Class 10 Science - Heredity
Heredity is the transmission of traits from parents to offspring.
1. Mendel's Contribution
Gregor Mendel, the "Father of Genetics," worked on Pea Plants (Pisum sativum) because they had clear contrasting traits.
Mendel's Laws:
- Law of Dominance: In a cross between two variants, one trait (dominant) masks the other (recessive).
- Law of Segregation: Alleles separate during gamete formation.
- Law of Independent Assortment: Traits are inherited independently of each other.
Monohybrid Cross:
Crossing tall (TT) and dwarf (tt) plants.
- F1 Generation: All Tall (Tt).
- F2 Generation Ratio: 3:1 (Phenotypic) and 1:2:1 (Genotypic).
2. How are Traits Expressed?
DNA is the information source for making proteins. A section of DNA that provides information for one protein is called a Gene. Proteins control the appearance of a trait.
3. Sex Determination in Humans
- Total chromosomes: 23 pairs (46 total).
- 22 pairs are Autosomes.
- 1 pair is Sex Chromosome.
- Females: XX
- Males: XY
Mechanism: The sex of the child is determined solely by the father. If he contributes an 'X' chromosome, it's a girl; if 'Y', it's a boy.
4. Evolution (Basic Concepts)
Note: In 2026 CBSE curriculum, Evolution sections are often reduced. Focus on:
- Speciation: Formation of new species due to geographical isolation and genetic drift.
- Acquired vs Inherited Traits: Changes in non-reproductive tissues (Acquired) are not passed on.
🧬 Key Terms to Remember
- Genotype: Genetic makeup (e.g., Tt).
- Phenotype: Physical appearance (e.g., Tall).
- Alleles: Alternative forms of a gene.
Draw the Punnett Square clearly in your exam! 🧪🧫
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