(p+q)2= p2+2pq+q2=1 represents Hardy Weinberg equation. It is used in:

The correct answer is Option (1) → Population genetics

The Hardy-Weinberg principle deals with allele frequencies in a population: p is the frequency of one allele and q of the other. Without disturbing factors these stay constant, and p² + 2pq + q² = 1 gives the genotype frequencies.

Option (1) Population genetics — Correct. The Hardy-Weinberg equation, p² + 2pq + q² = 1, says that allele frequencies in a population stay constant from generation to generation unless something disturbs them. It is used in population genetics, the study of genes and their frequencies in populations.

Option (2) Mendelian genetics — Incorrect. Mendelian genetics follows the crosses of individual parents and their offspring, not a whole population.

Option (3) Biometrics — Incorrect. Biometrics is the measurement of body features, such as fingerprints, for identification.

Option (4) Molecular genetics — Incorrect. Molecular genetics studies the structure and working of DNA and genes inside cells.

NCERT Extract:
Hardy-Weinberg Principle – “In a given population one can find out the frequency of occurrence of alleles of a gene or a locus. This frequency is supposed to remain fixed and even remain the same through generations. Hardy-Weinberg principle stated it using algebraic equations. This principle says that allele frequencies in a population are stable and is constant from generation to generation. The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium.”