Genetics & Evolution

🏥 Genetics Evolution

Part 1 of 7 — Mendelian Genetics

Mendels laws: segregation (alleles separate in meiosis) and independent assortment (genes on different chromosomes).

Dominant/recessive: heterozygote shows dominant phenotype; homozygous recessive shows recessive.

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Key Insight: Punnett squares: predict offspring ratios; monohybrid cross Aa x Aa = 1:2:1 genotype, 3:1 phenotype.

MCAT Tip: Test cross: cross with homozygous recessive to determine unknown genotype.

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Non-Mendelian Inheritance

Part 2 of 7 — Non-Mendelian Inheritance

Incomplete dominance: heterozygote is intermediate (red x white = pink).

Codominance: both alleles fully expressed (AB blood type).

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Key Insight: X-linked: gene on X chromosome; males are hemizygous (one copy determines phenotype).

MCAT Tip: Polygenic traits: multiple genes contribute (height, skin color); continuous distribution.

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Population Genetics

Part 3 of 7 — Population Genetics

Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1; p + q = 1 (allele frequencies).

Conditions: no mutation, no selection, no migration, random mating, large population.

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Key Insight: Genetic drift: random changes in allele frequency, stronger in small populations.

MCAT Tip: Bottleneck effect and founder effect: reduce genetic diversity.

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Natural Selection

Part 4 of 7 — Natural Selection

Natural selection: differential reproductive success based on heritable traits.

Fitness: reproductive success, not physical strength.

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Key Insight: Directional, stabilizing, and disruptive selection — different effects on trait distribution.

MCAT Tip: Sexual selection: traits favored in mate choice (peacock tail) vs survival.

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Speciation & Phylogeny

Part 5 of 7 — Speciation & Phylogeny

Speciation: formation of new species via reproductive isolation.

Allopatric: geographic barrier; Sympatric: same location, different niches or timing.

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Key Insight: Phylogenetic trees: show evolutionary relationships; most recent common ancestor at branch point.

MCAT Tip: Homologous structures: shared ancestry; Analogous: similar function, different origin (convergent evolution).

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Immune System

Part 6 of 7 — Immune System

Innate immunity: skin, mucous membranes, phagocytes, complement, inflammation — fast, nonspecific.

Adaptive immunity: B cells (antibodies, humoral) and T cells (cell-mediated) — slow, specific, memory.

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Key Insight: MHC I: on all nucleated cells, presents to CD8+ cytotoxic T cells.

MCAT Tip: MHC II: on antigen-presenting cells (macrophages, dendritic cells, B cells), presents to CD4+ helper T cells.

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Review & MCAT Practice

Part 7 of 7 — Review & MCAT Practice

Innate immunity: skin, mucous membranes, phagocytes, complement, inflammation — fast, nonspecific.

Adaptive immunity: B cells (antibodies, humoral) and T cells (cell-mediated) — slow, specific, memory.

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Key Insight: MHC I: on all nucleated cells, presents to CD8+ cytotoxic T cells.

MCAT Tip: MHC II: on antigen-presenting cells (macrophages, dendritic cells, B cells), presents to CD4+ helper T cells.

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