Unit 11 - Evolution [Honors Biology]

evidence of evolution

1. fossils, 2. biogeography, 3. comparative anatomy (homologous/analogous structures), 4. comparative embryology, 5. molecular evidence (DNA, proteins)

fossils

the preserved remains, or traces of remains, of ancient organisms

mold fossil

a full imprint of an animal

preserved fossil

animals are preserved in amber tar or ice

trace fossil

things like footprints

cast fossil

the opposite of a mold fossil (3D fossil)

carbonized fossil

thin layer of carbon shows delicate parts of insects or plants

petrified fossil

minerals replace all or part of an organism

absolute dating

process of determining age of remains based on content and decay rate of radioactive isotopes (carbon 14, potassium)

relative dating

process of determining age of remains based on position in rock strata

law of superposition

in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest is on bottom

index fossil

widely distributed fossil, of narrow range in time, regarded as characteristic of a given geological formation [helps pinpoint age]

biogeography

geographic distribution of organisms on Earth indicates evolution in conjunction with the movement of tectonic plates over geological time

homologous structures

structurally similar features in different organisms suggesting common ancestry & divergent evolution; structures perform different functions

analogous structures

similar features found in unrelated organisms that have evolved to perform the same function; structurally dissimilar (no common ancestry); suggest convergent evolutionFeatures that serve similar functions in different species despite different evolutionary origins.

comparitive embryology

the study of similarities/differences in the development of embryos of different species; similarities in embryos are evidence of common ancestry

molecular evidence

comparing DNA sequences and protein sequencing between species to determine relatedness

molecular clock

using the number of mutations to deduce the time in prehistory when two or more life forms diverged; mutation rate is relatively constant, therefore history can be inferred

LaMarck

believed evolutionary changes were caused by organisms actively adapting themselves to environmental conditions

Law of Use and Disuse

the more an animal uses a particular structure the more prominent and well-developed the structure will become. the less a structure is used the less prominent and well-developed it will become

Inheritance of Acquired Characteristics

belief that traits an organism has developed could be passed on to offspring

Malthus

realized that populations tended to increase geometrically and limited supplies of resources could not keep up with demands of increasing population. this sets up a competitive situation.

3 major points of Darwin’s theory of Descent with Modification through Natural Selection

1. species over-reproduce

2. competition for limited resources occurs

3. variations exist among individuals making some better able to compete for limited resources than others —> those who gain the most resources reproduce more —> their offspring skew the gene pool resulting in evolution of the species

adaptation

favorable genetic variation; makes an organism more likely to survive or reproduce

fitness

measure of reproductive success; how many surviving offspring are produced

speciation

accumulation of favorable adaptations over time which results in the formation of a new species

forms of natural selection

1. genetic equilibrium

2. directional selection

3. stabilizing selection

4. disruptive selection

genetic equilibrium

condition in which allele frequencies in a population do not change from one generation to the next; rate of occurrence of traits remains constant; no evolution occuring

• disruption of genetic equilibrium => evolution

directional selection

extreme phenotype becomes a favorable adaptation; usually caused by change to environment or migration to new habitats

stabilizing selection

average phenotypes become more favorable and extreme phenotypes become more unfavorable; usually slows down the rate of evolution because of a narrowed range of variation

disruptive selection

rare form of natural selection; extreme phenotypes become more favorable than average phenotypes; creates two separate subpopulations

Hardy-Weinberg principle

outlines conditions necessary for genetic equilibrium to be maintained (NO evolution)

allelic frequency

term used to describe how often a particular allele occurs in a population

gene pool

all of the possible alleles that exist in a population

Conditions necessary to maintain genetic equilibrium (Hardy-Weinberg Principles)

1. no mutations

2. no gene flow (emigration/immigration)

3. large population [prevents genetic drift]

4. individuals mate randomly; no selective breeding

5. no natural selection (equal survivorship)

• these principles CAN NEVER BE MET —>NO GENETIC EQUILIBRIUM CAN EXIST —>evolution MUST occur

genetic drift

a change in the allelic frequency of a small population brought about by chance

founder’s effect

populations started by a few pioneering individuals moving into a new region (reduces genetic variation) —>is a random sample and don’t necessarily represent the entire population

bottleneck effect

a small group of surviving members of a population breeding together (reduces genetic variation) —>don’t represent alleles of entire population

Hardy-Weinberg formulas

p + q = 1

p² + 2pq + q² = 1

What do the letters in the Hardy-Weinberg formulas represent?

p = frequency of dominant allele

q = frequency of recessive allele

2pq = frequency of heterozygous genotype

p² = frequency of homozygous dominant genotype

q² = frequency of homozygous recessive genotype

speciation

disruption of genetic equilibrium may lead to evolution of an existing species but may not result in the formation of new species —> has to occur over many generations and requires isolation of subpopulations

Types of Isolation

Geographic Isolation and Reproductive Isolation

Geographic Isolation

new land/water barriers form; leads to allopatric speciation

allopatric speciation

species arise in separate settings

Reproductive Isolation

inability of formerly interbreeding organisms to mate and produce fertile offspring; results in sympatric speciation

sympatric speciation

species arise in the same setting

prezygotic

species evolve adaptations that prevent mating (never mate)

postzygotic

though species will mate, it is unsuccessful