Genetics Midterm Cheat Sheet
CHAPTER 3: Basic Principles of Heredity
Key Terms:
- Gene: DNA sequence controlling a trait
- Allele: Variant of a gene
- Locus: Location on chromosome
- Genotype: Genetic makeup (e.g. Aa)
- Phenotype: Physical trait
- Homozygous: Two identical alleles
- Heterozygous: Two different alleles
Mendel's Laws:
- Segregation: Alleles separate during gamete formation
- Independent Assortment: Genes on different chromosomes assort independently
Cross Ratios:
- Monohybrid (Aa Aa): Genotypic 1:2:1 | Phenotypic 3:1
- Dihybrid (AaBb AaBb): 9:3:3:1
Probability Rules:
- Multiplication Rule: "and" = multiply
- Addition Rule: "or" = add
Chi-Square:
- chi^2 = ((OE)/E); p > 0.05 = accept null
CHAPTER 4: Extensions & Modifications
Dominance Types:
- Complete: Dominant masks recessive
- Incomplete: Intermediate (Red White = Pink)
- Codominance: Both alleles expressed (MN blood)
Multiple Alleles:
- ABO blood types: I, I = codominant, i = recessive
Lethal Alleles:
- 2:1 ratio suggests lethality (e.g. YY = dead)
Epistasis:
- Recessive: 9:3:4 (Labradors)
- Dominant: 12:3:1 (Squash)
