Overview
This lecture covers the foundational principles of Mendelian genetics, focusing on inheritance patterns, genetic terminology, and Punnett square analysis.
Mendelian Genetics Foundations
- Gregor Mendel discovered fundamental laws of inheritance using pea plants.
- Traits are controlled by pairs of alleles located on chromosomes.
- Each parent contributes one allele for each gene to their offspring.
Key Mendelian Principles
- Law of Segregation: Each individual has two alleles for each gene, but only one allele passes to the next generation.
- Law of Independent Assortment: Genes for different traits assort independently during gamete formation.
- Dominant alleles mask the effect of recessive alleles in heterozygous individuals.
Genetic Terminology and Symbols
- Homozygous means having two identical alleles for a gene (e.g., TT or tt).
- Heterozygous means having two different alleles for a gene (e.g., Tt).
- Genotype refers to the actual alleles present, while phenotype describes the observable trait.
Punnett Squares and Inheritance Patterns
- Punnett squares predict possible genotypes and phenotypes of offspring from parental crosses.
- Monohybrid crosses involve one trait; typical phenotypic ratio in F2 generation is 3:1 (dominant:recessive).
- Dihybrid crosses involve two traits; typical phenotypic ratio in F2 is 9:3:3:1.
Exceptions and Extensions to Mendel
- Some traits show incomplete dominance or codominance, leading to intermediate phenotypes.
- Genes may be linked if they are close together on the same chromosome, which affects independent assortment.
Key Terms & Definitions
- Allele — alternative form of a gene.
- Genotype — genetic makeup (alleles) of an organism.
- Phenotype — observable characteristics of an organism.
- Homozygous — two identical alleles for a gene.
- Heterozygous — two different alleles for a gene.
- Dominant — allele that expresses its trait when present.
- Recessive — allele only expressed when both alleles are the same.
Action Items / Next Steps
- Practice setting up and solving Punnett squares for monohybrid and dihybrid crosses.
- Review assigned textbook chapter on Mendelian genetics.