Lecture Notes on Heredity

Introduction

• Lecturer: प्रशांत भैया
• Topic: Heredity
• Questions addressed:
  • Why do people have different eye colors? (e.g., black, brown, blue)
  • Why do people have different hair colors? (e.g., black, brown)
  • Why do people have different heights?

What is Heredity?

• Definition: The transfer of characters from parents to offspring.
• Important Terms:
  • Father of Genetics: Gregor Mendel
  • Mendel's Experiments: Key experiments conducted on pea plants.

Important Concepts

1. Heredity: Transfer of traits from parents to offspring.
2. Inheritance: The process through which characters pass from one generation to another.
3. Traits: Observable characteristics.
   • Types: Acquired Traits vs Inherited Traits
   • Differences:
     • Acquired traits are not inherited and do not get passed to progeny.
     • Inherited traits are inherited and passed to progeny.
4. Genes and Alleles:
   • Gene: Unit of heredity that transfers characteristics from parents to offspring.
   • Allele: Different forms of a given gene responsible for variations in which a trait can be expressed.
5. Phenotype and Genotype:
   • Phenotype: Observable physical characteristics.
   • Genotype: Genetic makeup responsible for a trait.
6. Homozygous and Heterozygous:
   • Homozygous: Having two identical alleles (e.g., TT or tt).
   • Heterozygous: Having two different alleles (e.g., Tt).
7. F1 and F2 Generation:
   • F1 Generation: Result of cross-fertilization between parents.
   • F2 Generation: Result of self-fertilization of F1 generation.
8. Haploid and Diploid:
   • Haploid: Cells with single set of chromosomes.
   • Diploid: Cells with paired chromosomes.

Mendel’s Experiments

1. Monohybrid Cross:
   • Studied a single trait (e.g., plant height).
   • F1 Generation: All tall plants.
   • F2 Generation: 3:1 ratio of tall to short plants.
2. Dihybrid Cross:
   • Studied two traits at the same time (e.g., seed color and seed shape).
   • F1 Generation: All yellow and round seeds.
   • F2 Generation: 9:3:3:1 ratio.

Mendel’s Laws of Inheritance

1. Law of Dominance:
   • Some alleles are dominant and cover up the recessive alleles.
2. Law of Segregation:
   • Alleles separate during gamete formation, each gamete carries only one allele for each gene.
3. Law of Independent Assortment:
   • Alleles for different traits are distributed to gametes independently.

How Traits Get Expressed (Transfer of Traits)

• Genes and their alleles determine traits.
• During reproduction, parents pass one allele for each gene to their offspring.
• Variation occurs due to errors in DNA duplication.
• Dominant alleles determine the traits expressed in the offspring.

Sex Determination

• Process determining the sex of an individual based on genetic material.
• Human Chromosomes:
  • 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes.
  • Male: XY, Female: XX.
• Determining Offspring Sex:
  • Male gamete (X or Y) combines with female gamete (X).
  • Result: XX (Female) or XY (Male).

Key Points to Remember

• Mendel's work on pea plants is foundational to our understanding of genetics.
• Genes are the basic unit of heredity; alleles are variations of these genes.
• Mendel’s Laws explain how traits are inherited and expressed.
• Sex determination in humans depends on the combination of X and Y chromosomes from parents.

Exam Preparation Tips

• Focus on Mendel’s experiments and laws.
• Practice monohybrid and dihybrid crosses.
• Understand the process of sex determination thoroughly.

---

End of Notes