SELINA Solutions for Class 10 Biology Chapter 3 - Genetics - Some Basic Fundamentals

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Chapter 3 - Genetics - Some Basic Fundamentals Exercise Ex. 1

Question A.1

Which one of the following is the phenotypic monohybrid ratio in F2 generation?

a) 3 : 1

b) 1 : 2 : 1

c) 2 : 2

d) 1 : 3

Solution A.1

a) 3 : 1

Question A.2

If a pure tall plant is crossed with a pure dwarf plant, then offspring will be

(a) all tall

(b) all dwarf

(c) 3 tall 1 dwarf

(d) 50% tall 50% dwarf

Solution A.2

(a) all tall

Question A.3

The 9:3:3:1 dihybrid ratio is due to

(a) segregation

(b) crossing over

(c) independent assortment

(d) homologous pairing

Solution A.3

(c) independent assortment

Question A.4

A plant with green pods and smooth seeds with genotype Ggss will give rise to the following gametes:

(a) Gg and Ss

(b) Gs and ss

(c) Gs and gs

(d) Gg and gs

Solution A.4

(c) Gs and gs 

Question B.1

Match the terms in column I with their the explanations in column II

 

Column I

(Term)

Column II

(Explanation)

a

 Genetics

(i) Chromosomes similar in size and shape

b

Autosomes

(ii) The alternative forms of a gene

c

Recessive gene

(iii) Study of laws of inheritance of characters

d

Allele

(iv) A gene that can express when only in a similar pair

e

Homologous chromosomes

(v) Chromosomes other than the pair of sex chromosomes

 

Solution B.1

(a) - (iii) Study of laws of inheritance of characters

(b) - (v) Chromosomes other than the pair of sex chromosomes

(c) - (iv) A gene that can express when only in a similar pair

(d) - (ii) The alternative forms of a gene

(e) - (i) Chromosomes similar in size and shape

Question B.2
Name any two genetic diseases in humans.
Solution B.2
Colour-blindness, Thalassaemia, Sickle cell anaemia and Haemophilia (Any two)
Question B.3

Which one of the following genotypes is  homozygous dominant and which one homozygous recessive in regard to tongue rolling:
Rr, rr, RR?

Solution B.3

Homozygous dominant - RR

Homozygous recessive - rr

Question C.1

Differentiate between:

(a) Genotype and Phenotype

(b) Character and Trait

(c) monohybrid and dihybrid cross (phenotypic ratio).

Solution C.1

(a)


Phenotype

Genotype

The observable characteristic which is genetically controlled is called phenotype.

The set of genes present in the cells of an organism is called its genotype.

 

(b)


Character

Trait

Any heritable feature is called a character.

The alternative form of a character is called trait.

(b)


Monohybrid cross

Dihybrid cross

Phenotypic ratio - 3:1

Phenotypic ratio- 9:3:3:1
Question C.2
Among lion, tiger and domestic cat, all the three have the same number of 38 chromosomes, yet they have different appearances. How do you account for such differences?
Solution C.2
The characteristics of a species such as physical appearance, body functions and behavior are not only the outcome of chromosome number, but these depend on the genotype of every organism. That means the set of genes present in the organisms may very and therefore lion, tiger and domestic cat have the same number of 38 chromosomes, their characteristics (like different appearances) are the result of the genes located on the chromosomes.
Question C.3
List any three features of garden pea with their dominant and recessive traits.
Solution C.3

Character

Dominant trait

 Recessive trait

Flower Colour

Purple

White

Seed Colour

Yellow

Green

Seed Shape

Round

Wrinkled

Pod Shape

Inflated

Constricted

Flower Position

Axial

Terminal

(Any 3)

Question C.4
Explain why generally only the male child suffers from colour blindness and not the female?
Solution C.4
Colour-blindness is caused due to recessive genes which occur on the X chromosome.

Males have only one X chromosome. If there is recessive gene present on X chromosome, then the male will suffer from colour-blindness.

Females have two X chromosomes. It is highly impossible that both the X chromosomes carry abnormal gene. Hence, if one gene is abnormal and since it is recessive, its expression will be masked by the normal gene present on the other X chromosome. Females are unlikely to suffer from colour-blindness.
Question D.1

Define the following terms:

(a) Pedigree chart

(b) Variations

(c) Mutation

Solution D.1

(a) Pedigree chart: A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next. In the pedigree chart, males are shown by squares and females by circles.

(b) Variations: The small differences among the individuals of the same species are called variations.

(c) Mutation: Mutation is a sudden change in one or more genes, or in the number or in the structure of chromosomes. 

Question D.2
State the three Mendel's laws of inheritance.
Solution D.2
Mendel's laws of inheritance are:

(i) Law of Dominance Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses is the dominant character and the one that is unexpressed is the recessive one.

(ii) Law of Segregation : The two members of a pair of factors separate during the formation of gametes. The gametes combine together by random fusion at the time of zygote formation. This law is also known as 'law of purity of gametes'.

(iii) Law of Independent Assortment: When there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.
Question D.3
Does the sex of the child depend on the father or is it just a matter of chance? Discuss.
Solution D.3
The sex of the child depends on the father. The egg contains only one X chromosome, but half of the sperms contain X-chromosome whereas the other half contains Y-chromosome. It is simply a matter of chance as to which category of sperm fuses with the ovum and this determines whether the child will be male or female.

If the egg fuses with X-bearing sperm, the resulting combination is XX and the resulting child is female.

If the egg fuses with Y-bearing sperm, the resulting combination is XY and the resulting child is male.

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals
Question D.4

Distinguish between the following pairs:

(a) Karyotype and Karyokinesis

(b) Autosomes and Sex chromosomes

(c) Homozygous and Heterozygous chromosomes

Solution D.4

(a) Differences between karyotype and karyokinesis:

Karyotype

Karyokinesis

The complete set of chromosomes in the cells of an organism is its karyotype.

The division of the nucleus during mitosis is called karyokinesis.

 

(b) Differences between autosomes and sex chromosomes:

Autosomes

Sex chromosomes

1. They determine the somatic traits.

1. They determine the sex of an organism.

2. They are numbered as 1 to 22.

2. They are recognized by the letters XO, XY, ZO, ZW.

3. They show Mendelian inheritance.

3. They do not show Mendelian inheritance.

4. Human show 22 pairs of autosomes.

4. Humans show only 1 pair of sex chromosome.

 

(c) Differences between homozygous and heterozygous chromosomes:

Homozygous chromosomes

Heterozygous chromosomes

It has two same copies of the same allele coding for a particular trait.

It contains two different copies of alleles coding for a particular trait.

 

Question E.1
In a certain species of animals, black fur (B) is dominant over brown fur (b). Predict the genotype and phenotype of the offspring, when both parents are 'Bb' or have heterozygous black fur.
Solution E.1

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals 

B

b

B

BB

Bb

b

Bb

bb

Genotype - 1(Homozygous Black Fur) :2 (Heterozygous Black Fur):1 (Homozygous Brown Fur)

Phenotype - 3 (Black Fur) :1(Brown Fur)

Question E.2

Two pairs (A and B) of rabbits were crossed as given below:

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals

(a) Can you tell which coat colour (black or white) is dominant?

(b) Is the coat colour sex-linked?

Solution E.2

(a) Black

(b) No

Question E.3

Make a Punnett square for finding out the proportion of different genotypes in the progeny of a genetic cross between 

(a) A pure tall (TT) pea plant with a pure dwarf (tt) pea plant.

(b) Red flower variety of pea (RR) with white flower variety of pea (rr).

Solution E.3

(a)

 

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals 


F2 generation -

 

 

Gametes

T

t

T

TT

Tt 

t

Tt 

Tt 

 

 

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

Phenotype - 3 (Tall) :1(Dwarf)

 

(b)

 

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals 


F2 generation -

 

 

Gametes

R

r

R

RR

Rr 

r

Rr 

rr 

 

 

Genotype - 1(Homozygous red) :2 (Heterozygous red):1 (Homozygous white)

Phenotype - 3 (Red) :1(White)

Question E.4

A family consists of two parents and their five children and the pedigree chart shown below shows the inheritance of the trait colour blindness in them.

Selina Solutions Icse Class 10 Biology Chapter - Genetics Some Basic Fundamentals

(a) Who is colour blind in the parents - the Father or the Mother?

(b) How many daughters and how many sons have been born in the family?

(c) What does the child 1 indicate about this trait?

(d) On which chromosome is the gene of this trait located?

(e) Name one other trait in humans which follows a similar pattern of inheritance.

Solution E.4

(a) Father

(b) Two sons and three daughters

(c) The child 1 (daughter) is colour blind

(d) X chromosome

(e) Haemophilia