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

Genetics - Some Basic Fundamentals Exercise Ex. 1

Solution A.1

a) 3 : 1

Solution A.2

(a) all tall

Solution A.3

(c) independent assortment

Solution A.4

(c) Gs and gs 

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

Solution B.2

Colour-blindness, Thalassaemia, Sickle cell anaemia and Haemophilia (Any two)

Solution B.3

Homozygous dominant - RR

Homozygous recessive - rr

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

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.

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)

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.

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. 

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.

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.

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.

 

Solution E.1

 

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)

Solution E.2

(a) Black

(b) No

Solution E.3

(a)

 

 


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)

 

 


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)

Solution E.4

(a) Father

(b) Two sons and three daughters

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

(d) X chromosome

(e) Haemophilia

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