AP Bio - Unit 7: Evolution (overall summary)

Law of Evolution

Law of Evolution

The change in the genetic allele frequency of a population over time resulting in a change in phenotypic characteristics

Allele Frequency

The incidence of gene variance

5 Mechanisms of Evolution

Natural selection, mutation, gene flow, sexual selection, and genetic drift

what is natural selection

• happens at a INDIVIDUAL LEVEL

• the adaptive trait (trait that promotes survival) persists

• 4 conditions for natural selection (VOIDs)

  • Varience: differences due to random fertilization, crossing over, and independent assortment

  • Overpopulation: more of one species means some will have to die and the adaptive trait will become more prominent

  • Inheritance: parents pass on genes

  • Differential Survival: the struggle for existence means advantageous characteristics survivethe struggle for existence means advantageous characteristics survive

Fitness

reproductive success

Selection Pressure

Force that causes a population to evolve. The stronger it is the more change there is

Mutation

a random change in DNA

Gene Flow

The transfer of genes between different populations e.g. migration

Sexual selection

The selection of a mate based on phenotypic characteristics

e.g. peacock feathers

Genetic Drift

Chance event that causes change in SMALL POPULATIONS

2 types:

• Bottleneck effect

  • Sudden disaster that happens to pick survivors with different alleles

• Founder effect

  • A few individuals from one population start a new population and therefore change the allele frequencyA few individuals from one population start a new population and therefore change the allele frequency

Evidence of Evolution

• fossil record analysis

• molecular evidence

• experiments

• observation

• comparative anatomy (homologous vs analogous)

• artificial selection (breeding)

• comparative embryology

• biogeography

types of population selection

Directional, stabilizing, and disruptive

Species

A group of living organisms consisting of similar individuals capable of interbreeding and producing fertile offspring

Hardy-Weinberg meaning and equation

Genetic variation will stay consistent across generations in the absence of disturbances

p = dominant

q = recessive

phenotypic frequency:

p² + 2pq + q² = 1

Allele Frequency:

p + q = 1

speciation

The formation of a new and distinct species in the course of evolution

2 Types of speciation

Allopatric and sympatric

Allopatric Speciaiton

One species is separated by geographic environments they undergo allopatric speciation. If they were to meet again in the future they would not interbreed

e.g. california salamanders

Sympatric Speciation

Even though both populations inhabit the same area, a new species evolves through pre-zygotic isolation

Types of pre-zygotic isolation

Gamete Isolation

• gametes cant fuse/fertilize

Behavioral Isolation

• courtship displays and different

Mechanical Isolation

• Incompatible sex organs

Temporal Isolation

• mating timing becomes different (nocturnal vs diurnal)

Habitat Isolation

• different habitats in the same location

post-Zygotic isolation

prevents the creation of a fertile offspring

Advantages of hybridization

favorable traits, survival of endangered species

Disadvantages of hybridizaiton

low zygotic viability (severe abnormalities, fails to mature), infertility, low adult viability (low survival rate because traits arent suited for any environment)

Micro evolution vs Macro evolution

micro: evolution in a short period of time (couple of generations)

macro: evolution over a long period of time

Phylogeny

The history of the evolution of a species in reference to a line of ancestry

evidence used in phylogeny (strongest to weakest)

• DNA

• Comparative anatomy

• Developmental biology

• Behavior

cladogram

phylogenic tree

shared trait

a trait shared between 2+ lineages

conserved gene

a gene remained generally unchanged throughout most of the lineage