Frank ICSE Class 10 Biology Solutions Chapter 3 Principles of Genetics

ICSE Solutions for Class 10

Question 1: Who was the ‘Father of Genetics’?
Solution 1:
The Father of Genetics “Gregor Johann Mendel”.

Question 2: What is Genetics?
Solution 2:
Subject that deals with the inheritance and Variation. The transfer of similar character from parents to their offspring.

Question 3: What is heredity?
Solution 3:
The term heredity is defined as transmission of genetic characters from parents to offspring.

Question 4: In which cross is 3:1 ratio obtained?
Solution 4:
3:1 ratio obtained in Monohybrid cross.

Question 5: What is the dihybrid cross ratio?
Solution 5:
The Dihybrid cross ratio is 9:3:3:1.

Question 6: Which seven characters did Mendel use for his experiments?
Solution 6:

1. Stem LengthTall or Dwarf
2. Flower PositionAxial or Terminal
3. Flower ColourRed or Yellow
4. Pod ColourGreen or Yellow
5. Pod ShapeInflated or Constricted
6. Seed ShapeRound or Wrinkled
7. Cotyledon ColourYellow or White

Question 7: Define the following:
(i) Genotype
(ii) Phenotype
(iii) Homozygous
(iv) Heterozygous
(v) Allele
(vi) Dominant
(vii) Recessive
Solution 7:
Genotype – Representation of genetic complement of an individual with respect to one or more character.
Phenotype – It is observable morphological apperance.
Homozygous – Two alleles of a gene are identical.
Heterozygous – An individual having two different alleles.
Allele – Genes which code for a pair of contrasting traits are known as alleles.
Dominant – Factors that expresses itself is called dominant.
Recessive – Factors that fail to express is termed as recessive

Question 8: Who was Mendel?
Solution 8:
Gregor Johann Mendel was the first to demonstrate the scientific basis of inheritance and variation by conducting hybridisation experiment. He is called the ‘Father of Genetics’.

Question 9: Name Mendel’s laws.
Solution 9:
Mendel’s laws are:
Law of Dominance
Law of Segregation
Law of Independent Assortment

Question 10: What do you understand by monohybrid cross?
Solution 10:
Monohybrid cross is a cross between one pair of contrasting trait of a character or alleles.

Question 11: Explain dihybrid cross.
Solution 11:
Mendal also crossed pea plants differing in two characters (dihybrid cross) to verify the results of monohybrid crosses. This helped him to understand inheritance of two pairs of factors at a time.
A cross was made between a pure round yellow seeded pea plant (RRYY) with wrinkled green-seeded pea plant (rryy). Yellow colour is dominant over green and round seed shape over wrinkled seed shape.
The hybrids – YyRr produced four types of seeds in F2 generation:
(i) Yellow cotyledons and round seeds (YYRR)
(ii) Yellow cotyledons and wrinkled seeds (YYrr)
(iii) Green cotyledons and round seeds (yyRR)
(iv) Green cotyledons and wrinkled seeds (yyrr)
Phenotypic ratio of a dihybrid cross is 9:3:3:1.

Frank ICSE Class 10 Biology Solutions Chapter 3  Principles of Genetics

Question 12: What do you infer from the law of segregation?
Solution 12:
The law is based on the fact that the two factors of a character present in an individual do not get mixed up. During gamet or spore formation factors of a pair separate or segregate from each other so that a gamet carries only one factor of a character

Question 13: Why is the law of segregation called law of purity of gametes?
Solution 13:
According to this law when F1 is selfed then in F2 generation all the characters or traits are segregated that is why it is called the law of segregation. At the time of gametogenesis from F1 parents each gamet contain only one allele of the gene that mean each gamet is pure that is why it is called the law of purity of gametes

Question 14: Elucidate “Law of independent Assortment”. Explain how Mendel achieved it.
Solution 14:
Thak Law states that when two pairs of opposing characters in a hybrid the distribution of one pair of traits is independent to the other pair of the trait.
Based on dihybrid ratio of 9:3:3:1 in F2 generation, Mendel discovered that when a plant with two dominant alleles was crossed with another with the matching recessive alleles in the F2 generation
These were novel recombinations that have never been seen before in either the parent or F1 generations.

Question 15: How are Mendel’s laws important?
Solution 15:
Below are the Importance of Mendel’s Laws:
1. It is simple to create a hybrid with the necessary characteristics.
2. Two characters that is dominant and recessive can be found.
3. Improved crosses.
4. In needed pure recessive traits can be used
5. Even before a cross is made, the genotypes and phenotypes of the next generation can be predicted.

Question 16: Give three exceptions to Mendel’s laws.
Solution 16:
Exceptions to Mendel’s Laws are-
Incomplete Dominance–F1 phenotype does not resemble either of the two parents and is in the between the two
Linkage–physical assessment of the two genes on similar chromosome
Multiple Allelism- presence of more than two allel for the same character

Question 17: On which plant Mendel performed his experiments?
Solution 17:
Pea plant or Pisum sativum.

Question 18: What determines the sex of a child in humans?
Solution 18:
In humans, sex chromosomes determine a child’s gender

Question 19: Predict the genotype and phenotype of the following crosses in pear.
(i) TT×Tt
(ii) tt×TT
(iii) TTrr×ttRR
(iv) TtRr×TtRr
(Capital letters show dominance)
(i) Give the ratio of phenotypes of these crosses.
(ii) Mention whether the cross is a monohybrid or dihybrid.
Solution 19:

Frank ICSE Class 10 Biology Solutions Chapter 3  Principles of Genetics
Frank ICSE Class 10 Biology Solutions Chapter 3  Principles of Genetics

(i) Phenotypic ratio of:
(a) TT× Tt – All progeny plants will be tall.
(b) tt × TT – All the progeny plants will be tall.
(c) TTrr × ttRR – All progeny will be tall having round seeds.
(d) TtRr × TtRr – 9:3:3:1
(9-Tall and Round seeds, 3-Tall and wrinkled seeds, 3-Dwarf and round seeds, 1- Dwarf and Wrinkled seeds)
(ii) a. monohybrid
b. Monohybrid
c. Dihybrid
d. Dihybrid

Question 20: Note down the allele pairs studied by Mendel. Mention which allele is dominant.
Solution 20:

 Allele pairsDominant
1.Stem of length – Tall or DwarfTall
2.Shape of seed – Round or WrinkledRound
3.Cotyledon Colour – Yellow or greenYellow
4.Shape of pod – Inflated or ConstrictedInflated
5.Colour of pod – Green or YellowGreen
6.Position of Flowers – Axial or TerminalAxial
7.Flower Colour – Red or whiteRed

Question 21: How did Mendel’s work come to light?
Solution 21:
Mendel’s work was unnoticed till 1900, then three scientist
Hugo de vrise
Carl correns
Erich von Tschermak
Working seperately brought and rediscovered mendel’s experiment to lime light.

Question 22: Define the following:
(i) Autosomes
(ii) Sex chromosomes
(iii) Sex-linked characters
Solution 22:
Autosomes–chromosomes other than sex chromosomes are present in the body are called autosomes
Sexchromosomes–chromosomes that determine the gender of an individual are called sex chromosome.
Sex-linked characters–Sex related characters are characters or traits that are controlled by genes found on the sex chromosome.

Question 23: How is sex of zygote determined in humans?
Solution 23:
Human beings have 22 pairs of autosomes and one pair of sex chromosomes all the ova formed by female are similar in their chromosome type (22+X) therefore female are homogametic male individual produce two types of sperm during the process of spermatogenesis 50% of the total sperm produce is the X chromosome and rest 50% has Y chromosome beside the autosomes. there is an eQuestion ual probability of fertilization of the oven with the sperm carrying either X aur y chromosome if ovum fertilises (22+X) with type sperm The zygote develops into a female (44+XX) and the fertilization of ovum with(22+Y) type sperm result into the male individual (44+XY). this, genetic makeup of a sperm determine the sex of a child. IT is also clear that in each pregnancy there is a always 50% or half probability of either a male or female child.

Question 24: What do you understand by sex-linked inheritance?
Solution 24:
Sex related characters are characters or traits that are controlled by genes found on the sex chromosome

Question 25: What do you know about haemophilia?
Solution 25:
It is X linked recessive trait therefore shows its transmission from normal carrier female to male progeny. Due to presence of defective form of blood clotting factor exposed blood of effective individual fail to coagulate.

Question 26: What is colour blindness?
Solution 26:
Colour blindness is a recessive sex linked trait in which the eye fails to distinguish between Red and green colours.

Question 27: What is the cause of haemophilia and colour blindness?
Solution 27:
Cause of Haemophilia –Haemophiliaisan X-linked inherited disease. A female must have homozygosity for the recessive haemophilia gene, whereas a male with a single affected X chromosome is a haemophiliavictim.
Cause of Colour Blindness–Colour blindness is the effect of arecessivegene.
Because. both X chromosomes must carry the same recessive gene in females, but males only have one X chromosome, a single damaged chromosome produces colorblindness.

Question 28: Why do you think that more males are affected by sex-linked diseases?
Solution 28:
The sex linked diseases occurs due to recessive gene on X chromosomes and the males have a single X chromosomes that’s why males are more affected by sex linked diseases.

Question 29: Why can’t a man transfer a sex linked disease directly to his son?
Solution 29:
A man can never transfer a sex linked gene directly to his son because the father has sex linked disease present on the X chromosome and son inherits only the Y chromosomes from his father.

Question 30: A woman has normal vision but her father was colour blind. If she is married to a colour blind person, report on the occurrence of the disease in the progeny.
Solution 30:
One son and one daughter as colorblind and one daughter as a career and the Son will be normal this is the progeny of a normal woman and the heamophilic man.

Question 31: What is the other name of Bleeder’s disease?
Solution 31:
The other name of bleeder’s diseases is Haemophilia

Question 32: What is sex-linked inheritance?
Solution 32:
Sex related characters are characters or traits that are controlled by genes found on the sex chromosome.

Question 33: (i) State Mendel’s law of dominance.
(ii) Suppose you are given two pairs of contrasting characters:
Seed colour →yellow and green
Seed coat→ round and wrinkled
Fill in the following table to show that F2 generation according to the principle of independent assortment as given by Mendel

Selfing among hybrids of F1RYRyrYRy
F2 generation    

Solution 33:
Mendel law of dominance., This law is used explain the expression of only one of the parental trait in a monohybrid cross in the F1 and the expression of both in the F2. It also explains the proportion of 3:1 obtained in F2 generation. This law is not universally applicable


Selfing among hybrids of F1RYRyrYRy
F2 generation9 Round and yellow seeds3 Round and green seeds3 Wrinkled and yellow seeds1 Wrinkled and green seeds.

Question 34: Answer the following briefly:
(i) Explain with the help of a chart what will be the colour of a child’s hair if father has got dominant gene for black hair and mother has recessive gene for brown hair?
(ii) Explain the following terms:
    (a) Laws of Inheritance.
    (b) Identical twins.
(iii) Define the term heredity.

Solution 34:

Frank ICSE Class 10 Biology Solutions Chapter 3  Principles of Genetics


(a) Inheritance Law: Mendel experimented with several garden pea varieties before formulating a few laws to examine the inheritance of traits in living organisms.
(b) Identical twins: After conception, a single fertilised egg or zygote separates into two halves, resulting in the creation of two separate embryos that later mature into identical twins.
(iii) Heredity can be defined as the transmission of genetically determined features from one generation to the next.

Question 35: A family consists of two parents and their five children and the pedigree chart below show the inheritance of the trait colour blindness.

Frank ICSE Class 10 Biology Solutions Chapter 3  Principles of Genetics

i) Who is colour blind in parents- Father or Mother?
(ii) How many daughters and sons have been born in the family?
(iii) What does the child 1 indicate about this trait?
(iv) Complete the depiction of all probabilities of the trait among the children 2-5 in the chart.
(v) On which chromosoms is the gene of this trait located?
(vi) Name one other trait in humans which follows the similar inheritance.
Solution 35:
(i) Father is colorblind
(ii) 3 daughters and two sons.
(iii) Child 1 is colorblind.
(iv) All daughters from 2-5 are carriers while all the sons are normal.
(v) Xchromosome.
(vi) Haemophilia.

Q36. Choose the correct answer:

(i) Mendel conducted his hybridization experiments on
(a) potato
(b) garden pea
(c) cow pea
(d) pigeon pea


garden pea

(ii) If a homozygous tall plant is crossed with a heterozygous tall plant, the proportion of tall progeny would be
(a) 25%
(b) 50%
(c) 75%
(d) 100%



(iii) Mendel used ______ pairs of a characters for his experiments.
(a) 5
(b) 6
(c) 7
(d) 4



(iv) Father of genetics
(a) Darwin
(b) Pasteur
(c) Lamarck
(d) Mendel



(v) The allele which masks the effect of its complement is
(a) dominant
(b) recessive
(c) monohybrid
(d) dihybrid



(vi) If any of Mendel’s characters were linked; one would have been unable to derive.
(a) Law of Dominance
(b) Law of Segregation
(c) Law of Independent Assortment
(d) None of these


Law of Independent Assortment

(vii) The contrasting characters used by Mendel are called
(a) alleles
(b) heteromorphs
(c) genes
(d) none of the above



(viii) If a pea plant with round seeds is selfed and the offspring are in the ratio 3:1, then the plant is
(a) homozygous
(b) heterozygous
(c) both
(d) none of these



(ix) A cross where two pairs of alleles are considered is a
(a) dihybrid cross
(b) monohybrid cross
(c) polyhybrid cross
(d) test cross


dihybrid cross

(x) Mendel was born in
(a) Czechoslovakia
(b) Austria
(c) England
(d) Portugal



(xi) Human sex chromosomes are
(a) X and O
(b) Y and O
(c) X and Y
(d) none of these


X and Y

(xii) Haemophilia is due to recessive gene on
(a) X chromosome
(b) Y chromosome
(c) autosome
(d) none of these


X chromosome

(xiii) Chromosomes identical in male and female are called
(a) sex chromosomes
(b) autosomes
(c) heterosomes
(d) dominant



(xiv) Males have more chances of suffering from sex-linked disease because of
(a) one Y chromosome
(b) one X chromosome
(c) autosomes
(d) none of these


one X chromosome

(xv) A single recessive trait, able to express must be on
(a) Y chromosome
(b) X chromosomes in male
(c) X chromosome in female
(d) autosome


X chromosomes in male

(xvi) A carrier haemophilic woman marries a haemophilic man. What are the chances for her progeny to be haemophilic?
(a) 25%
(b) 75%
(c) 50%
(d) 100%



(xvii) A colour blind woman marries a normal man, in the progeny
(a) one son and one daughter are normal
(b) sons are colour blind and daughters are normal
(c) sons are colour blind and daughters are carriers
(d) none of these


sons are colour blind and daughters are carriers

(xviii) A man can transfer his sex-linked gene to his
(a) son
(b) daughter
(c) both
(d) none of these



Frank ICSE Class 10 Biology Solutions Chapter 3 Principles of Genetics