Principles of Genetic Inheritance and Variation

Aug 2, 2024

Principles of Inheritance and Variation - Lecture Notes

Lecture Introduction

  • Introduction to Genetics
  • One-shot Principles of Inheritance and Variation
  • Importance of Genetics and study methods
  • Importance of NCERT

Mendelian Genetics

Mendel's Experiments

  • Experiments on pea plants (Pisum sativum)
  • Focus on 7 contrasting characters
  • Monohybrid and Dihybrid cross

Mendelian Laws

  • Law of Dominance: In a pair of genes, the dominant allele masks the other
  • Law of Segregation: Alleles segregate into different gametes
  • Law of Independent Assortment: Different gene pairs assort independently

Key Terms

  • Gene: A segment of DNA that forms a protein
  • Allele: Different forms of a gene
  • Homozygous: Same type of alleles (TT or tt)
  • Heterozygous: Different alleles (Tt)

Non-Mendelian Genetics

Incomplete Dominance

  • Mixed effect of both alleles
  • Example: Red and white flowers in Snapdragons -> pink flowers

Co-dominance

  • Both alleles are clearly expressed
  • Example: ABO blood group system (IA and IB)

Multiple Alleles

  • A gene can have multiple alleles
  • Example: Blood group alleles (IA, IB, i)
  • Calculation formula: n + 1 and n (n + 1)/2

Polygenic Inheritance

  • A character controlled by multiple genes
  • Example: Human skin color
  • Formula: 2n+1 and 3n

Pleiotropy

  • One gene shows multiple phenotypic effects
  • Example: Phenylketonuria (PKU)

Chromosomal Theory of Inheritance

  • Proposed by Sutton and Boveri
  • Genes are located on chromosomes
  • Similarity between Chromosomal behavior and Mendelian laws

Linkage and Recombination

  • Linked genes located on the same chromosome
  • Gene mapping through recombination frequency

Sex Determination

Human

  • XY system: Males (XY), Females (XX)

Birds

  • ZW system: Females (ZW), Males (ZZ)

Honeybees

  • Haplodiploidy system: Males (haploid), Females (diploid)

Genetic Disorders

Chromosomal Disorders

  • Down Syndrome: Trisomy 21
  • Klinefelter Syndrome: XXY
  • Turner Syndrome: XO

Gene Disorders

  • Sickle Cell Anemia: Point mutation in hemoglobin gene
  • Phenylketonuria (PKU): Defect in phenylalanine metabolism
  • Thalassemia: Quantitative defect in hemoglobin
  • Hemophilia: Blood clotting defect
  • Color Blindness: Inability to distinguish red and green
  • Albinism: Lack of melanin production

Pedigree Analysis

  • Pedigree charts for tracing inheritance
  • Symbols: Squares (males), Circles (females)
  • Filled shapes for affected individuals
  • Autosomal Dominant: Affected every generation
  • Autosomal Recessive: Skips generations
  • X-linked Recessive: More males affected

Important Formulae

  • Types of gametes: 2^n
  • Recombination frequency: (Number of recombinant offspring / Total offspring) * 100
  • Polygenic inheritance: 2n+1
  • Multiple alleles: n(n+1)/2

Conclusion

  • Comprehensive overview of inheritance principles
  • Importance of understanding Mendelian and non-Mendelian genetics
  • Application in genetic disorders and evolution

Homework

  • Pedigree analysis problems
  • Solving inheritance-based questions using provided formulae

Next Session

  • Molecular basis of inheritance
  • Detailed study on DNA, RNA, and their roles in genetics

Principles of Inheritance and Variation chapter provides fundamental knowledge essential for understanding advanced genetics topics.