BIO FINAL UNIT 2

Microevolution

A change in allele frequencies in a population over generations — what genes are possessed in a population. for a given trait driven by Natural selection

• Discrete characters

classified on an either-or basis • Purple flowers or white flowers

Quantitative characters

vary along a continuum within a population • Polygenic • Height, skin/eye color — coded by many genes leads to greater survivorship of a pop.

• Average heterozygosity

Measures the average percent of loci that are heterozygous in a population

Geographic variation

Differences between gene pools of separate populations or population subgroups — 2 pop living in different locations WILL be different

Cline

Graded change in a trait along a geographic axis

Population

localized group of individuals capable of interbreeding • and producing fertile offspring

Gene pool

Consists of all the alleles for all loci in a population • A locus is fixed — If all individuals in a population are homozygous for the same allele

The five conditions for non-evolving populations are rarely met in nature:

No mutations

Random mating

No natural selection

Extremely large population size

No gene flow

Three major factors alter allele frequencies and bring about most evolutionary change:

• Natural selection — Fitness to the environment as it affects reproductive success - most well adapted at that place and time toward the beneficial alleles

• Genetic drift — Changes in allele frequencies of small populations due to random events - losing 1 out of 10 is more catastrophic than losing 1 out of 100

• Gene flow — Introduction or loss of alleles through migration between populations

founder effect

occurs when a few individuals become isolated from a larger population • Founding a new population in a new location

bottleneck effect

Sudden reduction in population size • due to a change in the environment • resulting gene pool • may no longer be reflective of the original population’s gene pool — massive die-off

Gene flow

consists of the movement of alleles among populations • migration — mixing pop. togethor

Directional selection

favors individuals at one end of the phenotypic range

Disruptive selection

favors individuals at both extremes of the phenotypic range — fairly rare

Stabilizing selection

favors intermediate variants and acts against extreme phenotypes

Sexual selection

natural selection for mating success • can result in sexual dimorphism • marked differences between the sexes • in secondary sexual characteristics — not directly involved in mating, but are involved in winning a mate - will guide the path of adapation

Intrasexual selection

competition among individuals of one sex (often males) • for mates of the opposite sex

Intersexual selection

often called mate choice • occurs when individuals of one sex (usually females) • are choosy in selecting their mates

Diploidy

Maintains genetic variation in the form of hidden recessive alleles • heterozygosity

Balancing selection

Occurs when natural selection • maintains stable frequencies of two or more phenotypic forms in a population - 2 or more phenotypic forms

Heterozygote advantage

Occurs when heterozygotes have a higher fitness • than do both homozygotes — how you maintain a disease-hopping allele

Natural selection • Sickle-cell allele • tends to maintain two or more alleles at that locus • Causes mutations in hemoglobin

Frequency-dependent selection

The fitness of a phenotype declines • if it becomes too common in the population • Selection can favor whichever phenotype is less common in a population — so, the fishes' mouths change/mutate often to switch up and prevent the disadvantage

Speciation

Origin of new species, is at the focal point of evolutionary theory

Microevolution

consists of adaptations that evolve within a population • confined to one gene pool

Macroevolution

refers to evolutionary change above the species level • accumulation of microevolutionary changes

biological species concept

species is a group of populations • Whose members have the potential to interbreed • Produce viable, fertile offspring • Do not breed successfully with other populations

Reproductive isolation

Existence of biological factors (barriers) • Impede two species from producing viable, fertile offspring • Prezygotic vs. postzygotic — what problems to overcome before reproduction vs after reproduction

Prezygotic barriers

• - Habitat isolation

• - temporal isolation

• - behavioral isolation

• - mechanical isolation

• - gametic isolation

Postzygotic barriers

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

Reduced hybrid viability:

Genes of the different parent species may interact and impair the hybrid’s development

• Cytologic — can’t finish development

• Zygotic mortality — as soon as the egg begins to divide, it fails

Reduced hybrid fertility:

Even if hybrids are vigorous, they may be sterile

Hybrid breakdown:

Some first-generation hybrids are fertile • but mated with another species or with either parent species • offspring of the next generation are feeble or sterile — much less adaptive to the habitat or less fertile

Morphological species concept

defines a species by structural features • It applies to sexual and asexual species but relies on subjective criteria

Ecological species concept

• - not as common

• views a species in terms of its ecological niche • sexual and asexual species

• -What kinds of habitats or niches are they using, and does it affect the reproduction between these 2 species

Phylogenetic species concept

defines a species as the smallest group of individuals on a phylogenetic tree • sexual and asexual species • but it can be difficult to determine the degree of difference required for separate species

Allopatric speciation

gene flow is interrupted or reduced • when a population is divided into geographically isolated subpopulations

• there is no gene glow -

Sympatric speciation

speciation takes place in geographically overlapping populations

-because of a common ancestor

Polyploidy

Is the presence of extra sets of chromosomes • due to accidents during cell division

Autopolyploid

An individual with more than two chromosome sets • derived from one species

Allopolyploid

a species with multiple sets of chromosomes derived from different species

-an unusual circumstance that happened to work out

When closely related species meet in a hybrid zone • there are three possible outcomes:

1. Strengthening of reproductive barriers

2. Weakening of reproductive barriers

3. Continued formation of hybrid individuals

taxon

Taxonomic unit at any level of hierarchy

Sister taxa

are groups that share an immediate common ancestor

Homology

similarity due to shared ancestry

Analogy

similarity due to convergent evolution

Homoplasy

Analogous structures or molecular sequences that evolved independently

Homology

can be distinguished from analogy by comparing fossil evidence and the degree of complexity

Cladistics

grouping organisms by common descent

Clade

• A group of species that includes an ancestral species and all its descendants

• can be nested in larger clades, but not all groupings of organisms qualify as clades • A valid clade is monophyletic

• signifying that it consists of the ancestor species and all its descendants

Maximum parsimony

the tree that requires the fewest evolutionary events (appearances of shared derived characters)

Maximum likelihood

• -given certain rules about how DNA changes over time

• a tree can be found that reflects the most likely sequence of evolutionary events

Paralogous genes

• result from gene duplication

• so are found in more than one copy in the genome

• can diverge within the clade that carries them

• and often evolve new functions

Molecular clock

uses constant rates of evolution in some genes • to estimate the absolute time of evolutionary change

Neutral theory

states that much evolutionary change in genes and proteins

• does not affect fitness and therefore is not influenced by Darwinian selection

• the rate of molecular change in these genes and proteins

• should be regular like a clock

Horizontal gene transfer

movement of genes from one genome to another

• Very common in prokaryotes 4

• Viruses and eukaryotes do it too

• Complicates efforts to build a tree of life