Flashcard Set

AP Biology: Natural Selection and Evolution

14 cards

Evidence for evolution, selection, Hardy-Weinberg, speciation, and phylogenetics for the AP Biology exam.

1
Term
How is evolutionary fitness quantitatively measured within a population?
Definition
Fitness is measured by relative reproductive success, specifically the number of viable, fertile offspring an individual leaves to the next generation compared to other individuals in the population.
2
Term
Which type of natural selection shifts the overall makeup of the population by favoring variants at one extreme of a phenotypic distribution?
Definition
Directional selection.
3
Term
Anatomical structures in different species that share a common evolutionary origin but may perform different functions are called ___ structures.
Definition
homologous
4
Term
Why do analogous structures, such as the wings of an insect and the wings of a bird, not provide evidence of a recent common ancestor?
Definition
Analogous structures arise from convergent evolution, where unrelated organisms independently adapt to similar environmental pressures rather than inheriting the trait from a shared ancestor.
5
Term
What are the five conditions required for a population to remain in Hardy-Weinberg equilibrium?
Definition
No mutations

Random mating

No natural selection

Extremely large population size (no genetic drift)

No gene flow (no migration)
6
Term
In a population in Hardy-Weinberg equilibrium, a recessive genetic disorder affects 4% of the population. What is the frequency of heterozygous carriers in this population?
Definition
0.32 (or 32%). Since the homozygous recessive frequency (q^2) is 0.04, q = 0.2. This means p = 0.8 (1 - 0.2). Heterozygotes (2pq) = 2 * 0.8 * 0.2 = 0.32.
7
Term
In the Hardy-Weinberg equation p^2 + 2pq + q^2 = 1, what genetic metric does the term p^2 represent?
Definition
The frequency of the homozygous dominant genotype in the population.
8
Term
How does the effect of genetic drift on allele frequencies differ from the effect of gene flow?
Definition
Genetic drift changes allele frequencies purely by chance (especially in small populations), while gene flow changes allele frequencies through the physical movement of fertile individuals or gametes between populations.
9
Term
A severe reduction in population size due to a sudden environmental change (like a fire or flood) that randomly alters the gene pool is known as the ___ effect.
Definition
bottleneck
10
Term
What is the primary distinction between allopatric and sympatric speciation?
Definition
Allopatric speciation occurs when populations are geographically isolated from one another, whereas sympatric speciation occurs within the same geographic area, often due to polyploidy, habitat differentiation, or sexual selection.
11
Term
On a phylogenetic tree, what biological concept is represented by a node (branch point)?
Definition
A node represents the most recent common ancestor of the evolutionary lineages that split from that point.
12
Term
Define a clade (or a monophyletic group) in cladistics.
Definition
A group of organisms that includes a single ancestral species and all of its descendants.
13
Term
Describe the visual layout of a phylogenetic tree showing Species A and Species B as sister taxa, with Species C as their closest outgroup.
Definition
A single ancestral line splits at a node into two branches: one branch leads directly to Species C (the outgroup), and the other branch continues forward before splitting at a more recent node into two parallel terminal branches for Species A and Species B.
14
Term
Why does the presence of highly conserved developmental genes, such as Hox genes, across diverse animal phyla support the theory of evolution?
Definition
It indicates that these genes were inherited from a very ancient common ancestor and have been strongly preserved by natural selection due to their critical role in early body-plan development.