AP Biology Unit 7 Natural Selection

Evolution

Process by which modern organisms have descended from ancient organisms due to gradual changes over time.

Fitness

Ability of an individual to survive and reproduce

Adaptations

Characteristics that increase a chance of survival in their specific environment

Darwin’s Theory of Natural Selection (5 steps)

1. Individuals must differ-some variation is inheritable

2. Organisms produce more offspring than can survive

3. Compete for limited resources

4. Individuals best suited for their environment survive and reproduce most successfully passing their heritable traits to their offspring

5. Species alive today have descended with modification

Peppered Moths

-Sooty smoke killed the lichen on trees and darkened the bark. Dark colored moths were hard to spot because they blended in with trees. Over time, the darker moths became more common

-Later, lichen grew back making the trees lighter. Now, natural selection favors the lighter moths over generations and lighter moths are more common.

MRSA

Population of bacteria exists with variations due to random mutation. When the bacteria is treated with an antibiotic, bacteria that contain the beneficial mutation survive, others die. Resistant bacteria reproduce quickly and aren’t affected by the antibiotic.

VIST

Things that must be present for natural selection to occur

1. Variation: All life forms vary genetically within a population

2. Inheritence: Genetic traits are inherited from parents

3. Selection: Organisms with traits that are favorable get to live and pass on genes

4. Time: Evolution takes time.

Predation and Coloration

Color patterns of male guppies correspond to intensity of predation. In pools with less predators, male guppies will be brightly colored. In pools with more predators, male guppies will appear dull/drab to be less recognizable by predators.

Fossil Record

Shows the evolutionary changes that occured over time in various groups of organisms. Fossils can be dated by location, depth, and rate of isotope decay/carbon dating.

Homology

Evidence of evolution. Anatomical homologous structures represent variations that was present in their common ancestor.

Vestigial Structures

Remanents of features that served important functions in the organism’s ancestors.

ex. snake skeletons show vestiges of pelvis and leg bones from walking ancestors

Molecular Homologies

All forms of life use the same genetic code and share genes.

-ex. humans and bacteria share genes inherited from a distant common ancestor.

Biochemical and Genetic Similarities

Most precise way to compare evolution of two organisms. DNA nucleotide and protein sequences, provide evidence for evolution and ancestory.

Analogous Structures

Share similar function, but not similar ancestors. Can result from convergent evolution.

Convergent Evolution

Independent evolution of similar features in different ancestory lineages.

Mutations

Introduce new alleles in a population to increase genetic variation.

-point mutations: large scale chromosomal mutations

-sexual reproduction produces genetic diversity through crossing over, independent assortment, and random fertilization

Population

Group of individuals of the same species living at the same area at the same time

Gene Pool

Total collection of all of the alleles in a population

Population Genetics

How allele frequencies in a population change over time

HW Requirements

1. no mutations

2. large population

3. no gene flow

4. no natural selection

5. random mating

HW Equations

p²+2pq+q²=1

p+q=1

-p²: homozygous dominant

-q²: homozygous recessive

-2pq: heterozygous

-p: dominant allele frequency

-q: recessive allele frequency

Natural Selection

Survival of the fittest. When individuals with traits that help them survive and reproduce pass those traits on more often.

Genetic Drift

Random change in allele frequencies in a population

Genetic Flow

Movement of alleles between populations when individuals migrate and reproduce

Founder Effect

A few individuals in a population start a new population with a different allele frequency than the original population.

Bottleneck Effect

Sudden changes in the environment drastically reduce the size of a population, and by chance certain alleles are under or over represented among the survivors.

Diploidy

Preserves the recessive allele because it can’t be selected against unless an individual has two copies

Heterozygote Advantage

Natural selection favors heterozygous individuals where their phenotype lies between the recessive and dominant variations

Frequency-Dependent Selection

Fitness of a phenotype declines if it becomes too common

Why natural selection isn’t perfect

1. limited by existing variation, can only work with genes in the given gene pool

2. evolution is contained by history

3. adaptations are often trade-offs, a trait that is beneficial in one way may be harmful in another

4. environment is constantly changing

Speciation

Process by which a species splits into 2 or more species

Biological Species Concept

When a species is defined as a population of organisms who have the potential to interbreed in nature and produce living, fertile offspring, but are unable to reproduce with other populations of organisms.

Reproductive Isolation

The existence of biological barriers that prevent members of 2 different species from producing fertile offspring.

Prezyegotic Barriers

Prevent mating or impede fertilization.

1. temporal isolation-timing

2. Habitat isolation

3. behavioral isolation-mating calls

4. mechanical isolation-try to mate by can’t physically make it work

5. gametic isolation-gametes can’t combine

Postzygotic Barriers

Prevent a fertilized egg from developing into a fertile adult.

1. reduced hybrid viability-issues with offspring

2. reduced hybrid fertility-mating occurs, some offspring can’t reproduce

3. hybrid breakdown-issues with second generation of offspring

Allopatric Speciation

New species arises because a population is geographically isolated from it’s parent population

Sympatric Speciation

No geographic speciation, but a new species arises from a parent population.

Polyploidy

More than 2 sets of chromosomes in an organism are created as a result of nondisjunction. Leads to immediate speciation. Common in plants.

Gradualism

The proposal that species descnded from a common ancestor and gradually diverged more and more in structure and function as they acquired unique adaptations.

Punctuated Equallibrium

Long period where species remain unchanged and then are suddenly changed. Bursts and quiet periods. Rapid speciation.