WEEK 1 — Introduction & Review of Key Genetic
Principles
Jan 5, 6 & 9 | Chapters 8, 9, 10, 11, 12 + Purple Pages F-36–F-38
1.1 The Cell Cycle & Mitosis (Ch. 8)
Cell division is the basis of growth, repair, and asexual reproduction. The cell cycle has two
major phases: interphase (where the cell grows and copies its DNA) and the mitotic phase
(where the cell divides).
Phases of the Cell Cycle
• G1 (Gap 1): Cell grows, synthesizes proteins, and carries out normal metabolic
functions. Cell 'decides' whether to divide.
• S (Synthesis): DNA replication occurs — each chromosome is duplicated, producing
sister chromatids joined at the centromere.
• G2 (Gap 2): Further growth; cell prepares division machinery (tubulin for spindle fibres).
• M (Mitosis): Nuclear division — PMAT (Prophase, Metaphase, Anaphase, Telophase).
• Cytokinesis: Division of the cytoplasm (cleavage furrow in animals; cell plate in plants).
Mitosis — Step by Step
• Chromosomes condense and become visible; spindle forms; nuclear envelope
breaks down.: Prophase
• Chromosomes align along the metaphase plate; kinetochore microtubules attach.:
Metaphase
• Sister chromatids are pulled to opposite poles by shortening microtubules.:
Anaphase
• Nuclear envelopes reform around each set of chromosomes; chromosomes
decondense.: Telophase
Key Terms
Chromatin: DNA + histone proteins in an uncoiled state (during interphase).
Chromosome: Condensed, coiled chromatin; visible during mitosis.
Sister chromatids: Identical copies of a chromosome joined at the centromere after DNA
replication.
Centromere: Region of DNA where sister chromatids are most tightly joined; where kinetochore
forms.
Kinetochore: Protein complex at centromere; site of spindle microtubule attachment.
Spindle checkpoint: Ensures all chromosomes are attached before anaphase proceeds.
,1.2 Meiosis & Sexual Reproduction (Ch. 9)
Meiosis produces haploid gametes from diploid cells. It involves two successive divisions
(Meiosis I and II) but only one round of DNA replication, yielding 4 genetically unique daughter
cells.
Meiosis I vs. Meiosis II
Feature Meiosis I Meiosis II
Type of division Reductional (diploid → Equational (like mitosis)
haploid)
What separates Homologous chromosome Sister chromatids
pairs
Outcome 2 haploid cells 4 haploid cells
Crossing over Occurs during prophase I Does not occur
Sources of Genetic Variation in Meiosis
• Independent assortment: Homologous pairs orient randomly at metaphase I. 2^23
possible combinations in humans.
• Crossing over (recombination): Homologs exchange segments during prophase I at
chiasmata. Shuffles alleles.
• Random fertilization: Any egg can fuse with any sperm, multiplying genetic variation.
1.3 Mendelian Genetics & Beyond (Ch. 10–12)
Mendel's Laws
Law of Segregation: Each organism has two alleles per gene; they separate during gamete
formation so each gamete carries one allele.
Law of Independent Assortment: Genes on different chromosomes are inherited
independently of each other.
Dominance: When two different alleles are present, the dominant allele is expressed; the
recessive is masked.
Extensions to Mendel
• Incomplete dominance: Heterozygote shows intermediate phenotype (e.g., red × white =
pink).
• Codominance: Both alleles expressed simultaneously (e.g., AB blood type).
• Pleiotropy: One gene affects multiple phenotypic traits (e.g., sickle-cell anemia).
• Epistasis: One gene masks the expression of a different gene.
• Polygenic inheritance: Multiple genes contribute to a quantitative trait (e.g., skin colour,
height).
• Linkage: Genes on the same chromosome tend to be inherited together; recombination
frequency used to map gene distance.
, • Sex-linked traits: Genes on sex chromosomes; X-linked recessive traits (e.g., colour
blindness) more common in males.
Purple Pages Summary (F-36–F-38): Genetic Problem Solving
• Punnett squares for monohybrid and dihybrid crosses.
• Testcross: Cross unknown dominant phenotype with homozygous recessive to
determine genotype.
• Chi-square test: Statistical method to determine if observed ratios fit expected Mendelian
ratios.
Principles
Jan 5, 6 & 9 | Chapters 8, 9, 10, 11, 12 + Purple Pages F-36–F-38
1.1 The Cell Cycle & Mitosis (Ch. 8)
Cell division is the basis of growth, repair, and asexual reproduction. The cell cycle has two
major phases: interphase (where the cell grows and copies its DNA) and the mitotic phase
(where the cell divides).
Phases of the Cell Cycle
• G1 (Gap 1): Cell grows, synthesizes proteins, and carries out normal metabolic
functions. Cell 'decides' whether to divide.
• S (Synthesis): DNA replication occurs — each chromosome is duplicated, producing
sister chromatids joined at the centromere.
• G2 (Gap 2): Further growth; cell prepares division machinery (tubulin for spindle fibres).
• M (Mitosis): Nuclear division — PMAT (Prophase, Metaphase, Anaphase, Telophase).
• Cytokinesis: Division of the cytoplasm (cleavage furrow in animals; cell plate in plants).
Mitosis — Step by Step
• Chromosomes condense and become visible; spindle forms; nuclear envelope
breaks down.: Prophase
• Chromosomes align along the metaphase plate; kinetochore microtubules attach.:
Metaphase
• Sister chromatids are pulled to opposite poles by shortening microtubules.:
Anaphase
• Nuclear envelopes reform around each set of chromosomes; chromosomes
decondense.: Telophase
Key Terms
Chromatin: DNA + histone proteins in an uncoiled state (during interphase).
Chromosome: Condensed, coiled chromatin; visible during mitosis.
Sister chromatids: Identical copies of a chromosome joined at the centromere after DNA
replication.
Centromere: Region of DNA where sister chromatids are most tightly joined; where kinetochore
forms.
Kinetochore: Protein complex at centromere; site of spindle microtubule attachment.
Spindle checkpoint: Ensures all chromosomes are attached before anaphase proceeds.
,1.2 Meiosis & Sexual Reproduction (Ch. 9)
Meiosis produces haploid gametes from diploid cells. It involves two successive divisions
(Meiosis I and II) but only one round of DNA replication, yielding 4 genetically unique daughter
cells.
Meiosis I vs. Meiosis II
Feature Meiosis I Meiosis II
Type of division Reductional (diploid → Equational (like mitosis)
haploid)
What separates Homologous chromosome Sister chromatids
pairs
Outcome 2 haploid cells 4 haploid cells
Crossing over Occurs during prophase I Does not occur
Sources of Genetic Variation in Meiosis
• Independent assortment: Homologous pairs orient randomly at metaphase I. 2^23
possible combinations in humans.
• Crossing over (recombination): Homologs exchange segments during prophase I at
chiasmata. Shuffles alleles.
• Random fertilization: Any egg can fuse with any sperm, multiplying genetic variation.
1.3 Mendelian Genetics & Beyond (Ch. 10–12)
Mendel's Laws
Law of Segregation: Each organism has two alleles per gene; they separate during gamete
formation so each gamete carries one allele.
Law of Independent Assortment: Genes on different chromosomes are inherited
independently of each other.
Dominance: When two different alleles are present, the dominant allele is expressed; the
recessive is masked.
Extensions to Mendel
• Incomplete dominance: Heterozygote shows intermediate phenotype (e.g., red × white =
pink).
• Codominance: Both alleles expressed simultaneously (e.g., AB blood type).
• Pleiotropy: One gene affects multiple phenotypic traits (e.g., sickle-cell anemia).
• Epistasis: One gene masks the expression of a different gene.
• Polygenic inheritance: Multiple genes contribute to a quantitative trait (e.g., skin colour,
height).
• Linkage: Genes on the same chromosome tend to be inherited together; recombination
frequency used to map gene distance.
, • Sex-linked traits: Genes on sex chromosomes; X-linked recessive traits (e.g., colour
blindness) more common in males.
Purple Pages Summary (F-36–F-38): Genetic Problem Solving
• Punnett squares for monohybrid and dihybrid crosses.
• Testcross: Cross unknown dominant phenotype with homozygous recessive to
determine genotype.
• Chi-square test: Statistical method to determine if observed ratios fit expected Mendelian
ratios.
