Genetics and Evolution is a core topic in NEET Biology, with a high number of predictable and conceptual questions. It connects inheritance patterns, gene interactions, and evolutionary biology—all essential for understanding the diversity of life. This blog offers a complete, NEET-focused guide to help aspirants revise effectively and conceptually.

Genetics and Evolution – Complete NEET 2026 Notes 

1. Heredity and Variation

Heredity is the transmission of traits from one generation to the next, governed by genes. Variation is the difference in traits among individuals, which arises from:

• Mutation
• Recombination
• Environmental factors

Variation is the foundation of natural selection and thus, evolution.

2. Mendelian Inheritance (Basic Principles)

Gregor Mendel, the father of genetics, performed hybridization experiments on Pisum sativum (pea plants). He discovered 3 fundamental laws:

Law of Dominance

• One allele can mask the expression of another.
• Phenotype shows the dominant trait.

Law of Segregation

• Alleles separate during gamete formation.
• Each gamete carries only one allele for each gene.

Law of Independent Assortment

• Genes for different traits assort independently.
• Seen in dihybrid crosses.

NEET Tip: Remember the phenotypic ratio for Mendel’s dihybrid cross: 9:3:3:1.

3. Deviations from Mendelism

All traits don’t follow simple dominance. Some traits exhibit non-Mendelian inheritance:

Incomplete Dominance

• One allele is partially dominant over the other.
• Example: Red (RR) × White (rr) = Pink (Rr) in snapdragon flowers.

Co-dominance

• Both alleles express equally.
• Example: AB blood group, where both A and B antigens appear.

Multiple Alleles

• A gene has more than two allelic forms.
• Example: Blood groups (IA, IB, i).

Pleiotropy

• A single gene controls multiple traits.
• Example: Phenylketonuria (affects skin, hair, brain function).

4. Polygenic Inheritance (Quantitative Traits)

Traits like skin color, height, and eye color are controlled by multiple genes (polygenes). These show continuous variation and are influenced by environmental factors.

• Example: Skin color is determined by 3 separate gene pairs.
• Phenotypes follow a bell-shaped curve.

NEET Insight: Polygenic inheritance ≠ multiple alleles.

Polygenic = many genes, one trait

Multiple alleles = one gene, many forms

5. Chromosome Theory of Inheritance

Sutton and Boveri (1902) proposed that genes are located on chromosomes, and chromosomes segregate and assort independently during meiosis—explaining Mendel's laws at the cellular level.

Key Points:

• Chromosomes carry genes.
• Genes have specific loci (positions).
• Chromosomes occur in pairs (diploid organisms).

6. Chromosomes and Genes

• Genes are segments of DNA that code for proteins.
• Each gene is present on a specific locus of a chromosome.
• Humans have 23 pairs (46 chromosomes): 22 pairs of autosomes + 1 pair of sex chromosomes (XX or XY).

7. Sex Determination

In Humans:

• Males: XY → Determine the sex of the offspring
• Females: XX
• If sperm carries X → girl (XX)
• If sperm carries Y → boy (XY)

In Birds:

• Female: ZW
• Male: ZZ
• Sex is determined by the female.

In Honeybee:

• Males (drones): haploid, develop from unfertilized eggs (parthenogenesis)
• Females (workers/queen): diploid, develop from fertilized eggs

8. Linkage and Crossing Over

Linkage

• Genes located on the same chromosome are inherited together.
• Discovered by Morgan in Drosophila (fruit fly).
• Tightly linked genes = less recombination
• Loosely linked genes = more recombination

Crossing Over

• Exchange of genetic material between homologous chromosomes during meiosis.
• Leads to new gene combinations (recombinants).
• Occurs in Prophase I of meiosis.

9. Sex-Linked Inheritance

Traits controlled by genes located on sex chromosomes, especially the X chromosome.

Examples:

• Haemophilia: Blood clotting disorder (X-linked recessive)
• Color blindness: Inability to distinguish red-green colors (X-linked recessive)

NEET Tip: These disorders are more common in males (XY), as they lack a second X chromosome to compensate.

10. Mendelian Disorders in Humans

Thalassemia

• Autosomal recessive disorder.
• Affects hemoglobin production.
• Leads to anemia, weakness, fatigue.
• Two types: Alpha and Beta Thalassemia.
• Diagnosis: Blood tests, prenatal screening.

11. Chromosomal Disorders in Humans

Caused by numerical or structural abnormalities in chromosomes.

Down’s Syndrome (Trisomy 21)

• Cause: Extra chromosome 21 (47 chromosomes)
• Features: Mental retardation, short stature, flat facial profile

Turner’s Syndrome (XO)

• Cause: Only one X chromosome (45 chromosomes)
• Female with underdeveloped ovaries, short stature, webbed neck

Klinefelter’s Syndrome (XXY)

• Cause: Extra X chromosome in males (47 chromosomes)
• Features: Gynecomastia, infertility, reduced body hair

Evolution: A Quick Glance

Though detailed evolution is in the next chapter, NEET basics include:

• Variation + Natural selection = Evolution
• Mutation is the ultimate source of genetic variation.
• Fossil records, comparative anatomy, and molecular biology support the theory of evolution.

NEET-Ready Summary Table

Final Words from Science Coat

Understanding Genetics and Evolution is not just about memorizing terms, but recognizing how life functions at the genetic level. Whether it’s Mendel’s pea plants or human chromosomal disorders, each concept builds your foundation for advanced biology and medical sciences.

At ScienceCoat.com, we simplify NEET content with clarity, concept, and confidence. Keep revising with us for more high-yield notes and chapter summaries!

Thank you for exploring “Genetics and Evolution – Complete NEET 2026 Notes” with us at Science Coat. We hope these NEET-focused, high-value notes helped you understand the concepts better and made your preparation easier.

Our mission is to make science simple, smart, and accessible for every NEET aspirant. If this post helped you, don’t forget to share it with your friends and save it for revision.

Keep learning. Keep growing. Your NEET 2026 success is just a concept away.

— Team Science Coat

© 2025 Science Coat. All rights reserved.
Content on this page is original and intended for educational use only. Unauthorized copying or reproduction is strictly prohibited.