Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

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Tamilnadu Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Samacheer Kalvi 12th Bio Botany Classical Genetics Text Book Back Questions and Answers

Question 1.
Extra nuclear inheritance is a consequence of presence of genes in __________
(a) Mitrochondria and chloroplasts
(b) Endoplasmic reticulum and mitrochondria
(c) Ribosomes and chloroplast
(d) Lysosomes and ribosomes
Answer:
(a) Mitrochondria and chloroplasts

Question 2.
In order to find out the different types of gametes produced by a pea plant having the genotype AaBb, it should be crossed to a plant with the genotype __________
(a) aaBB
(b) AaBB
(c) AABB
(d) aabb
Answer:
(d) aabb

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 3.
How many different kinds of gametes will be produced by a plant having die genotype AABbCC?
(a) Three
(b) Four
(c) Nine
(d) Two
Answer:
(d) Two

Question 4.
Which one of the following is an example of polygenic inheritance?
(a) Flower colour in MirabilisJalapa
(b) Production of male honey bee
(c) Pod shape in garden pea
(d) Skin Colour in humans
Answer:
(d) Skin Colour in humans

Question 5.
In Mendel’s experiments with garden pea, round seed shape (RR) was dominant over wrinkled seeds (rr), yellow cotyledon (YY) was dominant over green cotyledon (yy). What are the expected phenotypes in the F2 generation of the cross RRYY xrryy?
(a) Only round seeds with green cotyledons
(b) Only wrinkled seeds with yellow cotyledons
(c) Only wrinkled seeds with green cotyledons
(d) Round seeds with yellow cotyledons an wrinkled seeds with yellow cotyledons
Answer:
(d) Round seeds with yellow cotyledons an wrinkled seeds with yellow cotyledons

Question 6.
Test cross involves __________
(a) Crossing between two genotypes with recessive trait
(b) Crossing between two F1 hybrids
(c) Crossing the F1 hybrid with a double recessive genotype
(d) Crossing between two genotypes with dominant trait
Answer:
(c) Crossing the F1 hybrid with a double recessive genotype

Question 7.
In pea plants, yellow seeds are dominant to green. If a heterozygous yellow seed pant is crossed with a green seeded plant, what ratio of yellow and green seeded plants would you expect in generation?
(a) 9:3
(b) 1:3
(c) 3:1
(d) 50:50
Answer:
(d) 50:50

Question 8.
The genotype of a plant showing the dominant phenotype can be determined by __________
(a) Back cross
(b) Test cross
(c) Dihybrid cross
(d) Pedigree analysis
Answer:
(b) Test cross

Question 9.
Select the correct statement from the ones given below with respect to dihybrid cross
(a) Tightly linked genes on the same chromosomes show very few combinations
(b) Tightly linked genes on the same chromosomes show higher combinations
(c) Genes far apart on the same chromosomes show very few recombinations
(d) Genes loosely linked on the same chromosomes show similar recombinations as the tightly I linked ones
Answer:
(a) Tightly linked genes on the same chromosomes show very few combinations

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 10.
Which Mendelian idea is depicted by a cross in which the F1 generation resembles both the parents
(a) Incomplete dominance
(b) Law of dominance
(c) Inheritance of one gene
(d) Co-dominance
Answer:
(d) Co-dominance

Question 11.
Fruit colour in squash is an example of __________
(a) Recessive epistasis
(b) Dominant epistasis
(c) Complementary genes
(d) Inhibitory genes
Answer:
(b) Dominant epistasis

Question 12.
In his classic experiments on Pea plants, Mendel did not use __________
(a) Flowering position
(b) Seed colour
(c) Pod length
(d) Seed shape
Answer:
(c) Pod length

Question 13.
The epistatic effect, in which the hybrid cross 9:3:3:1 between AaBb Aabb is modified as
(a) Dominance of one allele on another allele of both loci
(b) Interaction between two alleles of different loci
(c) Dominance of one allele to another alleles of same loci
(d) Interaction between two alleles of some loci
Answer:
(b) Interaction between two alleles of different loci

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 14.
In a test cross involving F1 dihybrid flies, more parental type offspring were produced than the recombination type offspring. This indicates __________
(a) The two genes are located on two different chromosomes
(b) Chromosomes failed to separate during meiosis
(c) The two genes are linked and present on the some chromosome
(d) Both of the characters are controlled by more than one gene
Answer:
(c) The two genes are linked and present on the some chromosome

Question 15.
The genes controlling the seven pea characters studied by Mendel are known to be located on h6w many different chromosomes?
(a) Seven
(b) Six
(c) Five
(d) Four
Answer:
(a) Seven

Question 16.
Which of the following explains how progeny can posses the combinations of traits that none
of the parent possessed?
(a) Law of segregation
(b) Chromosome theory
(c) Law of independent assortment
(d) Polygenic inheritance
Answer:
(d) Polygenic inheritance

Question 17.
“Gametes are never hybrid”. This is a statement of __________
(a) Law of dominance
(b) Law of independent assortment
(c) Law of segregation
(d) Law of random fertilization
Answer:
(c) Law of segregation

Question 18.
Gene which suppresses other genes activity but does not lie on the same locus is called as __________
(a) Epistatic
(b) Supplement only
(c) Hypostatic
(d) Codominant
Answer:
(c) Hypostatic

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 19.
Pure tall plants are crossed with pure dwarf plants. In the F1 generation, all plants were tall. These tall plants of generation were selfed and the ratio of tall to dwarf plants obtained was 3:1. This is called __________
(a) Dominance
(b) Inheritance
(c) Codominance
(d) Heredity
Answer:
(a) Dominance

Question 20.
The dominant epistatis ratio is _________
(a) 9:3:3:1
(b) 12:3:1
(c) 9:3:4
(d) 9:6:1
Answer:
(b) 12:3:1

Question 21.
Select the period for Mendel’s hybridization experiments.
(a) 1856 – 1863
(b) 1850 – 1870
(c) 1857-1869
(d) 1870 – 1877
Answer:
(a) 1856 – 1863

Question 22.
Among the following characters which one was not considered by Mendel in his experimentation pea?
(a) Stem – Tall or dwarf
(b) Trichomal glandular or non-glandular
(c) Seed – Green or yellow
(d) Pod – Inflated or constricted
Answer:
(b) Trichomal glandular or non-glandular

Question 23.
Name the seven contrasting traits of Mendel.
Answer:
Plant Height, Seed Shape, Cotyledon colour, Flower colour, Pod colour, Pod form, Flower position

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 24.
What is meant by true breeding or pure breeding lines / strain?
Answer:
A true breeding lines (Pure-breeding strains) means it has undergone continuous self pollination having stable trait inheritance from parent to offspring. Matings within pure breeding lines produce offsprings having specific parental traits that are constant in inheritance and expression for many generations. Pure line breed refers to homozygosity only.

Question 25.
Give the names of the scientists who rediscovered Mendelism.
Answer:
Mendel’s experiments were rediscovered by three biologists, Hugo de Vries of Holland, Car Correns of Germany and Erich von Tschermak of Austria.

Question 26.
What is back cross?
Answer:
Back cross is a cross of F1 hybrid with any one of the parental genotypes. The back cross is of two types; they are dominant back cross and recessive back cross. It involves the cross between the F1 off spring with either of the two parents.

Question 27.
Define Genetics.
Answer:
“Genetics” is the branch of biological science which deals with the mechanism of transmission of characters from parents to offsprings. The term Genetics was introduced by W. Bateson in 1906.

Question 28.
What are multiple alleles?
Answer:
Three or more alternative forms of a gene that occupy the same locus and control the expression of a single trait.
E.g : ABO blood group

Question 29.
What are the reasons for Mendel’s successes in his breeding experiment?
Answer:
Mendel was successful because:

  1. He applied mathematics and statistical methods to biology and laws of probability to his breeding experiments.
  2. He followed scientific methods and kept accurate and detailed records that include quantitative data of the outcome of his crosses.
  3. His experiments were carefully planned and he used large samples.
  4. The pairs of contrasting characters which were controlled by factor (genes) were present on separate chromosomes.
  5. The parents selected by Mendel were pure breed lines and the purity was tested by self
    crossing the progeny for many generations.

Question 30.
Explain the law of dominance in monohybrid cross.
Answer:
Law of dominance states that the offsprings of an individual with contrasting (dissimilar) traits will only express the dominant trait in F1 generation and both the characters are expressed in F2 generation. This law also explains the proportion of 3 : 1 ratio in F2 generation.

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 31.
Differentiate incomplete dominance and codominance.
Answer:
Incomplete Dominance:

  1. In incomplete dominance, neither of the allele is not completely dominant to another allele rather combine and produce new trait
  2. New phenotype is formed due to character blending (not alleles)
  3. Example : Pink flowers of Mirabilis Jalapa

Co-dominance:

  1. In co-dominance, both the alleles in heterozygote are dominant and the traits are equally expressed (joint expression)
  2. No formation of new phenotype rather both dominant traits are expressed, conjointly
  3. Example: Red and white flowers of camellia

Question 32.
What is meant by cytoplasmic inheritance
Answer:
DNA is the universal genetic material. Genes located in nuclear chromosomes follow Mendelian inheritance. But certain traits are governed either by the chloroplast or mitochondrial genes. This phenomenon is known as extra nuclear inheritance. It is a kind of Non-Mendelian inheritance. Since it involves cytoplasmic organelles such as chloroplast and mitochondrion that act as inheritance vectors, it is also called Cytoplasmic inheritance.

Question 33.
Describe dominant epistasis with an example.
Answer:
Dominant Epistasis – It is a gene interaction in which two alleles of a gene at one locus interfere and suppress or mask the phenotypic expression of a different pair of alleles of another gene at another locus. The gene that suppresses or masks the phenotypic expression of a gene at another locus is known as epistatic.

The gene whose expression is interfered by non-allelic genes and prevents from exhibiting its character is known as hypostatic. When both the genes are present together, the phenotype is determined by the epistatic gene and not by the hypostatic gene.

In the summer squash the fruit colour locus has a dominant allele ‘W’ for white colour and a recessive allele ‘w’ for coloured fruit. ‘W’ allele is dominant that masks the expression of any colour.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics
Dominant epistasis in summer squash

In another locus hypostatic allele ‘G’ is for yellow fruit and its recessive allele ‘g’ for green fruit. In the first locus the white is dominant to colour where as in the second locus yellow is dominant to green. When the white fruit with genotype WWgg is crossed with yellow fruit with genotype wwGG, the F1 plants have white fruit and are heterozygous (WwGg). When F1 heterozygous plants are crossed.

they give rise to F2 with the phenotypic ratio of 12 white : 3 yellow : 1 green.Since W is epistatic to the alleles ‘G’ and ‘g’, the white which is dominant, masks the effect of yellow or green. Homozygous recessive ww genotypes only can give the coloured fruits (4/16). Double recessive ‘wwgg’ will give green fruit (1/16). The Plants having only ‘G’ in its genotype (wwGg or wwGG) will give the yellow fruit(3/l 6).

Question 34.
Explain polygenic inheritance with an example.
Answer:
Polygenic inheritance – Several genes combine to affect a single trait. A group of genes that together Dark Red determine (contribute) a characteristic of an organism is called polygenic inheritance. It gives explanations to the inheritance of continuous traits which are compatible with Mendel’s Law. The first experiment on polygenic inheritance was demonstrated by Swedish Geneticist H.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 2
Nilsson-Ehle (1909) in wheat kernels. Kernel colour is controlled by two genes each with two alleles, one with red kernel colour was dominant to white. He crossed the two pure breeding wheat varieties dark red and a white. Dark red genotypes F1 generation R1R1R2R2 and white genotypes are r1r1r2r2 – F1 generation medium red were obtained with the genotype R1r1R2r2. F1 wheat plant produces
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics
four types of gametes R1R2, R1r2, r,1r2. The intensity of the red colour is determined by the number of R genes in the F2 generation. Four R genes: A dark red kernel colour is obtained. Three R genes: Medium – dark red kernel colour is obtained. Two R genes: Medium-red kernel colour is obtained. One R gene: Light red kernel colour is obtained. Absence of R gene: Results in White kernel colour.

The R gene in an additive manner produces the red kernel colour. The number of each phenotype is plotted against the intensity of red kernel colour which produces a bell shaped curve. This represents the distribution of phenotype.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 4
Conclusion: Finally the loci that was studied by Nilsson – Ehle were not linked and the genes assorted independently. Later, researchers discovered the third gene that also affect the kernel colour of wheat. The three independent pairs of alleles were involved in wheat kernel colour. Nilsson – Ehle found the ratio of 63 red : 1 white in F2 generation – 1 : 6 : 15 : 20 : 15 : 6 : 1 in F2 generation.

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 35.
Differentiate continuous variation with discontinuous variation.
Answer:
1. Discontinuous Variation: Within a population there are some characteristics which show a limited form of variation.
Example: Style length in Primula, plant height of garden pea. In discontinuous variation, the characteristics are controlled by one or two major genes which may have two or more allelic forms.

These variations are genetically determined by inheritance factors. Individuals produced by this variation show differences without any intermediate form between them and there is no overlapping between the two phenotypes. The phenotypic expression is unaffected by environmental conditions. This is also called as qualitative inheritance

2. Continuous Variation: This variation may be due to the combining effects of environmental and genetic factors. In a population most of the characteristics exhibit a complete gradation, from one extreme to the other without any break. Inheritance of phenotype is determined by the combined effects of many genes, (polygenes) and environmental factors. This is also known as quantitative inheritance.
Example: Human height and skin color.

Question 36.
Explain with an example how single genes affect multiple traits and alleles the phenotype of an organism.
Answer:
In Pleiotropy, the single gene affects multiple traits and alter the phenotype of the organism. The Pleiotropic gene influences a number of characters simultaneously and such genes are called pleiotropic gene. Mendel noticed pleiotropy while performing breeding experiment with peas (Pisum sativum).

Peas with purple flowers, brown seeds and dark spot on the axils of the leaves were crossed with a variety of peas having white flowers, light coloured seeds and no spot on the axils of the leaves, the three traits for flower colour, seed colour and a leaf axil spot all were inherited together as a single unit. This is due to the pattern of inheritance where the three traits were controlled by a single gene with dominant and recessive alleles. Example: sickle cell anemia.

Question 37.
Bring out the inheritance of chloroplast gene with an example.
Answer:
Chloroplast Inheritance
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 5
It is found in 4 ‘O’ Clock plant (Mirabilis jalapa). In this, there are two types of variegated leaves namely dark green leaved plants and pale green leaved plants. When the pollen of dark green leaved plant (male) is transferred to the stigma of pale green leaved plant (female) and pollen of pale green leaved plant is transferred to the stigma of dark green leaved plant, the F1 generation of both the crosses must be identical as per Mendelian inheritance. But in the reciprocal cross the F1 plant differs from each other.

In each cross, the F plant reveals the character of the plant which is used as female plant. This inheritance is not through nuclear gene. It is due to the chloroplast gene found in the ovum of the female plant which contributes the cytoplasm during fertilization since the male gamete contribute only the nucleus but not cytoplasm.

Samacheer Kalvi 12th Bio Botany Classical Genetics Additional Questions and Answers

1 – Mark Questions

Question 1.
The term ‘Genetics’ was introduced by __________
(a) Gregor Mendel
(b) Bateson
(c) Hugo de vries
(d) Carl Correns
Answer:
(b) Bateson

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 2.
Which is not a correct statements?
(A) Variations are the raw materials for evolution
(B) Variations provide genetic material for natural selection
(C) It helps the individual to adapt to changing environment
(D) Variations allow breeders to improve the crop field
(a) A and D
(b) B only
(c) C and D
(d) nono of he above
Answer:
(d) nono of he above

Question 3.
The process of removal of anthers from the flower is called __________
Answer:
Emasculation

Question 4.
An allede is __________
(a) another word for a gene
(b) alternate forms of a gene
(c) morphological expression of a gene
(d) genitic
Answer:
(b) alternate forms of a gene

Question 5.
Gregor Mendel __________
(i) was born in Czechoslovakia
(ii) did his experiments in Pisum fulvum
(iii) was the first systemic researcher in genetics
(iv) Published his results in the paper “Experiments on Plant Hybrids”
(a) All are correct
(b) (ii),(iii), (iv) are correct
(c) (i), (iii),(iv) are correct
(d) (i), (iii),(iv) are correct
Answer:
(c) (i), (iii),(iv) are correct

Question 6.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 6
Answer:
A – (ii) B – (iv) C – (iii) D – (i)

Question 7.
How many characters studied by Mendel in pisum sativum
(a) Three
(b) Five
(c) Seven
(d) Nine
Answer:
(c) Seven

Question 8.
Mendel’s work were rediscovered by __________
(a) Hugo de Vries
(b) Tschermak
(c) Carl Correns
(d) All the above
Answer:
(d) All the above

Question 9.
Crossing of F1, to any one of the parent refers to __________
(a) selling
(b) back cross
(c) test cross
(d) all of the above
Answer:
(b) back cross

Question 10.
Match the following
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 7
Answer:
A – (ii)
B – (iv)
C – (i)
D – (iii)

Question 11.
In an intergenic interaction, the gene that suppresses the pherotype of a gene is said to Crossing of F, to any one of the parent refers to __________
(a) Dominant
(b) Inhibitory
(c) Epistatic
(d) Hypostatic
Answer:
(c) Epistatic

Question 12.
Assertion (A) : Test cross is done between F2 hybrid with F1 recessive
Reason (R) : It helps to identify the homozygosity of hybrids
(a) A and R are correct R explains A
(b) A and R are incorrect
(c) A is correct R is incorrect
(d) A is incorrect R is correct
Answer:
(b) A and R are incorrect

Question 13.
Assertion (A) : Codominance is an example for intragenic interaction
Reason (R) : Interaction take place between the alleles of same gene
(a) A and R are correct R explains A
(b) A and R are incorrect
(c) A is correct R is incorrect
(d) A is incorrect R is correct
Answer:
(a) A and R are correct R explains A

Question 14.
Assertion (A) : Pleiotropic gene affects multiple traits
Reason (R) : ABO blood group is an example for Pleiotropism
(a) A and R are correct R explains A
(b) A and R are incorrect
(c) A is correct R is incorrect
(d) A is incorrect R is correct
Answer:
(c) A is correct R is incorrect

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 15.
Assertion (A) : Cytoplasmic male sterility is a Mendelian inheritance
Reason (R) : The genes for cytoplasmic male sterility in peal maize is located at mitochondrial DNA
(a) A and R are correct R explains A
(b) A and R are incorrect
(c) A is correct R is incorrect
(d) A is incorrect R is correct
Answer:
(d) A is incorrect R is correct

Question 16.
What is the phenotypic ratio in case of incomplete dominance
(a) 9 : 7
(b) 3 : 1
(c) 1 : 2 : 1
(d) 1 : 1 : 1 : 1
Answer:
(c) 1 : 2 : 1

Question 17.
Identify the mismatched pair
(a) Chloroplast inheritance – Gregor Mendel
(b) Polygenic inheritance – H. Nilsson
(c) Lethal genes – E. Baur
(d) Incomplete dominance – Carl Correns
Answer:
(a) Chloroplast inheritance – Gregor Mendel

Question 18.
Statement 1 : Intergenic gene interaction occurs between alleles at same locus
Statement 2 : Co-dominance is an example for intergenic gene interaction
(a) Statement 1 is correct & Statement 2 is incorrect
(b) Statement 1 is incorrect & Statement 2 is correct
(c) Both Statements 1 & 2 are correct
(d) Both Statements 1 & 2 are incorrect
Answer:
(c) Both Statements 1 & 2 are correct

Question 19.
Statement 1 : Test cross is done between F1 individual with homozygous recessive
Statement 2 : If F1 individual is homozygous, the rate of a monohybrid cross will be 1:1
(a) Statement 1 is correct & Statement 2 is incorrect
(b) Statement 1 is incorrect & Statement 2 is correct
(c) Both Statements 1 & 2 are correct
(d) Both Statements 1 & 2 are incorrect
Answer:
(a) Statement 1 is correct & Statement 2 is incorrect

Question 20.
Identify the incorrect statement
Answer:
(a) In incomplete dominance, the traits are blended not the genes
(b) Incomplete dominance is noticed in Mirabilis jalapa by Carl Correns
(c) It is a type of Intragenic gene interaction
(d) Incomplete dominance F2 ratio is 1 : 3 : 1
Answer:
(d) Incomplete dominance F1 ratio is 1 : 3 :1

Question 21.
In case of co-dominance, monohybrid F1 __________ is 1 : 2 : 1
(a) Genotype ratio
(b) Phenotype ratio
(c) Both genotype & Phenotype ratio
(d) Ratio is wrong
Answer:
(c) Both genotype & Phenotype ratio

Question 22.
Identify the wrong statement (s)
(i) Monohybrid cross involve the inhertance of teo alleles of a gene
(ii) The dwarf traits reappeared in F2
(iii) Law of dominance was proved by monohybrid cross
(iv) F1 monohybrid was an hererozygous
(a) i and ii
(b) iii and iv
(c) i only
(d) none of the above
Answer:
(d) none of the above

Question 23.
Result of incomplete dominance is __________
(а) Intermediate genotype
(b) Intermediate phenotype
(c) Recessive phenotype
(d) Epistasis
Answer:
(b) Intermediate phenotype

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 24.
Heterozygous Tall mono hybrid is cross with homozygous dwarf. What will be characteristic of offspring?
(a) 25 % recessive 75% dominant
(b) 75 % recessive 25% dominant
(c) 50 % recessive 50% dominant
(d) All are dominance
Answer:
(c) 50 % recessive 50% dominant

Question 25.
ABO blood group is a classical example for __________
(a) Polygenic inheritance
(b) Incomplete Dominance
(c) Epistasis
(d) Dominance
Answer:
(d) Dominance

Question 26.
RR (Red) flower of Mirabilis is crossed with White (WW) flowers. Resultant offspring are pink RW. This is an example of __________
(a) Epistasis
(b) Co-dominance
(c) Incomplete dominance
(d) Pleiotropism
Answer:
(c) Incomplete dominance

Question 27.
How many genetically different gametes are produced by a plant have genotype TtYyRr?
(a) 2
(b) 4
(c) 6
(d) 8
Answer:
(d) 8

Question 28.
When a single gene influences multiple traits then the phenomenon is called __________
(a) Pleiotropy
(b) Polygenic inheritance
(c) Epistasis
(d) Atavism
Answer:
(a) Pleiotropy

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 29.
According to Mendel which character shown dominance.
(a) Yellow flower color
(b) Yellow cotyledon color
(c) Wrinkled seeds
(d) Inflated pod
Answer:
(d) Inflated pod

Question 30.
Ratio of recessive epistasis is __________
(a) 12 : 3 : 1
(b) 9 : 7
(c) 9 : 3 : 4
(d) 9 : 6 : 1
Answer:
(c) 9 : 3 : 4

Question 31.
According to Mendel, which is not a dominant trait?
(a) Wrinkled seeds
(b) Purple flower
(c) Inflated pod form
(d) Axial flower portion
Answer:
(a) Wrinkled seeds

Question 32.
Identify the allelic interaction.
(a) Domination epistasis
(b) Co – dominance
(c) Recessive epistasis
(d) Duplicate genes
Answer:
(b) Co – dominance

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 33.
Gametes are never hybrid’ is concluded by __________
(a) Law of dominance
(b) Law of segregation
(c) Law of independent environment
(d) Law of lethality
Answer:
(b) Law of segregation

Question 34.
Factor hypothesis was proposed by __________
(a) Reginald Punnett
(b) W. Bateson
(c) Gregor Mende
(d) Carl Correns
Answer:
(b) W. Bateson

Question 35.
The 1:2:1 ratio of co-dominance process Mendel’s __________
(a) Law of dominance
(b) Law of recessiveness
(c) Law of segregation
(d) Law of independent assortment
Answer:
(b) Law of recessiveness

Question 36.
Match the following:
Epistatic interaction Example
(A) Complementary genes (i) Seed capsule in xxxxx
(B) Supplementary genes (ii) Leaf color in rice plant
(C) Inhibitory genes (iii) Grain color in maize
(D) Duplicate genes (iv) Flower color in sweet peas
Answer:
A – (iv)
B – (iii)
C – (ii)
D – (i)

2 – Mark Questions

Question 1.
Who coined the term genetics? Also define it.
Answer:
“Genetics” is the branch of biological science which deals with the mechanism of transmission of characters from parents to off springs. The term Genetics was introduced by W. Bateson in 1906.

Question 2.
Name the four major subdisciplines of genetics.
Answer:
(a) Classical genetics
(b) Molecular genetics
(c) Population genetics
(d) Quantitative genetics

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 3.
Define Heredity and variations.
Answer:
Heredity : Heredity is the transmission of characters from parents to off springs.
Variations : The organisms belonging to the same natural population or species that shows a difference in the characteristics is called variation.

Question 4.
Mendel’s theory is a particulate theory – justify.
Answer:
Mendel’s theory of inheritance, known as the Particulate theory, establishes the existence of minute particles or hereditary units or factors, which are now called as genes.

Question 5.
Which organism was studied by Gregor Mendel? How many traits does he considered on his experiments?
Answer:
Gregor Mendel selected seven pairs of characters in Pisum sativum (garden pea)

Question 6.
Name any four characters of pisum sativum that was studied by Mendel.
Answer:
Seed shape, flower color, flower position & pod color.

Question 7.
Define the terms

  1. Emasculation
  2. Alleles.

Answer:

  1. Emasculation : Removal of anthers from the flower
  2. Alleles : Alternate forms of a gene

Question 8.
Name the first and second law of Mendel.
Answer:

  1. The Law of Dominance
  2. The Law of Segregation

Question 9.
What is genotype & phenotype?
Answer:
genotype & phenotype

  1. The term genotype is the genetic constitution of an individual.
  2. The term phenotype refers to the observable characteristic of an organism.

Question 10.
Write the phenotypic and genotypic ratio of monohybrid cross.
Answer:
(a) Phenotypic ratio = 3:1.
(b) Genotypic ratio =1 : 2 : 1

Question 11.
What is test cross? Why it is done?
Answer:

  1. Test cross is crossing an individual of unknown genotype with a homozygous recessive.
  2. Test cross is used to identify whether an individual is homozygous or heterozygous for dominant character.

Question 12.
State the law of independent assortment.
Answer:
When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent to the other pair of characters. Genes that are located in different chromosomes assort independently during meiosis.

Question 13.
Give the phenotypic ratio of
(a) Dihybrid cross
(b) Dihybrid test cross
Answer:
(a) Dihybrid cross ratio = 9 : 3 : 3 : 1
(b) Dihybrid test cross ratio = 1 : 1 : 1 : 1

Question 14.
RrYyf (F1 hybrid)  rryy (recessive parent). Name the type of cross. Mention its ratio.
Answer:
Dihybrid test cross and the ratio is 1 : 1 : 1 : 1

Question 15.
How many types of gametes are produced by a dihybrid plant. If the same plant is self fertilized, how many second generation offsprings are developed?
Answer:
Four different gametes are produced by a dihybrid plant and on selfing, it yield 16 off springs.

Question 16.
Write the phenotypic ratio of trihybrid cross.
Answer:
27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

Question 17.
Define gene interaction.
Answer:
A single phenotype is controlled by more than one set of genes, each of which has two or more alleles. This phenomenon is called Gene Interaction.

Question 18.
Classify gene interactions with an example.
The gene interactions may be
(a) Intragenic gene interaction. E.g.: Codominance
(b) Intergenic gene interaction. E.g.: Epistasis

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 19.
Provide any four intergenic gene interactions.
Answer:
(a) Incomplete dominance
(b) Codominance
(c) Multiple alleles
(d) Pleiotropic genes are common examples for intragenic interaction.

Question 20.
Define intragenic interaction
Answer:
Interactions take place between the alleles of the same gene i.e., alleles at the same locus is called intragenic or intralocus gene interaction.

Question 21.
In which plant does the incomplete dominance was studied by Carl Correns? Write the ratio of the cross.
Answer:
Mirabilis Jalapa (4 o’ clock plant). Incomplete dominance ratio is 1 : 2 : 1

Question 22.
What are lethal alleles? Give example.
Answer:
An allele which has the potential to cause the death of an organism is called a Lethal Allele.
E.g : Recessive lethality in Antirrhinum species.

Question 23.
Give the proper terminologies for the following statement
(a) Single gene affecting multiple traits
(b) Single trait affected by many genes.
Answer:
(a) Pleiotropism
(b) Poly genic inheritance

Question 24.
What is intergenic gene interactions? Give example
Answer:
Interlocus interactions take place between the alleles at different loci i.e. between alleles of different genes.
Eg: Dominant Epistasis

Question 25.
Name any two extranuclear inheritance.
Answer:
(a) Chloroplast inheritance
(b) Mitrochondrial inheritance

Question 26.
What are plasmogenes?
Answer:
Plasmogenes are independent, self-replicating, extra-chromosomal units located in cytoplasmic organelles, chloroplast and mitochondrion

Question 27.
What are extra nuclear inheritance?
Answer:
Certain characters/traits are governed and inherited by genes located in cytoplasmic organelles (chloroplast or mitochondrion) other than nucleus. This is called extra nuclear inheritance.

Question 28.
Why extranuclear inheritance is called as cytoplasmic inheritance.
Answer:
Extra nuclear inheritance is due to genes located on the cytoplasmic organelles such as chloroplast and mitochondrion hence it is called cytoplasmic inheritance.

Question 29.
What is cytoplasmic male sterility?
Answer:
In Sorghum vulgare (Pearl maize), the gene located for the sterility pollens are located in the mitochondrial DNA. This phenomenon is called as cytoplasmic male sterility.

3 – Mark Questions

Question 30.
Point out any three importance of variations.
Answer:

  1. They help the individuals to adapt themselves to the changing environment.
  2. Variations allow breeders to improve better yield, quicker growth, increased resistance and lesser input.
  3. They constitute the raw materials for evolution.

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 31.
Why Mendel selected pea plants for his experiments.
Answer:
He choose pea plant because,

  1. It is an annual plant and has clear contrasting characters that are controlled by a single gene separately.
  2. Self-fertilization occurred under normal conditions in garden pea plants. Mendel used both self-fertilization and cross-fertilization.
  3. The flowers are large hence emasculation and pollination are very easy for hybridization.

Question 32.
State the law of segregation.
Answer:
The Law of Segregation (Law of Purity of gametes): Alleles do not show any blending. During the formation of gametes, the factors or alleles of a pair separate and segregate from each other such that each gamete receives only one of the two factors. A homozygous parent produces similar gametes and a heterozygous parent produces two kinds of gametes each having one allele with equal proportion. Gametes are never hybrid.

Question 33.
How many types of gametes are produced by heterozygous dihybrid plant with a genotypeRrYy? Write them.
Answer:
Four gametes – RY, Ry, rY, ry

Question 34.
Define trihybrid cross. Mention its F2 phenotypic ratio.
Answer:
A cross between homozygous parents that differ in three gene pairs (i.e. producing trihybrids) is called trihybrid cross, F2 Phenotypic ratio -27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

Question 35.
Define co-dominance. How it is proved by using Gossypium species?
Answer:
The phenomenon in which two alleles are both expressed in the heterozygous individual is known as codominance. The codominance was demonstrated in plants with the help of electrophoresis or chromatography for protein or flavonoid substance.

Example: Gossypium hirsutum and Gossypium sturtianum, their F1 hybrid (amphiploid) was tested for seed proteins i by electrophoresis. Both the parents have different banding patterns for their seed proteins. In hybrids, additive banding pattern was noticed. Their hybrid shows the presence of both the types of proteins similar to their parents.

Question 36.
Give an account on cytoplasmic male sterility.
Answer:
Male sterility found in pearl maize (Sorgum vulgare) is the best example for mitochondrial cytoplasmic inheritance. So it is called cytoplasmic male sterility. In this, male sterility is inherited maternally. The gene for cytoplasmic male sterility is found in the mitochondrial DNA.

Question 37.
Write a short note on Atavism.
Answer:
Atavism is a modification of a biological structure whereby an ancestral trait reappears after having been lost through evolutionary changes in the previous generations. Evolutionary traits that have disappeared phenotypically do not necessarily disappear from an organism’s DNA. The gene sequence often remains, but is inactive.

Such an unused gene may remain in the genome for many generations. As long as the gene remains intact, a fault in the genetic control suppressing the gene can lead to the reappearance of that character again. Reemergence of sexual reproduction in the flowering plant Hieracium pilosella is the best example for Atavism in plants.

5 – Mark Questions

Question 38.
Explain Dihybrid cross in pea plant.
Answer:
The crossing of two plants differing in two pairs of contrasting traits is called dihybrid cross. In dihybrid cross, two characters (colour and shape) are considered at a time. Mendel considered the seed shape (round and wrinkled) and cotyledon colour (yellow & green) as the two characters. In seed shape round (R) is dominant over wrinkled (r); in cotyledon colour yellow (Y) is dominant over green (y).

Hence the pure breeding round yellow parent is represented by the genotype RRYY and the pure breeding green wrinkled parent is represented by the genotype rryy. During gamete formation the paired genes of a character assort out ‘ independently of the other pair. During the F1 x F, fertilization each zygote with an equal probability receives one of the four combinations from each parent. The resultant gametes thus will be genetically different and they are of the following four types:
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 8

(1) Yellow round (YR) – 9/16
(2) Yellow wrinkled (Yr) – 3/16
(3) Green round (yR) – 3/16
(4) Green wrinkled (yr) -1/16

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 9

These four types of gametes of F1 dihybrids unite randomly in the process of fertilization and produce sixteen types of individuals in F2 in the ratio of 9:3:3:1 as shown in the figure. Mendel’s 9:3:3:1 dihybrid ratio is an ideal ratio based on the probability including segregation, independent assortment and random fertilization. In sexually reproducing organism / plants from the garden peas to human beings, Mendel’s findings laid the foundation for understanding inheritance and revolutionized the field of biology. The dihybrid cross and its result led Mendel to propose a second set of generalisations that we called Mendel’s Law of independent assortment.

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 39.
How does the wrinkled gene make Mendel’s peas wrinkled? Find out the molecular explanation.
Answer:
The protein called starch branching enzyme (SBEI) is encoded by the wild-type allele of the gene (RR) which is dominant. When the seed matures, this enzyme SBEI catalyzes the formation of highly branched starch molecules. Normal gene (R) has become interrupted by the insertion of extra piece of DNA (0.8 kb) into the gene, resulting in allele. In the homozygous mutant form of the gene (R) which is recessive, the activity of the enzyme SBEI is lost resulting in wrinkled peas.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics
The wrinkled seed accumulates more sucrose and high water content. Hence Ore osmotic pressure inside the seed rises. As a result, the seed absorbs more water and when it matures it loses water as it dries. So it becomes wrinkled at maturation. When the seed has at least one copy of normal dominant gene heterozygous, the dominant allele helps to synthesize starch, amylopectin an insoluble carbohydrate, with the osmotic balance which minimises the loss of water resulting in smooth structured round seed.

Question 40.
Describe incomplete dominance exhibited by Mirabilis jalapa.
Answer:
The German Botanist Carl Correns’s (1905) Experiment – In 4 O’ clock plant, Mirabilis jalapa when the pure breeding homozygous red (R1R1) parent is crossed with homozygous white (R2R2), the phenotype of the F1 hybrid is heterozygous pink (R1R2). The F1 heterozygous phenotype differs from both the parental homozygous phenotype. This cross did not exhibit the character of the dominant parent but an intermediate colour pink. When one allele is not completely dominant to another allele it shows incomplete dominance. Such allelic interaction is known as incomplete dominance. F1 generation produces intermediate phenotype pink coloured flower.
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics
When pink coloured plants of F1 generation were interbred in F2 both phenotypic and genotypic ratios were found to be identical as 1 : 2 :1(1 red: 2 pink: 1 white). Genotypic ratio is 1 R1 R1 : 2 R1R2 : 1 R2R2. From this we conclude that the alleles themselves remain discrete and unaltered proving the Mendel’s Law of Segregation. The phenotypic and genotypic ratios are the same. There is no blending of genes. In the F1 generation R1 and R2 genes segregate and recombine to produce red, pink and white in the ratio of 1 : 2 : 1. R1 allele codes for an enzyme responsible for the formation of red pigment. R2 allele codes for defective enzyme.

R1 and R2 genotypes produce only enough red pigments to make the flower pink. Two R1 R2 are needed for producing red flowers. Two R2R2 genes are needed for white flowers. If blending had taken place, the original pure traits would not have appeared and all F2 plants would have pink flowers. It is very clear that Mendel’s particulate inheritance takes place in this cross which is confirmed by the reappearance of original phenotype in F2.

Higher Order Thinking Skills (HOTs) Questions

Question 1.
A yellow colour flower plant indicated by YY is crossed with white color flower plant denoted by yy.
(a) following the Mendelian inheritance pattern, what would be the flower color is first filial generation?
(b) Which Mendelian principle is illustrated in this cross?
(c) Derive the cross and state the phenotypic ratio of yellow flowers to white flowers in F2 generation?
Answer:
(a) F1 plants produce yellow colour flower plants.
(b) Law of dominance and Law of segregation
(c) Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 12

Question 2.
Mala is a genetic research student. She was given a plant to identify whether it is a homozygous or heterozygous for a particular trait. How will she proceed further?
Answer:
To identify the plant genotype whether homozygous or heterozygous Mala can perform test cross, where the individual is crossed with homozygous recessive for the trait. If the plant is heterozygous then the resultant progenies would be in the ratio 50:50

Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics

Question 3.
In the chart given below, ‘AA’ are the genes located in a chromosome of Pisum sativum.
Answer:
Samacheer Kalvi 12th Bio Botany Solutions Chapter 2 Classical Genetics 13
Observe the chart and mention the genetic phenomenon does it indicates.
Pleitrophy – A single gene affecting many traits. Here the single gene AA controls the traits – for flower colour, seed colour and leaf axil spot.

Question 4.
Give the F2 phenotypic ratio of
(a) Supplementary genes
(b) Complementary genes
(c) Dominant epistasis
Answer:
(a) Supplementary genes – 9 : 3 : 4
(b) Complementary genes – 9 : 7
(c) Dominant epistasis -12 : 3 : 1

Question 5.
Name the respective pattern of inheritance where F1 phenotype
(a) resembles any one of the two parents
(b) is an intermediate between two parental traits.
Answer:
(a) Dominance
(b) Incomplete dominance

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