Bio Exam 2 Ch 23

Do individual organisms evolve during their lifetime?

No

Natural selection may affect individuals but only what evolves?

Populations

The product of inherited genotype and environmental influences

phenotype

What part of phenotype can natural selection act on?

Only variation with genetic component

Only natural selection causes organisms to adapt to an

environment

microevolution

a change in allele frequencies in a population over generations

sexual reproduction

can shuffle existing alleles into new combinations

gene duplications

duplicated genes can take on new functions by further mutations

germ cells

cells that mutations and duplications must occur in for natural selection to occur in

discrete characters

can be classified on an either or basis, this or that, no in between

quantitative characters

vary along a continuum within a population

discontinuous variation

distinct categories, tends to be qualitative, no in between

continuous variation

no distinct variation, no limit on the value, tends to be qualitative

height, weight, heart rate, finger length, leaf length

continuous variation examples

a lot of gene and environment between 2 extremes

continuous variation is controlled by

tongue rolling, finger prints, eye color, blood groups

discontinuous variation examples

a few genes limited by the number of phenotypes with no intermediates

discontinuous variation is controlled by

Genetic variation can be measured as

Nucleotide variability and average heterozygosity

nucleotide variability

is measured by comparing the DNA sequences of pairs of individuals

average heterozygosity

is gene variability, measured as the average percent of loci that are heterozygous in a population

What is the loci % that are heterozygous

4/18=22.2 percent, divide hetero by whole

geographic variation

differences between gene pools of separate populations

cline

variation that is a graded change in a trait alone a geographic axis

population

a localized group of individuals capable of interbreeding and producing fertile offspring of the same species

gene pool

consists of all the allele for all loci in a population

fixation

if all individuals in a population are homozygous for the same allele

p+q=1

the frequencies of all alleles

Hardy Weinburg principle

frequencies of all alleles and genotypes in a population remain constant from generation to generation

If a population violates the Hardy Weinburg principle

the population is evolving and is not in equilibrium from one generation to the next

p2+2pq+q2=1

genotype frequencies

The H-W equilibrium describes a hypothetical population that is

not evolving

The five H-W conditions are

no mutations

no natural selection

no sexual selection=must have random mating

no gene flow/no migration in and out of population

extremely large population size so there is no random affects

Are the conditons of hardy weinburg met in nature?

whats this called?

rarely met

evolution

Natural populations can evolve at some loci while

being in H-W at other loci

natural selection

differential success in reproduction results in certain alleles being passed to the next generation in greater proportions

the smaller the sample

the greater the chance of random effects cause deviation from predicted result

genetic drift

in small populations allele frequencies can fluctuate (drift) unpredictability from one generation to the next

Fixation in H-W

the establishment (fixing) of one allele in the population via the loss of other alleles leading to reduced genetic variation and increased homozygosity

bottleneck effect

a sudden reduction in population size due to a change in the environment

whats the result of the bottleneck effect?

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

what happens if the bottleneck effect’s population remains small

it may be further affected by genetic drift

analogy for bottleneck effect:

Upside down bottle, big to thin

Humans can have bottleneck affect on species by

interferring with population size, number of alleles per locus

founder effect

when a few individuals become isolated from a larger population and seed a new population of heir own

allele frequencies in founder population can be different from those

in the parent population with fixation due to small population size

due to the founder effect, orginal will change frequences due to

population change and migration (violating hardy weinburg)

Effects of genetic drift

significant in small populations

causes allele frequencies to change at random

can lead to loss of genetic variation within populations\

can cause harmful alleles to become fixed

gene flow

movement of alleles among populations

gene flows via

emigration/immigration of fertile individuals or gametes

gene flow can increase or decrease the

fitness of a population depending on the environment and alleles introduced

natural selection is the only mechanism that

consistently causes adaptive evolution

new genetic variations arise by chance mutation (random) and these alleles

contribute to phenotypic variation

beneficial alleles are sorted and favored by natural selection in

enviornments

sorting

non-random

natural selection brings adaption to an environment by

acting on an organisms phenotype in that environment

are organisms perfect in their environment?

no, evolution is always occurring

reproductive success

different reproductive success via any difference that allows more offspring to be produced, mechanism of natural selection, depends on many factors

directional selection

favors individuals at one end or the other of the phenotypic range

disruptive selection

favors individuals at both extremes of the phenotypic range, average for both lines is the same.

stabilizing selection

favors intermediate variants and acts against extreme phenotypes

sexual selection

is the natural selection for mating success

sexual dimorphism

marked differences between the sexes in secondary sexual characteristics

male showiness due to a mate choice can

increase a male’s chances of attracting a female

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

how do female preferences evolve? Hypothesis suggest

a trait that is related to male health, both the male trait and female preference for that trait should increase in frequency

how does female preferences evolve by chance?

female randomly develops a preference for the good genes male and in doing so both benefit

neutral variation

genetic variation that does not confer a selective advantage or disadvantage

Mechanisms that help to preserve genetic variation

diploidy

balancing selection

diploidy

maintains genetic variation in the form of hidden recessive alleles with heterozygotes

balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population

heterozygote advantage

frequency dependent selection

heterozygote advantage

when heterozygotes have a higher fitness than do homozygotes

frequency dependent selection

fitness of a phenotyoe declines if it becomes too common in the population

what happens when a frequency becomes too popular in a population/what’s favored?

the opposite

selection can only act on existing variations because

if no new beneficial mutations occur, then there are no new variations

evolution is limited by

historical constraints

adaptions are often

a compromise

not too good, not too bad

Chance and natural selection interacts with ___ and prevents perfect organisms

the environment