Heredity and Evolution Class 10 Notes

We will teach students about heredity and evolution in depth by demonstrating the importance of various types of reproductions, genes, traits, and other factors.

Heredity and Evolution Class 10 Notes Science Chapter 9

Acquired and Inherited Traits:

Any attribute acquired by an organism throughout its existence as a result of external circumstances is not passed down to its progeny. These characteristics are referred to as acquired qualities. For instance, the manner a person speaks or the abilities he or she possesses. Because these modifications do not influence germ cells, they cannot be passed down from generation to generation.

An inherited trait is defined as a trait that is genetically inherited or passed down from one generation to the next. Consider the color of one’s eyes or skin.

Mendel’s Work

Gregor Johann Mendel, also regarded as the “Father of Genetics,” was an Austrian monk who studied pea plants to better understand heredity.

His research created the groundwork for current genetics.

The Law of Dominance, The Law of Segregation, and The Law of Independent Assortment were his three primary laws of inheritance.

Dominant traits

Dominant qualities are traits that manifest themselves in an organism in every possible combination and are visible.

The tall trait in pea plants tends to express more than the short trait in Mendel’s experiment.

As a result, the plant’s tall trait is considered to be dominant over its short trait.

Recessive traits

Recessive traits are those that are not expressed in the presence of a dominant allele.

So, if a dominant allele occurs, a recessive character/trait is present in an organism but cannot be detected.

Monohybrid cross

Monohybrid crosses occur when just one character is taken into account when crossing two organisms.

Monohybrid ratio refers to the character ratio that results from this cross at the F2 generation.

E.g., After crossing a tall plant (TT) with a dwarf plant (tt), the F2 generation yields three tall: one short plant.

As a result, the monohybrid ratio is 3:1.

The plant’s height is taken into account one at a time.

Dihybrid cross

A dihybrid cross occurs when two characters are taken into account while crossing two organisms.

The dihybrid ratio refers to the character ratio that results from this cross at the F2 generation.

For example, if a round and green pea plant is crossed with a wrinkled and yellow pea plant, the result is a wrinkled and yellow pea plant.

Plants in the first generation would all be round and green peas.

When we cross the same for an F2 generation, we get four different character combinations in the ratio 9:3:3:1.

As a result, the dihybrid ratio is 9:3:3:1.

Mendel’s Laws

According to the Law of Dominance, a gene has two opposing alleles, one of which is always expressed in the organism.

It’s known as the dominant gene, and it can be expressed in any combination.

The Law of Segregation states that characteristics are entirely segregated during the creation of gametes, with no allele mixing.

The Law of Independent Assortment states that during gamete production, characteristics can segregate independently of various characters.

Determination of sex

The sex of a newly born creature is determined by a variety of mechanisms. It might be based on the temperature at which the fertilized eggs are stored, as in a few reptiles, or it could be based on fluctuations in temperature, as in snails. The sex of a newborn infant in humans, on the other hand, is mostly decided by the genes inherited from the parents.

In humans, all of the chromosomes are not paired. A pair of 22 chromosomes is usually present, with one pair coming from each of the parents. All of the qualities are mostly determined by them.

The sex chromosomes are a pair of chromosomes that differ between males and females. Females have a proper pair of chromosomes, which are referred to as X chromosomes, whereas men have an X chromosome and its Y chromosome pair. Women have the genotype XX, while men have the genotype XY.

When we examine the male and female inheritance patterns, we can see that the child inherits X from their mother by default, and the child’s sex is determined by which set of sex chromosomes is inherited from the father.

If the child inherits X, the pair becomes XX, and the child is a girl; if the child inherits Y, the pair becomes XY, and the child is a boy.

Charles Darwin

Charles Darwin was an English naturalist and biologist known as the “Father of Evolution.”

He wrote his theory of evolution during a five-year voyage to Galapagos Island aboard the HMS Beagle.

In 1859, he released Origin of Species, a book in which he detailed his theory of evolution.


Evolution is the gradual change in a population’s heritable features over numerous generations. These changes may result in the emergence of new species, or species may evolve to become more adapted to their surroundings.

Robin Singh

Robin Singh is education professional tutor of NCERT. I have good knowledge of CBSE all subjects. Expert in maths, physics and chemistry. if students have any doubt about NCERT Solutions so contact us

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