microevolution

Do individual organisms evolve?

No, populations evolve

What does natural selection act on?

individuals

What is microevolution?

Change in allele frequencies in a population over generations.

Three main mechanisms that cause allele frequency change

natural selection, genetic drift (chance events that alter allele frequencies), and gene flow (the transfer of alleles between populations)

What causes adaptive evolution?

only natural selection

what does adaptive evolution increase?

it increases organisms adaptations to particular environment

What is Gregor mendel's work evidence of?

It is evidence of discrete heritable units (genes) that organisms transmit genes to their offspring

What is genetic variation caused by?

differences in genes or other DNA segments

What is a phenotype?

The product of inherited genotype and environmental influences

Natural selection can only act on variation with?

genetic component

Some phenotypic differences are determined by...

a single gene and can be classified on an either-or basis

Example of either-or basis

Mendel pea plant color

other phenotypic differences are determined by

the influence of two or more genes and vary along a continuum within a population

What is the coat color of a horse example of

Phenotypic variation

What is the human height example of?

Phenotypic variation

What genetic variation be measured as?

Gene variability or nucleotide variability

gene variability

average heterozygosity measures the average percent of loci that are heterozygous in a population

nucleotide variability

measured by comparing the DNA sequences of pairs of individuals

Why nucleotide variation rarely results in phenotypic variation?

• Most differences occur in non coding regions (introns) which are lying btw exons• variations that occur in coding regions (exons) rarely changethe amino acid sequence• exons are retained in mRNA after RNA processing, wherever exon or intron single variable site is enough to cause genetic variation

How does the phenotypic variation that is not caused by genetic differences occurs?

From environmental influences

Only genetically determined variation can have

evolutionary consequences

Examples of nonheritable variation

The caterpillar of moth having distinct appearances due to their diet,Walking chicken

New genes and alleles can arise by

mutation or gene duplication

Sexual reproduction can result in genetic variation by

recombining existing alleles

What is a mutation?

Change in the nucleotide sequence of DNA

only mutations in cells that produce \_____ can be passed to offspring

gametes

What is a point mutation?

a change in a single base pair in DNA

The effect of a sickle cell

Significant impact on phenotype

Mutations that alter the phenotype are often

harmful

How do harmful mutations stay hidden from selection

In recessive alleles and persist over generations

Mutations that result in a change in a phenotype are

Sometimes beneficial

Point mutations in noncoding regions generally result in

neutral variation, conferring no selective advantage or disadvantage

Mutations can be neutral due to redundancy in the genetic code:

not alter aa composition,so no effect on protein function

Chromosomal mutations that \________ are typically harmful

Delete, distrust, or rearrange many loci

Potential sources of variation

•Duplication of genes due to errors in meiosis (such as unequal crossing over)•Slippage during DNA replication•Activities of transposable elements

Duplication of small pieces of DNA increases

genome size and is usually less harmful

Duplicated genes can take on new functions by

further mutation

Mutation rates are often lower in

Prokaryotes

Short generation times allow mutations to

Accumulate rapidly

Viruses have both \--- mutation rates and \--- generation times

High mutation rates and short generation times

Why do viruses have high mutation rates and short generation times?

Since they have RNA genome, host cell lacks of RNA repair mechanisms

In organisms that reproduce sexually, most genetic variation results from

recombination of alleles

recombination of alleles can shuffle existing allels into new combinations through three mechanisms

•Crossing over (btw homologous chromosomes during meiosis)• independent assortment (homolog chromosomes and allels are distributed randomly into gametes)• fertilization (brings gametes together that have genetic background)

Genetic variation is required for a population to \------ but \-----

Evolve but does not guarantee that it will

For a population to evolve \----- must be at work

One or more factors that cause evolution

A population is:

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

Are populations always geographically isolated?

Populations are not always geographically isolated, but individuals typically only breed with members of their own population

gene pool

Consists of all the allels for all loci in a population

A locus is fixed if all individuals in a population are

homozygous for the same allele

If there are two or more allels for a locus

Diploid individuals may be either homozygous or heterozygous

The frequency of all allels in a population will always

Add up to 1

Hardy-Weinberg equation describes

the genetic makeup we expect for a population that is not evolving at a particular locus

If the observed genetic makeup of the population differs from expectations under Hardy-Weinberg

it suggests that the population may be evolving

In a population that is not evolving where \_______ , such a population is in \____

● gametes contribute to the next generation randomly● Mendelian inheritance occurs,● allele and genotype frequencies remain constant from generation to generationSuch a population is in Hardy-Weinberg equilibrium

Hardy-Weinberg equilibrium describes

the constant frequency of alleles in such a gene pool: no change

In real populations, allele and genotype frequencies change over time,such changes occur when

One or more of the conditions for Hardy - Weinberg equilibrium are not met

Conditions for Hardy-Weinberg Equilibrium

no mutations, random mating, no natural selection, extremely large population size, no gene flow

Consequence for no mutantions

The gene pool is modified if mutations occur or if entire genes are deleted or duplicated

Consequence for random mating

If individuals mate within a subset of the population , such as near neighbors or close relatives, random mixing of gametes does not occurAnd genotype frequencies change

Consequence of no natural selection

Allele frequences change when individuals with different genotypes showconsistent differences in their survival or reproductive success

Consequence of extremely large population size

In small populations, allele frequencies fluctuate by chance over time (ge-netic drift)

Consequence of no gene flow

By moving allels into or out of populations, gene flow can alter allel frequencies

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

natural selection, genetic drift, gene flow

New mutation can alter allele frequencies, but because mutation is rare so

The change from one generation to next will be very small

Nonrandom mating can affect

Frequency of homozygous and heterozygous genotypes, not allele frequency in the gene pool

Factors that affect evolution

mutation, non random mating, natural selection, gene flow, genetic drift

Natural selection is based on

Differential success in survival and reproduction

Individuals with heritable traits that better fitted environment produce

more offsprings than those with less fitted traits.

selection results in

alleles being passed to the next generation in proportions that differ from those in the present generation

an allele that confers resistance to DDT in fruit flies increased infrequency after (example of——- )

DDT was used widely in agriculture. (example of natural selection)

Natural selection can cause

adaptive evolution, a process in which traits that enhance survival or reproduction increase in frequency over time

the smaller a sample, the greater the chance of

random deviation from a predicted result

Genetic drift describes

how allele frequencies fluctuate unpredictably from one generation to the next

Genetic drift tends to reduce genetic variation

Through the random loss of allels

Certain circumstances can result in genetic drift having significantimpact on population which are

Founder effect and bottleneck

founder effect

occurs when a few individuals become isolated from a larger population

Allele frequencies in the small founder population can be \_________ from those in the larger parent population

different

Human populations in Northern Europe having blonde hair and blue eyes is an example of

Founder effect

bottle neck effect (genetic drift)

occurs when there is a drastic reduction in population size due to a sudden change in the environment such as fire, flood.

The resulting gene pool from bottleneck effect

may no longer be reflective of the original population's gene pool

If the population remains small

it may be further affected by genetic drift

Genetic drift is significant in small populations

Chance events alter allele frequency substantially in small populations

Genetic drift can cause allele frequencies to change at random

The change from year to year is not predictable

genetic drift can lead to loss of

genetic variation within populations

Genetic drift can cause harmful allels to become \_______ particularly in \____

Fixed; particularly in small populations

Gene flow

consists of the movement of alleles among populations

Alleles can be transferred through

the movement of fertile individuals or gametes (for example, pollen)

Gene flow tends to reduce

variation among populations over time

Gene flow can affect ——— to ———-

Gene flow can affect adaptation to local environments

variation in banding pattern in Lake Erie water snakes represents

adaptation to mainland and island habitats

Gene flow can increase

the fitness of a population

Gene flow is an important agent of evolutionary change in

modern human populations

result of gene flow

increased genetic variability and potential change in allele frequencies, mating is more common btw members of populations previously had very little contact

Natural selection is the only mechanism that consistenly causes

Adaptive evolution

Evolution by natural selection involves both

chance and sorting

New genetic variations arise by

chance

Beneficial alleles are ————- by natural selection

"sorted" and favored

Only natural selection consistently increases ————— that provide ————— which leads to adaptive evolution

Only natural selection consistently increases the frequencies of alleles that provide reproductive advantage which leads to adaptive evolution

Natural selection brings about adaptive evolution by acting on

an organism's phenotype

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals