Class 12 Biology DPP — Ch 4 — Principles of Inheritance and Variation | 22 July 2026

Assertion (A): A test cross is used to determine the genotype of an organism showing a dominant trait.
Reason (R): It involves crossing with a homozygous recessive individual.

Choose the correct option:

A. Both A and R are true, and R is the correct explanation of A B. Both A and R are true, but R is NOT the correct explanation of A C. A is true, but R is false D. A is false, but R is true

📝 SolutionA test cross with a homozygous recessive reveals the unknown genotype from the offspring ratio. R correctly explains how the test cross achieves A.

Colour blindness and haemophilia are examples of:

A. autosomal disorders B. sex-linked (X-linked) disorders C. chromosomal number disorders D. nutritional disorders

📝 SolutionColour blindness and haemophilia are X-linked recessive disorders, more common in males.

Down's syndrome is caused by an extra copy of chromosome number:

A. 18 B. 21 C. 23 D. 13

📝 SolutionDown's syndrome (trisomy 21) results from an extra copy of chromosome 21.

The number of chromosomes in a normal human somatic cell is:

A. 23 B. 44 C. 46 D. 48

📝 SolutionHuman somatic cells have 46 chromosomes (23 pairs).

In humans, the sex of the child is determined by the:

A. mother's chromosome B. father's sperm (X or Y) C. size of egg D. environment

📝 SolutionThe father's sperm carries either an X or Y chromosome, determining the sex of the child (XX female, XY male).

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Class 12 · Biology

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