Understand Punnett square crosses, law of segregation, independent assortment, and XX/XY human sex determination for Class 10 boards.
Heredity and Evolution explores how biological traits are transmitted across generations from parents to offspring. Gregor Johann Mendel's hybridization experiments on garden pea plants (Pisum sativum) founded modern genetics.
Mendel's Monohybrid Cross: Crossing pure tall (TT) and dwarf (tt) pea plants produces all tall (Tt) plants in the F1 generation. Self-pollination of F1 yields F2 generation with Phenotypic Ratio 3:1 (3 Tall : 1 Dwarf) and Genotypic Ratio 1:2:1 (1 TT : 2 Tt : 1 tt), demonstrating the Law of Segregation of alleles.
Dihybrid Cross & Independent Assortment: Crossing plants differing in two traits (Round Yellow RRYY x Wrinkled Green rryy) gives an F2 Phenotypic Ratio of 9:3:3:1 (9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green).
Sex Determination in Humans: Females possess XX chromosomes; Males possess XY chromosomes. Father's sperm carrying either X or Y chromosome determines the biological sex of the child with a 50% probability. Dr. Aarzoo Saini guides Class 10 students through genetics crosses at We-Gyaan Classes.
Key Takeaways for Students
- Draw Punnett squares for monohybrid (3:1 ratio) and dihybrid (9:3:3:1 ratio) genetic crosses.
- Differentiate Phenotype (observable physical trait) from Genotype (genetic allele makeup).
- State Mendel's Law of Segregation and Law of Independent Assortment.
- Explain chromosomal basis of human sex determination with 50% gender probability.
Authored by Dr. Aarzoo Saini
Founder & Lead Educator at We-Gyaan Classes Roorkee, with over 15 years of teaching excellence in Science and Chemistry for Board Exams, NEET, JEE, and CUET.