Genetics Questions and Answers ICSE Class 10

Question 1 : Name the type of gene, which in the presence of a contrasting allele is not expressed.

Answer : Recessive gene is not expressed in the presence of a contrasting dominant allele.

Question 2 : Explain the term monohybrid cross.

Answer : It is a type of cross which is performed by taking only one pair of contrasting character or one feature at a time.

Question 3 : State Mendel’s law of segregation.

Answer : During gamete formation, the alleles for each gene seggregate from each other so that each gamete carries only one allele for each gene.

Question 4 : After mitotic cell division, a female human cell will have

a) 44 + XX-chromosome

b) 44 + XY-chromosome

b) 22 + X-chromosome

c) 33 + Y-chromosome

Answer : a) 44 + XX-chromosome.

Question 5 : Give the technical term for the sudden heritable change in the gene.

Answer : Mutation is the term used for a sudden heritable change in the gene.

Question 6 : Name the physical expression of genes in an individual.

Answer : Phenotype is the physical expression of genes in an individual.

Question 7 : The recessive gene is one of that expresses itself in

a) heterozygous condition

b) homozygous condition

c) F2-generation

d) Y-linked inheritance

Answer : b) Homozygous condition.

Question 8 : Briefly explain the term gene.

Answer : Gene is a portion (or sequence) of DNA that codes for a known cellular function or process. These are also called the unit of inheritance containing the information required to express a trait.

Question 9 : Briefly explain the term allele.

Answer : Allele is one of a number of alternative form of the same gene.

Question 10 : Given below is set with four terms. In the set, a term is an odd one that cannot be grouped in the same category to which the other three belong. Identify the odd one in the set and name the category to which the remaining three belong.

Haemophilia, colour blindness, albinism, night blindness.

Answer : The difference between set, odd one and category are given below.

Set	Odd one	Category
Haemophilia, colour blindness, albinism, night blindness	Night blindness (it is caused due to nutritional deficiency)	Sex-linked diseases

Question 11 : Give the biological term for the suppressed allele of a gene.

Answer : Suppressed allele of a gene pair is called recessive allele.

Question 12 : Rewrite and complete the following sentence by inserting the correct word in the space indicated.

Phenotype is the observable characteristic which is ………………….. controlled.

Answer : Phenotype is the observable characteristic which is generally controlled.

Question 13 : Write down the difference between the following pair as indicated within the bracket.

Monohybrid and dihybrid cross (phenotypic ratio).

Answer : Phenotypic ratio in F2-generation of monohybrid cross is 3:1.

While, phenotypic ratio in F2-generation of dihybrid cross is 9 : 3 : 3 : 1

Question 14 : State whether the following statement is true or false. If false, rewrite the correct form of the statement by changing the first or last word only.

Chromosomes other than the pair of sex-chromosomes are called alleles.

Answer : The statement is false. It can be correctly written as chromosomes other than the pair of sex-chromosomes are called autosomes.

Question 15 : Give one point of difference between the following on the basis of what is given in the bracket?

Genotype and phenotype (definition).

Answer :

Genotype	Phenotype
It is the genetic makeup of an organism.	It is the physical or observable characteristic of an organism.

Question 16 : Identify and name the term from the statement given below:

A pair of chromosomes carrying dissimilar alleles for a particular character.

Answer : A pair of chromosomes carrying dissimilar alleles of a particular character is called heterozygous.

Question 17 : Name the two sex-linked diseases in males.

Answer : Colour blindness and haemophilia are the two sex-linked diseases in males.

Question 18 : Give the dihybrid ratio. Name and state the law which explains the same.

Answer : The dihybrid ratio is 9 : 3 : 3 : 1

Based on the observation in dihybird crosses Mendel proposed Law of independent assortment (third law) which states that when two pairs of contrasting characters are combined in a hybrid, segregation of members of one pair of a gamete is independent of member of another pair of gamete.

Question 19 : Name the pair of genes responsible for a particular characteristics in an individual.

Answer : The pair of genes responsible for a particular characteristics in an individual are called alleles.

Question 20 : Distinguish between on the basis of what is given in the bracket.

Pure strains and hybrid strains (definition).

Answer : The difference between pure strains and hybrid strains are given below:

Pure strains	Hybrid strains
These are made up of some type of alleles.	These are made up of different types of alleles.

Question 21 : Name the genetic constitution of an organism.

Answer : Genotype is known as the genetic constitution of an organism.

Question 22 : State Mendel’s law of dominance.

Answer : This law states that when two alternative forms of trait or character are present in an organism, only one factor expressed itself in F1-progeny. This factor is called dominant factor, while the other factor which remains hidden is called recessive factor. It explains the expression of a gene in a cross and 3 : 1 ratio is obtained in F2-generation.

Question 23 : What is a dihybrid ratio?

Answer : The ratio of each phenotype (or appearance) of the seeds in the F2-generation obtained in a dihybrid cross is called dihybrid ratio, i.e. 9 : 3 : 3 : 1.

Question 24 : Define a phenotype.

Answer : Phenotype are the physical or observable characterisitics of an organism which are generally controlled.

Question 25 : What are autosomes?

Answer : A chromosome that is not an allosome, i.e. not sex chromosome is called an autosome. These are exactly similar chromosomes in both males and females (22 pairs).

Biology Questions and Answers ICSE Class 10 :