Bio exam 4

the founder effect

a small group of individuals separate from a population and start a new population elsewhere

the founder effect example

The amish

• community in PA founded by a small group of german immigrants in 

  • keep marrying w/in their community and social isolation causing genetic mutations like dwarfism 

Bottleneck effect

A large population is suddenly reduced to a smaller group because of a natural disaster/event

bottleneck effect example

• a wildfire kills most of a deer population keeping one gene dominant, speccific coat color, for the next few generations due to reduced genetic diversity in new population

genetic drift

• change in allele frequency between generations due to RANDOM CHANCE

• lowers variation/heterozygosity → large impact on smaller populations

genetic drift example

a severe storm could kill most of the brown-eyed individuals in a small population, leaving a smaller group with a higher frequency of blue eyes, even if brown eyes were previously dominant

Gene flow - migration

opposes speciation

• movement of alleles between populations

• increases variation and heterozygosity

• decreases genetic differences between populations

gene flow example

• a deer from one herd/population mating with a deer from another herd/population

  • offspring now becomes part of new herd’s gene pool

Non-random mating

• individuals with certain traits that are heritable are more likely to mate over others

• sexually selected traits can, but not always, reduce fitness. It makes certain heritable traits more exaggerated if they increase mating likelihood

  • Intrasexual selection: direct competition among one sex for mates (male-male combat)

  • Intersexual selection: “mate-choice” one sex is choosy on who they mate with

• inbreeding

non random mating example

• sexual selection

  • female peacocks choosing males with larger tails

assortative mating

mating wtih similar phenotypes

dissortative mating

mating with different phenotypes

speciation 

the process by which one species splits into two or more 

• through the accumulation of microevolutionary changes leading to macroevolution 

Biological speciation

two populations are the same species if they can interbreed in nature and produce fertile, viable offspring

• emphasis on gene flow to maintain species viability

biological species concept example

• western and eastern meadowlark look nearly identical in appearance but have distinct calls and behaviors that keep them from interbreeding

  • reproductive isolation trait is the key that defines them as separate species

Morphological speciation

two populations that have distinguishable phenotypic characteristics are classified as different species

Morphological speciation example

• difference between sharks and dolphins

  • appears similar due to the environment but are distinctly different species based on their evolutionary history and physical structures

Phylogentic speciation 

species are groups of indivduals that share a unique common ancestor

• emphasis on evolutionary time; good for fossils, not real time

phylogentic speciation

the african elephant split into two species

• african forest elephant and african savanna elephant based on genetic and morphological evidence

ecological speciation

species is a group of organisms who share a commone lineage and fill a similar niche

• emphasis on disruptive selection

Ecological speciation example

distinction between human roundworm and pig roundworm

• appear very similar morphologically

• different species because they occupy different ecological niches and infect different hosts

another example is polar bear and grizzly bear

speciation process

1. Geographic barrier or disruptive selection creates reproductive isolation

2. Reproductive isolation allows for the accumulation of unique gentice differences in a population

3. Genetic Differences enhance reproductive isolation

allopatric speciation

physical geographic barrier reproductively isolating a population

allopatric speciation example

two isolated ponds with different environment conditions

• pond with predators- fish faced a high risk of being eaten by predators → natural selection favored individuals with a body shape that allowed them to escape quickly

• pond w/o predator- main selective pressures were different, related to long-duration of swimming → selection favored a body shape that thrived for long swimming periods

  • outcome: overtime populations in each pond diverged significantly in their morphology and when brough together, females of one fish preferred to mate w/ male fish w/ similar body type