Class 10 Science Heredity Notes

Class 10 Science Heredity Notes

Introduction

  • Heredity: The process by which traits and characteristics are passed from parents to offspring.
  • Explains why children resemble their parents but are not identical.

1. Mendel’s Experiments

  • Gregor Mendel: Father of Genetics, studied pea plants.
  • Observations: Traits are inherited in a predictable pattern.
  • Laws of Heredity:
    1. Law of Segregation: Two alleles of a trait segregate during gamete formation, only one allele goes to a gamete.
    2. Law of Independent Assortment: Different traits are inherited independently of each other.

2. Variation

  • Definition: Differences in traits among individuals of the same species.
  • Types:
    1. Intra-specific variation: Differences within the same species (e.g., height, eye color).
    2. Inter-specific variation: Differences between species (e.g., humans vs. dogs).
  • Causes:
    • Genetic: Mutation, recombination
    • Environmental: Climate, nutrition

3. Sex Determination

  • Humans: Determined by sex chromosomes (X and Y)
    • Female → XX
    • Male → XY
  • Offspring: 50% chance of being male or female

4. Chromosomes and Genes

  • Chromosome: Thread-like structure in nucleus, carries genes
  • Gene: Unit of heredity controlling a specific trait
  • Humans have 46 chromosomes (23 pairs)
  • Alleles: Different forms of a gene (dominant or recessive)

5. Dominant and Recessive Traits

  • Dominant trait: Expressed even if only one allele is present
  • Recessive trait: Expressed only when both alleles are recessive
  • Example:
    • Dominant: Brown eyes (B)
    • Recessive: Blue eyes (b)
    • Bb → Brown eyes

6. Punnett Square (Predicting Offspring)

  • Diagram used to predict genetic combinations of offspring
  • Helps determine probability of traits