1R2	R1r1R2R2 (Medium-dark red)	R1r1R2r2 (Medium red)	r1r1R2R2 (Medium red)	r1r1R2r2 (Light red)
r1r2	R1r1R2r2 (Medium red)	R1r1r2r2 (Light red)	r1r1R2r2 (Light red)	r1r1r2r2 (White)

Phenotypic Ratio: 15 (red) : 1 (White)

35.Differentiate continuous variation and discontinuous variation.

Continuous Variation	Discontinuous Variation
1. This is limited variations.	1. These variations are based on environmental and genetic factors.
2.Characteristic are controlled by one or two major genes.	2. It is a continuous change without any break.
3. It is genetically determined by inheritance factors.	3. It is determined by many genes.
4. It is unaffected by environmental conditions.	4. It is affected by environmental conditions
5. Example: Style length in Primula.	5. Example: Human height and skin colour.