Heredity Class 10

Heredity explains why offspring resemble their parents but are not completely identical to them. It introduces genes, chromosomes, dominant and recessive traits, Mendel’s experiments and sex determination in human beings.

Heredity is the transmission of biological traits from parents to offspring. Variation refers to differences among individuals of the same species. Together, heredity and variation explain both continuity and diversity in living organisms.

Mendel’s experiments and inheritance

Gregor Mendel studied contrasting traits in pea plants. He selected true-breeding plants, performed controlled crosses and counted the traits appearing in successive generations.

Students learn about:

• Contrasting traits

• Dominant and recessive characters

• Genes as units controlling traits

• Alleles as alternative forms of a gene

• Genotype and phenotype

• Homozygous and heterozygous conditions

• Parental, first filial and second filial generations

• Monohybrid crosses

• Segregation of hereditary factors

• Expression of dominant and recessive traits

In a typical monohybrid cross, the dominant trait appears in the first generation. The recessive trait reappears in the second generation, showing that it was inherited but not expressed in the first generation.

How are traits expressed?

Genes contain information used to produce proteins. These proteins influence structures and biochemical processes, which in turn produce visible or measurable traits. A trait is therefore not created directly by a chromosome; it develops through gene-controlled cellular processes.

Inherited and acquired traits

Inherited traits are controlled by genetic information passed through reproductive cells. Acquired traits develop during an organism’s lifetime because of environment, experience or use and disuse. Acquired traits are generally not inherited because they do not change the DNA of reproductive cells.

Sex determination in human beings

Human females generally have XX sex chromosomes, while males generally have XY. Every ovum carries an X chromosome. A sperm may carry X or Y. Fertilisation by an X-bearing sperm generally produces XX, while fertilisation by a Y-bearing sperm generally produces XY.

Therefore, the chromosome contributed by the sperm determines the chromosomal sex of the child. The mother is not responsible for whether a child is male or female.

Learn Heredity with Teachoo

Teachoo provides Class 10 Heredity notes, Mendelian crosses, NCERT Solutions and important questions. Genetic crosses are solved step by step from parental traits to gametes and expected offspring.

The chapter page includes NCERT questions, in-text questions, Teachoo Questions, Exemplar MCQs, assertion–reason questions, case-based questions and previous-year questions organised by marks.

How should you prepare Heredity?

Learn each genetics term with an example. Practise drawing Punnett squares, but also write what the resulting ratio means. Never use “dominant” to mean better, stronger or more common; it only describes expression in a heterozygous condition.

Frequently Asked Questions

What is heredity?

Heredity is the transmission of biological traits from parents to offspring through genetic information.

What is the difference between genotype and phenotype?

Genotype is the genetic combination an organism carries for a trait. Phenotype is the observable expression of that trait.

Does dominant mean that a trait is more common?

No. Dominant means that the trait is expressed even when only one dominant allele is present. It does not necessarily mean more common, healthier or stronger.

Why are acquired traits generally not inherited?

Acquired traits usually affect body cells and do not alter the DNA of reproductive cells. Therefore, the change is not passed to offspring.

Who determines the chromosomal sex of a human child?

The sperm contributes either an X or a Y chromosome, while the ovum contributes X. Therefore, the chromosome contributed by the sperm determines whether the combination is XX or XY.