NCERT Solutions Class 10th Science Chapter – 8 Heredity Notes

June 2, 2022

NCERT Solutions Class 10th Science Chapter – 8 Heredity

Textbook	NCERT
Class	10^th
Subject	Science
Chapter	8^th
Chapter Name	Heredity
Category	Class 10th Science
Medium	English
Source	Last Doubt

NCERT Solutions Class 10th Science Chapter – 8 Heredity Notes In This Chapter we will learn about Heredity, Heredity and Evolution, Law of Dominance, Law of Segregation, Male, Female, Sex Determination in Humans and more such things for more knowledge about this Chapters read their Notes.

NCERT Solutions Class 10th Science Chapter – 8 Heredity

Chapter – 8

Heredity

Notes

Heredity – The transfer of traits from one generation to the next is termed heredity. Genes are the functional units of heredity that transfer characteristics from parents to offspring. Genes are short stretches of DNA that code for a specific protein or RNA.

Heredity and Evolution

• Heredity
• Sex determination in humans
• Evidences of evolution
• Speciation

1. Heredity (Monohybrid Cross)

• Law of Dominance
• Law of Independent Assortment

(i) Law of Dominance (F1 Generation)

• Phenotype – All Dominant
• Genotype – Dominant

Law of Segregation

• Phenotype – 3:1
• Genotype – 1:2:1

(ii) Law of Independent Assortment (Dihybrid Cross)

F1 Generation	F2 Generation
Phenotype – All Dominant	Phenotype – Dominant Traits.
Genotype – Dominant	genotype – 9:3:3:1

2. Sex Determination in Humans

Male

• Male 22 + XY
• 22 Autosomes
• XY Sex chromosomes
• Child who inherits Y chromosomes from his father: Boy (xy)

Female

• Female 22 + XX
• 22 Autosomes
• XX Sex chromosomes
• Child who inherits X chromosome from & his father: Girl (xx)

3. Evidences of Evolution

Morphological and Anatomical

• Analogous organs
• Homologous organs

Vestigeal

• Organs present but not functional

Palaeontological

• Study of fossils

4 Speciation

Factors Affecting:

• Genetic Drift
• Reproductive Isolation
• Geographical isolation
• Natural selection.

Genetics

Deals with the study of

Heredity	Variation
The transmission of characters/traits from one generation to the next generation.	The differences in the characters/traits between the parent and offspring.

Variation

Somatic variation	Gametic variation
• Takes place in the body cells.	• Takes place in the gametes/ Reproductive cells.
• Neither inherited nor transmitted.	• Inherited as well as transmitted.
• Also known as acquired traits.	• Also known as inherited traits.
Example, boring of pinna, cutting of tails in dogs.	Example, human height, skin colour.

Accumulation of Variation during Reproduction

1. Asexually
2. Sexually (Appear during reproduction When ever organism multiply)

Asexually

• Variations are fewer
• Occurs due to small inaccuracies in DNA copying. (Mutation)

Sexually

• Variations are large
• Occurs due to crossing over, separation of chromosomes, mutation.

Importance of Variation

(i) Depending upon the nature of variations different individuals would have different kinds of advantage.
Example – Thermostatic Bacteria that can withstand heat will survive better in a heat wave.

(ii) Main advantage of variation to species is that it increases the chances of its survival in a changing environment.
Free ear lobes and attached ear lobes are two variants found in human populations.

NCERT Solutions Class 10th Science Chapter - 9 Heredity and Evolution Notes

Mendel’s Experimental Material – He chose Garden Pea (Pisum sativum) as his experiment material because of

(i) Availability of detectable contrasting traits of several characters.
(ii) Short life span of the plant.
(iii) Normally allows self-fertilisation but cross-fertilisation can also be carried out.
(iv) Large no. of seeds produced.

Mendel’s Experiments – Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time).

Observations of Monohybrid Cross

(i) All F₁ progeny were tall, no medium height plant. (Half way characteristic)
(ii) F₂ progeny 1/4 were short, ¾ were tall.
(iii) Phenotypic ratio F₂– 3 : 1 (3 tall: 1 short)
(iv) Genotypic ratio F₂– 1 : 2 : 1 (TT : Tt : tt / 1 : 2: 1)

Conclusions

1. TT and Tt both are tall plants while tt is a short plant.
2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
3. Characters/traits like ‘T’ are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed).

F2 gametes →

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

Phenotypic Ratio

1. Round, yellow: 9
2. Round, green: 3
3. Wrinkled, yellow: 3
4. Wrinkled, green: 1

Observations

(i) When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds.

(ii) Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow and wrinkled green) seeds plants in the ratio of 9 : 3 : 3 : 1.

9 (Round/yellow) : 3 (Round/green) : 3 (Wrinkled/yellow) : 1 (Wrinkled/green)

Conclusions

1. Round and yellow seeds are Dominant characters.
2. Occurrence of new phenotype combinations show that genes for round and yellow seeds are inherited independently of each other.

Mendel’s Law of Inheritance – Based on his hybridisation experiments, mendal proposed the laws of inheritance.

1. Law of dominance – This law states that when two alternative forms of a trait or character (genes or alleles) are present in as organism, only one facter expresses itself in F, progery and is called dominant while the other that remains masked is called recessive. Characters are controlled by discrete units called factors. Factors occur in pairs.

2. Law of segregation or law of purity of gametes.

This law states that the facters of alleles of a pair segregate from each other durting gamete formation such that a example recieve only one of the factors. They do not show any blending but simply remain together.

Homozygous parent produces all gametes that are similar, heterozygous parent produces two types of gametes, each having one allele in equal proportion.

3. Law of independent assortment –

This law states that the two factors of each character assort or separate out independent of the factors of other characters at the time of gamete formation and get randomly rearranged in the offsprings producing both parental and new combination of characters.

When two pairs of traits are combined in a hybrid, segreration of one pair of character is independent of the other pair of characters.

How do these traits get expressed

(i) Cellular DNA (Information source)
(ii) For synthesis of Proteins (Enzyme)
(iii) Works efficiently More Hormone
(iv) produced
(v) Tallness of plant

SEX DETERMINATION – Determination of sex of an offspring.

FACTORS

Responsible for Sex Determination

1. Environmental
2. Genetic

(i) Environmental – In some animals, the temperature at which the fertilized eggs are kept decides the gender.

Example – in turtle

(ii) Genetic – In some animals like humans gender of individual is determined by a pair of chromosomes called sex chromosome.

XX – Female
XY – Male