Overview
This lecture covers fundamental concepts in genetics, including cell division, inheritance patterns, DNA structure, errors in meiosis, reproductive technologies, and pedigree analysis.
Cell Division and Types
- Cell division enables growth, repair, replacement, and reproduction.
- Three types: binary fission (prokaryotes), mitosis (eukaryotes), meiosis (eukaryotes for gamete formation).
- Asexual reproduction creates identical offspring; sexual reproduction combines genetic material from two parents.
Cell Cycle and Cancer
- The cell cycle is the sequence of growth, DNA replication, and division, controlled by genes.
- Malfunctions in this cycle may cause uncontrolled division, leading to cancer.
Chromosomes and Genetic Material
- Chromosomes are DNA-protein complexes in the nucleus carrying genes.
- Genes are DNA segments coding for proteins; alleles are variant forms of a gene.
- Eukaryotic somatic cells are diploid (2n); gametes are haploid (n).
DNA and Base Pairing
- DNA is a double helix built from nucleotides: deoxyribose sugar, phosphate, and nitrogen base (A, T, G, C).
- Base-pairing: A-T, G-C; the sequence encodes genetic instructions.
- Mutations, such as base additions or deletions, can alter genetic outcomes.
Meiosis and Genetic Variation
- Meiosis reduces chromosome number by half, creating four unique gametes.
- Homologous chromosomes exchange genes (crossing over) during prophase I for genetic variation.
- Oogenesis (egg formation) produces one viable egg; spermatogenesis produces four sperm.
Errors in Meiosis
- Nondisjunction leads to gametes with missing or extra chromosomes (trisomy, monosomy).
- Chromosomal errors include deletions, duplications, inversions, and translocations.
- Karyotypes can detect abnormal chromosome numbers or structures.
Reproductive Strategies and Technologies
- Selective breeding enhances desirable traits in plants and animals.
- Artificial insemination and embryo transfer facilitate desirable offspring.
- IVF and PGD enable fertilization outside the body and early genetic testing.
Patterns of Inheritance
- Genotype: allele combination; phenotype: trait appearance.
- Dominant alleles mask recessive ones; homozygous: same alleles, heterozygous: different alleles.
- Punnett squares predict inheritance patterns.
- Dihybrid crosses study two traits; Law of Independent Assortment states traits are inherited independently.
Complex Inheritance Patterns
- Incomplete dominance: blended traits.
- Codominance: both alleles expressed (e.g., roan cows).
- Multiple alleles: more than two forms (e.g., blood types).
- Sex linkage: traits on sex chromosomes; X-linked traits often affect males more.
- Polygenic inheritance: many genes influence a single trait.
Pedigrees and Modes of Inheritance
- Pedigrees chart family trait inheritance across generations.
- Autosomal dominant: trait appears in every generation.
- Autosomal recessive: can skip generations; both parents must be carriers.
- Sex-linked: affects one sex more than the other.
Key Terms & Definitions
- Gene — segment of DNA coding for a protein.
- Allele — different form of a gene.
- Chromosome — DNA-protein structure carrying genetic info.
- Diploid (2n) — two sets of chromosomes.
- Haploid (n) — one set of chromosomes.
- Mitosis — cell division for growth/repair.
- Meiosis — cell division for gametes.
- Crossing over — exchange of genes between homologous chromosomes.
- Genotype — genetic makeup.
- Phenotype — observable traits.
Action Items / Next Steps
- Review diagrams of mitosis, meiosis, Punnett squares, and pedigrees.
- Practice problems involving inheritance patterns and genetic calculations.
- Read textbook sections on DNA structure and complex inheritance patterns.