Genetics – NEET Notes

1. Introduction to Genetics

• Genetics is the study of heredity and variation.
• Gregor Mendel is known as the Father of Genetics.
• Genes are the units of heredity located on chromosomes.

2. Mendel’s Laws of Inheritance

• Law of Dominance: One allele can mask the expression of another.
• Law of Segregation: Alleles separate during gamete formation.
• Law of Independent Assortment: Genes for different traits assort independently.

3. Important Terms

• Allele: Different forms of a gene.
• Homozygous: Identical alleles (AA or aa).
• Heterozygous: Different alleles (Aa).
• Phenotype: Physical expression of a trait.
• Genotype: Genetic makeup of a trait.

4. Monohybrid and Dihybrid Cross

• Monohybrid ratio: 3:1 (phenotypic), 1:2:1 (genotypic)
• Dihybrid ratio: 9:3:3:1 (phenotypic)

5. Non-Mendelian Inheritance

• Incomplete Dominance: Blending of traits (e.g., red × white = pink).
• Codominance: Both alleles are expressed (e.g., AB blood group).
• Multiple Alleles: More than two alleles for a trait (e.g., ABO blood group).

6. Sex Determination

• Humans: XX (female), XY (male)
• Birds: ZW (female), ZZ (male)

7. Pedigree Analysis

• Tool used to study inheritance over generations.
• Helps identify autosomal dominant, autosomal recessive, and sex-linked traits.

8. Genetic Disorders

• Thalassemia: Autosomal recessive disorder of hemoglobin.
• Hemophilia: Sex-linked recessive bleeding disorder.
• Down Syndrome: Trisomy 21 – extra chromosome 21.