Genetics Lecture - Chapter 3

Overview

This lecture is divided into three units:

• Unit 1: Basic Mendelian Genetics
• Unit 2: Autosomes and Sex Chromosomes
• Unit 3: Non-Mendelian Inheritance

Unit 1: Basic Mendelian Genetics

Key Concepts

• Gregor Mendel's Experimentation

  • Established transmission genetics.
  • Used pea plants to discover principles of heredity, known as Mendelian genetics.
  • Conducted between 1856 and 1863 with ~28,000 pea plants.
  • Identified "particles" (now known as chromosomes) responsible for trait inheritance.

• Mendel's Laws of Inheritance

  • Law of Dominance: Dominant alleles mask recessive ones in heterozygotes.
  • Law of Segregation: Alleles separate during gamete formation and recombine at fertilization.
  • Law of Independent Assortment: Traits are inherited independently.

Genetic Crosses

• Monohybrid, Dihybrid, and Polyhybrid Crosses

  • Monohybrid Cross: One trait considered.
  • Dihybrid Cross: Two traits considered, exemplifying independent assortment.
  • Polyhybrid Cross: Three or more traits considered.

• Test Cross and Back Cross

  • Test Cross: Determines genotype of an organism with a dominant trait by crossing with a homozygous recessive.
  • Back Cross: Crossing of an F1 individual with either of the parental genotypes.

Probability and Genetics

• Utilized to predict genetic outcomes.
• Rule of Multiplication: Used for independent events.
• Rule of Addition: Used for mutually exclusive events.

Unit 2: Autosomes and Sex Chromosomes

Autosomes

• First 22 pairs of human chromosomes.
• Do not determine sex but carry genetic traits.

Sex Chromosomes

• Last pair of chromosomes (XX or XY).
• Determine sex of an individual.

Sex-Linked Traits

• Traits carried on the X chromosome.
• Examples: Color blindness, hemophilia.

Unit 3: Non-Mendelian Inheritance

Types of Non-Mendelian Inheritance

• Incomplete Dominance: Offspring phenotype is a blend of parental phenotypes.
• Codominance: Both alleles are fully expressed in heterozygotes.
• Multiple Alleles and Polygenic Inheritance: Traits controlled by more than one gene.

Pedigree Analysis

• Used to track inheritance of traits in families.
• Key symbols: Squares for males, circles for females, shaded for affected individuals.

Key Takeaways

• Mendel's laws form the foundation of genetics but do not cover all inheritance cases.
• Non-Mendelian patterns provide a more complete understanding of genetic inheritance.
• Pedigree charts help visualize inheritance patterns and predict genetic conditions.

Assignments

• Review assigned tasks and refer to class calendar for submission deadlines.
• Use provided resources for further practice and clarification on topics discussed.