152 ❯ STEP 4. Review the Knowledge You Need to Score High
Sources of variation within populationsare- Mutation:random changes in DNA can introduce new alleles into a population.
- Sexual reproduction:crossover, independent assortment, random gamete combination.
- Balanced polymorphism:the maintenance of two or more phenotypic variants.
Speciationis the process by which new species evolve: - Allopatric speciation:interbreeding stops because some physical barrier splits the popu-
lation into two. If two populations evolve separately and change so they cannot inter-
breed, speciation has occurred. - Sympatric speciation:interbreeding stops even though no physical barrier prevents it.
- Polyploidy:condition in which individual has higher than normal number of chro-
mosome sets. Polyploidic individuals cannot reproduce with nonpolyploidics. - Balanced polymorphism: two phenotypic variants become so different that the two
groups stop interbreeding.
Other terms to remember are
Adaptive radiation:rapid series of speciation events that occur when one or more ancestral
species invades a new environment.
Hardy-Weinberg equilibrium: p+q=1,p^2 + 2 pq+q^2 =1. Evolution is notoccurring. The
rulesfor this are no mutations, no gene flow, no genetic drift, no natural selection, and
random mating.
Homologous character:traits similar between organisms that arose from a common ancestor.
Vestigial character:character contained by organism that is no longer functionally useful
(appendix).
Gradualism:evolutionary change is a slow and steady process.
Punctuated equilibria:evolutionary change occurs in rapid bursts separated by large periods
of no change.
Heterotroph theory:theory that describes how life evolved from original heterotrophs.
Convergent character:traits similar to two or more organisms that do notshare common
ancestor; parallel evolution.
Convergent evolution:two unrelated species evolve in a way that makes them moresimilar.
Divergent evolution:two related species evolve in a way that makes them lesssimilar.
- Polyploidy:condition in which individual has higher than normal number of chro-