‘रचना-प्रयोग’ का मुख्य उद्देश्य क्या है?

व्याकरण का व्यावहारिक प्रयोग सिखाना

‘द्वितीयः’ किस प्रकार की संख्या है?

क्रमवाचक (दूसरा)

How is the sex of a child determined in humans?

The mother contributes an X chromosome; if the father contributes X the child is a girl (XX), and if Y, a boy (XY).

Why did Mendel choose the pea plant for his experiments?

Pea plants have clear contrasting traits, a short life cycle and can be easily self- or cross-pollinated.

The transmission of characters (traits) from parents to their offspring through genes carried on the chromosomes.

Why did Mendel choose the garden pea for his experiments?

The pea plant has several clear contrasting traits, a short life cycle, and can be easily self-pollinated or cross-pollinated.

Distinguish between dominant and recessive traits.

A dominant trait is expressed even when only one copy of its gene (allele) is present, while a recessive trait is expressed only when both alleles are recessive.

What ratios did Mendel obtain in a monohybrid and a dihybrid cross?

A 3:1 ratio in the F₂ generation of a monohybrid cross and a 9:3:3:1 ratio in a dihybrid cross.

What do Mendel’s dihybrid results show?

That two pairs of traits are inherited independently of each other (independent assortment of genes).

How is the sex of a child determined in humans?

The mother always contributes an X chromosome; if the father contributes an X the child is a girl (XX), and if a Y, the child is a boy (XY).

A unit of heredity, a section of DNA on a chromosome, that controls a particular trait by directing the making of a specific protein.

Why are traits inherited through genes and not acquired traits?

Only changes in the genes of the reproductive cells are passed on; traits acquired during an individual’s lifetime do not change the genes and so are not inherited.

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Chapter 8: HeredityClass 10 Science — summary, notes, extra questions & NCERT solutions

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Who is regarded as the “Father of Genetics” for his work on pea plants?

Summary

Heredity is the transmission of characteristics from parents to offspring through genes carried on chromosomes. Gregor Mendel’s experiments on pea plants laid the foundations: by tracking single traits (monohybrid crosses) and pairs of traits (dihybrid crosses), he showed that traits are controlled by factors (genes) that come in dominant and recessive forms. A dominant trait appears even when only one copy is present, while a recessive trait shows only when both copies are recessive. Mendel’s ratios — 3:1 in the F₂ generation of a monohybrid cross and 9:3:3:1 in a dihybrid cross — reveal how traits separate and recombine independently. The chapter also explains sex determination in humans, where the father’s X or Y chromosome decides the sex of the child, while the mother always contributes an X chromosome.

Mendel’s experimentsDominant and recessive traitsMonohybrid and dihybrid crossesSex determination in humansGenes and inheritance

Key terms

Gene

A unit of heredity that controls a particular trait.

Dominant trait

A trait expressed even when only one allele is present.

Recessive trait

A trait expressed only when both alleles are recessive.

Sex determination

How the sex of offspring is decided by sex chromosomes.

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Cross two parents and see the ratios

Parent 1Parent 2

	A	a
A	AA	aA
a	aA	aa

Genotype ratio

1 AA : 1 aa

Phenotype ratio

1 dominant : 1 recessive

Capital allele (A) is dominant; offspring showing A_ have the dominant trait.

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Gene

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Meaning1 / 4

A unit of heredity that controls a particular trait.

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Chapter 8: HeredityClass 10 Science — summary, notes, extra questions & NCERT solutions

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