Study guides › B/B › Biology
Evolution & Population Genetics
Evolution is a change in allele frequencies in a population over generations. You will learn selection, the Hardy-Weinberg model and its calculations, drift and gene flow, speciation, and how to read trees and weigh evidence.
Study this chapter in PrepMed (free)
What this chapter covers
- Natural Selection & Fitness. The MCAT defines fitness precisely and asks you to recognize each mode of selection from a distribution graph.
- Hardy-Weinberg Equilibrium. Hardy-Weinberg calculations are guaranteed MCAT-style math: start from q² and work outward.
- Drift, Gene Flow & Other Forces. Five things change allele frequencies: selection, drift, gene flow, mutation, and non-random mating. Learn the signature of each.
- Speciation & Patterns of Evolution. Sort reproductive barriers into prezygotic and postzygotic, and match each speciation mode to its setting.
- Phylogenetic Trees & Evidence for Evolution. Reading a tree correctly means tracking nodes and branches, not the order of the tips.
Key points to know
- Fitness = relative reproductive success, not strength
- Populations evolve; acquired traits are not inherited
- p + q = 1 and p² + 2pq + q² = 1
- Start from q², the only frequency you can observe for a recessive trait
- Drift is random and strongest in small populations
- Bottleneck and founder effects are special cases of drift
- Prezygotic barriers prevent fertilization; postzygotic barriers reduce hybrid success
- Allopatric speciation needs a geographic barrier
Try a practice question
In evolutionary biology, which best defines fitness?
- Physical strength and size of an organism
- Relative number of viable, fertile offspring an organism contributes
- How long an individual lives
- The ability to acquire new traits during life
Show the answer
B. Fitness measures reproductive contribution to the next generation. Strength and lifespan matter only if they raise offspring number, and acquired traits are not inherited.
Common questions
What does this chapter cover?
Evolution & Population Genetics covers Natural Selection & Fitness, Hardy-Weinberg Equilibrium, Drift, Gene Flow & Other Forces, Speciation & Patterns of Evolution, Phylogenetic Trees & Evidence for Evolution.
What should I know first?
Fitness = relative reproductive success, not strength Populations evolve; acquired traits are not inherited p + q = 1 and p² + 2pq + q² = 1
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.