Statement I: Mendel studied seven pairs of traits. Statement II: Characters were seed shape/colour, flower colour, pod shape/colour, flower position and stem height.

Both Statement I and Statement II are correct

Statement I is correct but Statement II is incorrect

Statement I is incorrect but Statement II is correct

Both Statement I and Statement II are incorrect

Among the following characters, which one was not considered by Mendel in his experiments on pea?

Trichomes - Glandular or non-glandular

Mendel's Laws

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NCERT Class 12 · Principles of Inheritance and Variation · 6 NEET questions

Mendel did not just study peas; he decoded the mathematical probability of your existence. Most students fail because they confuse the Law of Segregation with Independent Assortment. If you cannot distinguish between gamete purity and random distribution, you are not ready for the exam.

The idea

Mendel’s Laws are fundamental. The Law of Dominance states that in a heterozygous condition, only the dominant allele expresses its phenotype. The Law of Segregation asserts that alleles separate during gamete formation, ensuring each gamete receives only one allele. The Law of Independent Assortment states that the segregation of one pair of traits is independent of another pair during gamete formation.

Why it matters

These laws exist as the mathematical and logical rules governing how discrete genetic units (genes) are passed from parents to offspring.

NEET lens

NEET focuses on the dihybrid cross ratio 9:3:3:1 and the test cross. Memorize that Independent Assortment applies only to genes on different chromosomes. Do not confuse phenotypic ratios with genotypic ratios. Expect at least one question on exceptions like incomplete dominance or codominance.

Clinical significance

When segregation fails, nondisjunction occurs, leading to aneuploidy. This is the root cause of conditions like Down syndrome, where an extra chromosome 21 persists. Understanding these laws is the only way to grasp the mechanism of chromosomal disorders.

Introduction

Mendel's Laws of Inheritance describe the patterns of transmission of heritable traits, derived from Mendel's pea plant experiments (1856–1863): (1) Law of Segregation and (2) Law of Independent Assortment, forming the foundation of classical genetics.

Core concept

Mendel's experimental system: Pisum sativum (garden pea). 7 pairs of contrasting characters (seed shape, seed colour, pod shape, pod colour, flower colour, flower position, plant height). True-breeding lines. Controlled pollination. Counted large numbers of offspring. Law 1: Law of Segregation (Law of Purity of Gametes): Each individual has two alleles for each trait. Alleles separate (segregate) during gamete formation. Each gamete receives only one allele. Alleles come together randomly at fertilization. Basis: meiosis separates homologous chromosomes → each gamete gets one. Law 2: Law of Independent Assortment: Alleles of different genes assort independently during gamete formation (each gene pair segregates independently of others). Basis: homologous chromosomes of different pairs segregate independently at meiosis I. Applies only when genes are on different chromosomes (not linked).

Go deeper

Mendel's terminology: Dominant: allele expressed in heterozygote (uppercase, e.g., T). Recessive: allele not expressed in heterozygote (lowercase, e.g., t). Phenotype: observable trait. Genotype: genetic composition. F1: first filial generation (hybrids). F2: offspring of F1 × F1. Monohybrid cross: one character, F2 = 3:1 (phenotypic). Dihybrid cross: two characters, F2 = 9:3:3:1 (phenotypic). Genotypic ratio: monohybrid F2 = 1:2:1.

From Class 10

Gregor Mendel's experiments with pea plants revealed the fundamental principles of inheritance — how traits pass from parents to offspring through discrete units we now call genes.