Genetic study guide

Genetics Study Guide

1. Key Concepts
Genes and Alleles:
- Gene: Segment of DNA coding for a trait
- Allele: Different versions of a gene (A or a)
- Dominant allele: Masks recessive allele (A)
- Recessive allele: Expressed only when homozygous (a)
- Homozygous: Same alleles (AA or aa)
- Heterozygous: Different alleles (Aa)

Genotype vs Phenotype:
- Genotype: Genetic makeup (AA, Aa, aa)
- Phenotype: Observable trait (e.g., brown eyes)


2. Mendelian Genetics
Mendel's Laws:
1. Law of Segregation: Alleles separate during gamete formation
2. Law of Independent Assortment: Genes for different traits segregate independently

Monohybrid Cross:
- Example: Aa x Aa -> Genotypes 1 AA : 2 Aa : 1 aa; Phenotypes 3:1

Dihybrid Cross:
- Example: AaBb x AaBb -> Phenotypes 9:3:3:1


3. Non-Mendelian Genetics
Incomplete dominance: Heterozygote = blend (Red x White -> Pink)
Codominance: Both alleles expressed (AB blood type)
Multiple alleles: >2 alleles exist for a gene (ABO blood)
Polygenic inheritance: Trait controlled by multiple genes (skin color, height)
Sex-linked traits: Genes on X/Y chromosome (hemophilia, color blindness)


4. DNA and Protein
DNA Structure:
- Double helix of nucleotides (A-T, G-C)
- Composed of sugar, phosphate, nitrogenous base

DNA Replication:
- Semi-conservative
- Key enzymes: Helicase, DNA polymerase