Download Honors Biology Review Sheet: Population Evolution Definitions and

Honors Biology Review Sheet: Population Evolution
Definitions and Examples:
Speciation: the formation of a new species
Cladistics: classification of organisms based on the branching of descendant lineages
from a common ancestor.
Ingroup: a group of people sharing similar interests and attitudes, producing feelings of
solidarity, community, and exclusivity.
Outgroup: people outside one’s own group, especially as considered to be inferior or
alien; a group perceived as other than one’s own.
Primitive characters: ??
Derived characters: characteristics that appears in recent parts of a lineage, but not in
its older members.
Genetic drift: random changes in the allele frequencies of a population due to chance
happenings. This generally occurs in a small population (large populations usually are
able to withstand these events without significant effect on their allele frequencies).
Unlike natural selection, an individual’s fitness generally does not have great influence
on whether or not it is removed from the gene pool during genetic drift (it is a nonselective event). The small population is not representative of the larger “parent
population” (certain alleles may be lost, over-represented, or under-represented). There
tends to be less genetic diversity. Examples: bottleneck effect and founder effect.
Bottleneck effect: occurs when catastrophic events (volcanic eruption, earthquake, fire,
flood, over-hunting) decimate a population so that only a small percentage of the
population survives and are left to repopulate the community (or the world, in severe
instances) Examples: cheetahs and ice age, Northern Elephant Seals and over-hunting.
Founder effect: a small number of individuals from a large population migrate and
colonize a new habitat. Examples: “Mutiny on the Bounty” and Pitcairn Island, Darwin’s
finches and the Galapagos Islands.
Convergent evolution: (different populations or species evolving in similar environments)
Process by which unrelated organisms independently evolve similarities. Evolution of
similar traits in distantly related organisms. Leads to production of analogous structures.
Examples: wings of birds and butterflies, insect mimicry, streamlined shape of fish and
small whales.
Adaptive radiation: type of divergent evolution in which ancestral species develop into
an array of species, each specialized to fit into a different niche. Process by which a
species (or small group of species) rapidly evolves into several different forms.
Relatively rapid evolution of many diversely adapted species from a common ancestor.
Examples: Darwin’s finches, Hawaiian honeycreepers.
Divergent Evolution: (similar populations or species evolving in different environments)
Process in which once-related populations evolve independently (often because of
geographic isolation). Two or more related species becoming more and more dissimilar.
Evolution in which highly distinct species were once both similar to an ancestral
species. The presence of homologous structures in different species is an indication of
divergent evolution.
Examples: polar bear and brown bear, red fox and kit fox.
Coevolution: (different populations or species evolving in similar environments) Process
by which unrelated organisms independently evolve similarities. Evolution of similar
traits in distantly related organisms. Leads to production of analogous structures.
Examples: Flowers (shape, scent, or color) and their Pollinators (feeding structures of
insects, birds, bats), Predators and Prey.
Analogous Structures: structures that are similar in function but not evolutionary origin.
Gene Pool: the combined genetic material for all the members of a population. (all the
genes in a population)
Allele frequency: the number of times a specific allele occurs in a population divided by
the total number of alleles present (for a gene) in that population.
Examples: a population of 500 people each have two alleles for blood type (1000
alleles)
Alleles  there are 300 IA, 100 IB and 600 i
Allele frequency  IA = 30%, IB= 10%, i= 60%
Genetic equilibrium: a condition in which the allele frequencies of a population remain
constant from generation to generation  no evolution would be occurring.
Concepts:
Hardy-Weinberg principle: describes the specific conditions required for genetic
equilibrium to remain unchanged in a population (condition necessary for no evolution).
The conditions for the populations are: no natural selection, no migration, no mutations,
mating must be random (no preferential selection of mates), and it must be a large
population.
P= frequency of the dominant allele (A)
Q= frequency of the recessive allele (a)
P+q= 1 (100%)
This principle can also be used to predict the probability of genotypes:
P2= frequency of the homozygous dominant genotype (AA)
2pq= frequency of the heterozygous genotype (Aa)
Q2= frequency of the homozygous recessive genotype (aa)
P2+2pq+q2=1
Use of cladograms: *IN LAB PACKET*
Explain relationship between isolating mechanisms and speciation:
 Individuals of the same population interbreed and share a common gene pool.
 When two populations of the same species become reproductively isolated from
each other, they cannot interbreed. These populations start to have separate
gene pools and respond to natural selection as separate units.
 Reproductive isolation can develop in a variety of ways including the following:
Behavioral Isolation: occurs when two populations are capable of interbreeding,
but have differences in behavior, such as courtship rituals.
Examples: Eastern and Western meadowlarks use different mating songs.
Geographical Isolation: (allopatric speciation) Occurs when two populations are
separated by geographic barriers such as mountains, oceans, or rivers.
Examples: Subspecies Abert squirrel and Kaibab squirrel (separated by the
Colorado River about 10,000 years ago)
Temporal Isolation: occurs when two or more species reproduce at different
times.
Examples: Three similar species of orchids all live in the same rainforest. Each
species only releases pollen on a single day- because each species releases
pollen on a different day, they cannot pollinate one another.

Speciation is the formation of a new species.
Sources of genetic variation (mutations and gene shuffling):
Mutations: Mutations are the source of new genetic information. They can form new
alleles. May occur as a result of a mistake during replication or environmental factors
(e.g. radiation, certain chemicals). Mutations do not always affect the expressed
phenotype of the organism, but when they do they can affect the fitness of that
organism and therefore the subsequent allele frequencies of future generations.
Sexual Reproduction: Sexual reproduction is an important source of genetic variation
because it combines genetic information from two sources to produce a new
combination of genes (this does not change the relative allele frequencies of the
population, although nonrandom mating would.)
Gene Shuffling: occurs during the production of gametes. It includes crossing-over and
the independent assortment of chromosomes, both of which increase the number of
possible genotypes (formation of gametes). (analogous to shuffling a deck of cards- you
could be dealt many different hands but it does change the number (frequency) of aces,
kings, queens, ect.) (This also does not change the relative allele frequencies of the
population.)