7: Natural Selection (AP bio)

Evolution

Change in genetic makeup of a population over time

Natural Selection

Mechanism of evolution

Components: variation, inheritance, reproductive advantage, time, evolution and adaptation

Fitness

Better adapted to environment, measured by the ability to survive and reproduce in a particular environment

Selective Pressure

Environment conditions, biotic and abiotic, allows some organisms to survive and others to not

Convergent Evolution

Process by which 2 species independently develop similar traits under similar selective pressure (e.g. sharks and dolphins)

Stabilizing selection:

Natural Selection pattern

Acts against extremeness, favors intermediate phenotype (e.g. human birth weight)

Directional Selection

Leads to a change in a trait over time, favors extremes of traits

Disruptive Selection

Favors extremes and against intermediate phenotype (e.g. apple maggot flies: 1 feeds on apples and the other feeds on apples)

Artificial Selection

Process by which humans select for traits (e.g. dog breeding)

Sexual Selection

Promotes traits that increase individual’s ability to find and attract mates

Somatic Cell Mutations

Body’s tissue, not passed down, nonreproductive cells

Germine Mutations

Passed down, good for evolution, most are neutral (mutations in noncoding genes)

Population Genetics

differences and variation, patterns

gene pool

all alleles present in all individuals of a species (e.g. eye color)

Allele frequency

# of allele in population / total # of alleles of that gene

Genotype frequency

number of individuals with genotype / total of number of individuals

Genetic Drift

random change in allele frequency to generation to generation

Bottleneck effect

large population is reduced (natural disasters, humans, alleles are lost, decrease genetic diversity)

Founder Effect

few individuals establish new population

Allele frequency is different than ancestry but caused by colonization

Nonrandom mating

individuals choose mates according to genotypes

Affects genotypes

e.g. inbreeding

Homologous structures

similar structures based on shared ancestry

Common among life

Ability to grow and respond, harness energy, and maintain homeostasis. Cell strcutre: membrane, cytoplasm, ribosome, DNA

Cellular processes

Molecular clock

uses a constant mutations rate to determine time of divergences of 2 species

vestigial structure

traits that used to be useful and functional but are no longer and are reduced in size or function

eg apendex in humans

radioactive dating

isotopes decay at a known rate, they can measure when mineral forms

compares unstable isotopes to stable daughter isotope amounts

eg carbon-14 to date wood and bones, it decays when body died

isotopes have a specific half life

biogeography

distribution of organisms on Earth

endemic species

only found in 1 place

invasive species

non-native species that spread rapidly in the absence of checks on population growth

species

a group of organisms that can potentially breed and mate with 1 another to produce viable, fertile offspring

speciation

formation of new species results from reproductive isolation

prezygotic factors

act before fertilization to prevent it

postzygotic factors

after fertilization, prevents egg from developing into fertile individual (mule)

isolated species

ecological isolation

separation of land, organisms cant meet

temporal isolation

reproduction at different times so organisms don’t cross path once its time

behavioral isolation

only mate based in songs/dances, ritualistic behaviors

mechanical isolation

they dont fit physically (genitalia)

gamete isolation

gametes dont meet

hybrid inviability

Tigers and leopards = stillbirth or miscarriage

hybrid sterility

sterile offspring

allopatric speciation

organisms of a descendant species after a period of physical separation

sympatic speciation

organisms from same ancestral species become reproductively isolated and diverge without physical separation

Adaptive radiation

rapid evolution of many new species that possess adaptations that allow them to fill previously empty ecological roles or niches

gradualism

evolution as a slow but process in which organisms change and develop slowly over time

punctuated equilibrium

evolution as a long periods of no evolutionary change followed by rapid periods of change

phylogenetic tree

visual representation of the evolutionary history of organisms over time

root

common ancestor

taxa/taxons

descendents

tips of phylogenetic tree

node

common ancestor where tree diverges into 2 species

tetrapod

4 legged

parsimony

Simplest explanation is most likely

more likely to evolve once not twice

cladograms

visual representation of the evolutionary history of organisms

monophyletic groul (clade)

common ancestor and ALL its descendants

polyphyletic groups

does not have common ancestor

paraphyletic group

common ancestors and some descendants

characters

anatomical, physiological, or molecular features

can be present or absent

shared characters

character in 2 or more groups

present in common ancestor and retained or convergent evolution

convergent evolution

2 organisms evolve independently

shared derived characters

trait evolved in the lineage leading to clade

outgroup

most distantly related taxa (group)

RNA world

can act as enzyme for reactions, stores info, replicate, evolve, key for life