Genetics Midterm Study Guide: Key Concepts and Principles

Chapter 2: Mitosis and Meiosis

Cell Cycle and Regulation

The cell cycle is a series of events that cells go through as they grow and divide. Regulation of the cell cycle ensures proper division and prevents uncontrolled cell proliferation.

• Phases of the Cell Cycle: G1, S, G2, and M phases, with checkpoints at G1/S and G2/M to monitor DNA integrity and cell size.

• Checkpoints: Mechanisms that halt cell cycle progression if errors or damage are detected.

Mitosis and Meiosis

• Mitosis: Process by which somatic cells divide to produce two genetically identical daughter cells.

• Meiosis: Specialized cell division producing gametes (sperm and eggs) with half the chromosome number of the parent cell, introducing genetic variation.

• Genetic Continuity: Mitosis maintains genetic continuity; meiosis ensures continuity across generations and introduces variation.

Gametogenesis

• Spermatogenesis: Formation of sperm cells.

• Oogenesis: Formation of egg cells.

Chapters 1 and 3: Mendelian Genetics

Principles of Mendelian Genetics

• Key Terms: Gene, allele, genotype, phenotype, homozygous, heterozygous.

• Mendel's Laws: Law of Segregation and Law of Independent Assortment.

• Historical Context: Mendel's work laid the foundation for modern genetics, leading to the discovery of DNA as the genetic material.

Genetic Crosses and Analysis

• Punnett Squares: Tools for predicting genotypic and phenotypic ratios.

• Testcross: Used to determine the genotype of an individual with a dominant phenotype.

• Monohybrid, Dihybrid, Trihybrid Crosses: Used to analyze inheritance patterns of one, two, or three traits, respectively.

• Chromosomal Theory of Inheritance: Genes are located on chromosomes, which segregate and assort independently during meiosis.

• Probability in Genetics: Product and sum rules are used to calculate the likelihood of genetic outcomes.

Pedigree Analysis

• Pedigrees: Diagrams that show inheritance patterns across generations, useful for studying human genetics.

Chapter 4: Extensions of Mendelian Genetics

Non-Mendelian Inheritance

• Multiple Alleles: More than two alleles exist for a gene (e.g., ABO blood groups).

• Incomplete Dominance: Heterozygote phenotype is intermediate between homozygotes.

• Codominance: Both alleles are expressed in the phenotype (e.g., AB blood type).

• Lethal Alleles: Cause death when present in certain genotypes.

• Pleiotropy: One gene affects multiple traits.

• Gene Interactions: Epistasis occurs when one gene masks the effect of another.

• Penetrance and Expressivity: Penetrance is the proportion of individuals showing a phenotype; expressivity is the degree to which a trait is expressed.

Chapter 9: Extranuclear Inheritance

Organelle Genetics

• Chloroplast and Mitochondrial DNA: Inheritance is typically maternal; mutations can cause diseases.

• Endosymbiotic Theory: Mitochondria and chloroplasts originated from free-living bacteria.

• Human Health: Mitochondrial dysfunction is linked to aging and disease.

Chapter 5: Chromosome Mapping in Eukaryotes

Genetic Mapping

• Linkage: Genes located close together on the same chromosome tend to be inherited together.

• Recombination Frequency: Used to estimate distances between genes; 1% recombination = 1 map unit (centimorgan).

• Gene Mapping: Multiple crossovers and interference can affect mapping accuracy.

Chapter 7: Sex Determination and Sex Chromosomes

Sex Chromosome Systems

• XY System: Males are XY, females are XX (e.g., humans).

• X and Y Chromosomes: Carry genes for sex determination and other traits.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to aneuploidy (e.g., Turner syndrome, Klinefelter syndrome).

• Lyon Hypothesis: One X chromosome in females is inactivated (Barr body formation).

Chapter 8: Chromosome Mutations

Chromosomal Variations

• Aneuploidy: Abnormal number of chromosomes (e.g., trisomy 21 causes Down syndrome).

• Polyploidy: More than two sets of chromosomes.

• Structural Changes: Deletions, duplications, inversions, and translocations can alter chromosome structure and function.

Chapter 6 and Section 12.1: Bacterial and Phage Genetics, CRISPR

Bacterial Genetics

• Genetic Variation: Arises from mutation, conjugation, transformation, and transduction.

• Bacterial Growth Curve: Lag, log, stationary, and death phases.

• Plasmids: Small, circular DNA molecules that can carry antibiotic resistance genes.

• Chromosome Mapping: Interrupted mating experiments can map bacterial genes.

Phage Genetics and CRISPR

• Bacteriophages: Viruses that infect bacteria; can undergo lytic or lysogenic cycles.

• CRISPR-Cas System: Adaptive immune system in bacteria; used as a genome editing tool in biotechnology.

• Applications: CRISPR-Cas9 enables targeted gene editing in various organisms.

Midterm Essay Topics

• Mitosis vs. meiosis

• Phases of the cell cycle

• Spermatogenesis and oogenesis

• Gregor Mendel's foundational work

• Mendel's postulates

• Complementation

• Codominance

• Penetrance and expressivity

• Mitochondrial inheritance

• Extranuclear inheritance

• The Lyon hypothesis

• Mapping of genes

• Monosomies

• Nondisjunction in meiosis I vs. meiosis II

• Down syndrome birth and maternal age

• Horizontal gene transfer

• Virulent phage vs. temperate phage

Additional info: These topics cover foundational and advanced concepts in genetics, including classical Mendelian genetics, chromosome structure and function, gene mapping, bacterial and phage genetics, and modern genome editing technologies.