12th Bio - Botany - Book Back Answers - Chapter 2 - English Medium Guides

 

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Tamil Nadu Board 12th Standard Bio-Botany - Chapter 2: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Chapter 2 – Bio-Botany from the Tamil Nadu State Board 12th Standard Bio-Botany textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Bio-Botany Chapter 2 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

Unit 2 - Classical Genetics

I. Multiple Choice Questions

1. Extra nuclear inheritance is a consequence of presence of genes in
a) Mitochondria and chloroplasts
b) Endoplasmic reticulum and mitochondria
c) Ribosomes and chloroplast
d) Lysososmes and ribosomes
Answer Key:
a) Mitochondria and chloroplasts

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 Key:
d) aabb

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

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

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 x rryy?
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 and wrinkled seeds with yellow cotyledons
Answer Key:
d) Round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons

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 Key:
c) Crossing the F1 hybrid with a double recessive genotype

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 F1 generation?
a) 9:1
b) 1:3
b) 3:1
d) 50:50
Answer Key:
d) 50:50

8. Select the correct statement from the ones given below with respect to dihydrid 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 linked ones
Answer Key:
a) Tightly linked genes on the same chromosomes show very few combinations

9. 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 Key:
d) Co-dominance

10. Fruit colour in squash is an example of
a) Recessive epistatsis
b) Dominant epistasis
c) Complementary genes
d) Inhibitory genes
Answer Key:
b) Dominant epistasis

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

12. The epistatic effect, in which the dihybrid cross 9:3:3:1 between AaBb x 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 same loci
Answer Key:
b) Interaction between two alleles of different loci
c) Dominance of one allele to another alleles of same loci

13. In a test cross involving F1 dihybrid 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 same chromosome
d) Both of the characters are controlled by more than one gene
Answer Key:
d) Both of the characters are controlled by more than one gene

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

15. 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 Key:
c) Law of independent assortment

16. “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 Key:
c) Law of segregation

17. 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 Key:
a) Epistatic

18. Pure tall plants are crossed with pure dwarf plants. In the F1 generation, all plants were tall. These tall plants of F1 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 Key:
a) Dominance


19. The dominant epistatis ratio is
a) 9:3:3:1
b) 12:3:1
c) 9:3:4
d) 9:6:1
Answer Key:
b) 12:3:1

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

21. 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 Key:
b) Trichomal glandular or non-glandular

II. Short Answer Questions

1. Name the seven contrasting traits of Mendel. Character Dominant Trait Recessive Trait

1. Plant Height                         Tall            Dwarf

2. Flower position                   Axial         Terminal

3. Flower colour                      Purple       White

4. Pod form                               Inflated     Constricted

5. Pod colour                            Green       Yellow

6. Seed Shape                          Round       Wrinkled

7. Cotyledon colour                Yellow       Green

 

2. What is meant by true breeding or pure breeding lines / strain?

• Plant has undergone continuous self- pollination.
• It producing stable trait inheritance from parent to offspring is called true breeding lines.
• Pure line breed refers to homozygosity only

 

3. Give the names of the scientists who re discovered Mendelism.

• Hugo de Vries of Holland,
• Carl Correns of Germany and
• Erich von T schermak of Austria in 1900.

4. What is back cross?

• F₁ hybrid with any one of the parental genotype is called Back cross
• The back cross is of two types. 1. Dominent back cross 2. Recessive back cross.

 

5. Define Genetics.

• "Genetics" is the biological science which deals with Heridity and variation.

 

6. What are multiple alleles?

• Three or more allelic forms of a gene occupy the same locus in a given pair of homologous chromosomes, are called multiple alleles.

 

7. What are the reasons for Mendel's successes in his breeding experiment?

• He applied mathematics&statistical methods to biology
• He followed scientific methods
• He kept accurate and detailed data records of the outcome of his crosses.
• His experiments were carefully planned and he used large samples.
• The parents selected by Mendel were pure breed lines.

 

8. Explain the law of dominance in monohybrid cross.

• Monohybrid cross is the inheritance of a single character (plant height).
• The gene for plant height has two alleles: Tall (T) x Dwarf (t)
• The two alleles of a single gene 
• When the FI generation was selfed, 787 of 1064 F2 plants were tall and 277 of 1064 were dwarf in the ratio of 3:1
• The dwarf trait disappeared in the F1 generation only to reappear in the F2 generation.
• This law of Dominance gives an explanation to the monohybrid cross    
  

• The expression of only one of the parental characters in F1 generation
• The expression of both in the F2 generation.
• It also explains the proportion of 3:1 obtained at the F2
• The Law of Dominance and the Law of Segregation give suitable explanation to Mendel's monohybrid cross.

 

9. Differentiate incomplete dominance and codominance.

	Incomplete dominance	Co dominanсе
1	The phenotype of F1 hybrid does not resemble either of the parent	The phenotype of F1 hybrid resemble both the parents
2	F1 hybrid possess new phenotype	New phenotype is not produced.
3	Ex. Mirabilis jalapa	Ex. Camellia

 

10. What is meant by cytoplasmic inheritance?

• Cytoplasmic organelles such as chloroplast and mitochondrion that act as inheritance vectors, called Cytoplasmic inheritance.

 

11. Describe dominant epistasis with an example.

• The gene that suppresses or masks the phenotypic expression of a gene at another locus is known as epistatic.
• Example
• In summer squash fruit colours maybe white, yellow or green. White fruits are produced by a dominant epistatic allele W
• At another locus G for yellow fruits is dominant to its allele g for green fruits
• Dominent white hides the effects of yellow or green.
• The white fruit (WWgg) is crossed with yellow fruit (wwGG).
• The F1 plants have white fruit and are heterozygous (WwGg).
• The F1 heterozygous plants are crossed.
• They give rise to F2 with the phenotypic ratio of
• 12 white: 3 yellow: 1 green.
• W is epistatic to the alleles 'G' and 'g'

• White is dominent which masks the effect of yellow or green.
• Homozygous recessive ww genotypes only 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 (3/16).

 

12. Explain polygenic inheritance with an example.

• A group of genes that together determine a characteristic of an organism is called polygenic inheritance.
• It was first demonstrated by Swedish Geneticist H. Nilsson - Ehle (1909) in wheat kernels.
• Kernel colour is controlled by two genes each with two allcles, one with red kernel colour was dominant to white.
• He crossed the pure breeding dark red (R1R1 R2R2)and a white (r1r1r2r2).
• In the F1 generation medium red were obtained with the genotype R1r1R2r2.
• F1 selfing produces four types of gametes R1R2, R1r2, r1R2, r1r2.  

• 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.
• Three R genes: Medium - dark red.
• Two R genes. Medium-red,
• One R gene: Light red.
• Absence of R gene: White kernel colour.

 

13.Differentiate continuous variation with discontinuous variation.

	Continuous variation	Discontinuous variation.
1	It shows continuous gradation of a character in a population	It shows discontinuous range of a character in a population
2	It is a quantitative inheritance	It is a qualitative inheritance
3	Intermediate forms are present	Intermediate forms are Absent
4	Characters controlled by many genes	Characters controlled by one/two genes
5	Phenotypic expression is affected by environmental conditions	Phenotypic expression is un affected by environmental conditions
6	Overlapping between the two phenotypes	No overlapping between the two phenotypes
7	Ex. Human height & Skin colour	Ex. Style length of primula,plant height of garden pea

 

14. Explain with an example how single genes affect multiple traits and alleles the phenotype of an organism.

• A single gene affects multiple traits and after the phenotype of the organism is called Pleiotropy.
• The Pleiotropic gene influences a number of characters simultaneously Such genes are called pleiotropic gene.
• Mendel noticed in pens (Pisum sativum).
• purple flowers, brown seeds and dark spot on the axils of the leaves crossed with
• white flowers, light coloured seeds and no spot on the axils of the leaves,
• Flower colour, seed colour and a leaf axil spot all were inherited together as a single unit.
• This is due to the three traits were controlled by a single gene with dominant and recessive alleles.

 

15. Bring out the inheritance of chloroplast gene with an example.

• Cytoplasmic organelles such as chloroplast and mitochondrion that act as inheritance vectors, called Cytoplasmic inheritance.
• It is found in 4 O' Clock plant (Mirabilis jalapa).
• There are two types of variegated leaves 1. dark green leaved plants and 2. 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 he identical as per Mendelian inheritance.
• But in the reciprocal cross the F1 plant differs from cach other.
• In each cross, the F1 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

• It contributes the cytoplasm during fertilization.
• since the male gamete contribute only the nucleus but not cytoplasm.

III. Long Answer Questions

12th bio botany

IV. Exercise

12thbio botany