Key Concepts in Genetics and Evolution

Mendelian Monohybrid Cross

Solve using one gene (Aa × Aa), predict genotype and phenotype ratios

Mendelian Dihybrid Cross

Solve using two independent genes (AaBb × AaBb)

Incomplete Dominance

Heterozygous phenotype is a blend (e.g. red + white = pink)

Codominance

Both alleles expressed fully (e.g. Roan coat in cattle)

Multiple Alleles

More than two allele options (e.g. blood type IA, IB, i)

Polygenic Traits

Trait controlled by multiple genes (e.g. height)

Diploid vs Haploid

Diploid (2n = 46), Haploid (n = 23) - result of meiosis

Meiosis

Two divisions reducing 46 chromosomes to four 23‑chromosome gametes

Crossing Over

Figure 12‑20: homologous chromosomes exchange segments in Prophase I

Gene Linkage

Genes close together on chromosome tend to be inherited together

Griffith's Experiment (1928)

S‑strain and R‑strain bacteria evidence 'transforming principle'

Avery-MacLeod-McCarty (1944)

DNA identified as the molecule responsible for transformation

Hershey-Chase (1952)

Bacteriophage labeling confirms DNA is genetic material

Structure of Nucleotide

Sugar (deoxy‑ or ribose) + phosphate + nitrogen base

Chargaff's Rules

A=T, G=C; base percentages equal in complementary pairs

DNA Double Helix

Built on complementary base-pairing (A-T, G-C)

Telomeres

Protective ends of eukaryotic chromosomes

DNA Replication

Semiconservative process using polymerase, helicase, ligase

Replication Fork and Enzymes

Helicase unwinds; primase adds primer; polymerase synthesizes; ligase seals gaps

Origin of Replication

Single origin in prokaryotes, multiple in eukaryotes

Bacteriophage Structure

Figure 13‑2: protein head, tail, DNA injection into bacteria

Transformation

Bacteria uptake foreign DNA; basis of genetic engineering

RNA vs DNA

RNA: ribose + uracil + single-strand; DNA: deoxyribose + thymine + double-strand

mRNA, rRNA, tRNA

Three functional types in protein synthesis

Transcription

RNA polymerase reads DNA to synthesize RNA; promoter/terminator regulate transcription

Introns vs Exons

Introns removed; exons spliced during mRNA processing

Translation

mRNA codons pair with tRNA anticodons; ribosome links amino acids

Codon and Anticodon

Triplet codes in mRNA and complementary triplets in tRNA

Peptide Bond

Joins amino acids in protein synthesis

Lac Operon

Figure 14‑10: repressor binds operator until lactose inactivates it, allowing gene expression

Genome vs Karyotype

Genome = all DNA; karyotype = visual map of chromosomes

Autosomes vs Sex Chromosomes

Autosomes = chromosomes 1-22; Sex = X and Y

Sex‑linked Genes

Inherited via X or Y chromosome (e.g. colorblindness)

Pedigree Charts

Females = circles; Males = squares; show inheritance and genotype prediction

Nondisjunction

Chromosome mis-segregation (e.g. Down syndrome)

Blood Group Genetics

Alleles IA, IB, i; IAIB = AB; IAi/IAIA = A; IBi/IBIB = B; ii = O

Genetic Disorders

Sickle cell, cystic fibrosis, Huntington's—know inheritance patterns

Gel Electrophoresis

DNA fragments separated by size; smaller fragments move farther

Restriction Enzymes

Cut DNA at specific sequences

DNA Ligase

Joins DNA fragments in genetic engineering

Bt Protein

Insecticidal protein in GMO plants

Biotechnology in Bacteria

Plasmid insertion; restriction enzymes + ligase used

Selective Breeding

Humans choose traits via artificial selection

Charles Darwin

Theories: natural selection; survival of the fittest

Artificial vs Natural Selection

Humans vs environment selects traits

Fossil Evidence

Supports evolution; used by Darwin for theory

Evolution

Change in allele frequencies over time in populations

Gene Pool & Allele Frequency

Definitions and measurement in population genetics

Hardy‑Weinberg Equation

p² + 2pq + q² = 1; equilibrium model of allele/genotype frequencies

Genetic Drift

Random allele frequency changes in small populations

Gene Flow

Allele movement between populations

Directional Selection

Shifts phenotype toward one extreme

Stabilizing Selection

Favors intermediate trait values

Disruptive Selection

Favors extremes, eliminates intermediates

Speciation

New species form when populations diverge reproductively

Taxonomy

System for organizing and naming organisms

Binomial Nomenclature

Genus (capitalized) + species (lowercase), italicized

8 Levels of Classification

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Domain System

Bacteria, Archaea, Eukarya

Phylogeny

Evolutionary history as shown by cladograms

Clade

Group including a common ancestor + all descendants

Derived Characteristic

New evolutionary trait in a lineage (e.g. feathers)

Molecular Clock

Estimates divergence times based on mutation rates