Evolution ch. 20-22

 

Ch 20

 

Genes within populations

 

            “Gene variation is the raw material for evolution”

I.                   Darwin

a.      Evolution:  darwom proposed descent with modification rather than the term evolution (change over time)

b.      Natural selection:  Darwin 1st to say this is how evolution occurs, some individuals with certain inherited traits produce more surviving offspring than others w/o.

c.       Lamarck:  inheritance of acquired characteristics.

                                                              i.      Darwin concluded variation was due to inherited pre existing characteristics not due to experiences.

d.      Genetic change within a population can be due to:

                                                              i.      Natural selection

                                                           ii.      Repeated mutations

                                                         iii.      Migration

                                                         iv.      Random chance event

II.               Gene variation in nature

a.      Polymorphism: more than one allele at frequencies greater than 5%

b.      Heterozygosity:  probability that an individual is heterozygous for a particular trait.

                                                              i.      Polymorphism and heterozygosity create high levels of genetic variability

c.       DNA sequence polymorphism

                                                              i.      By looking at DNA sequence we’ve found differences in sequence that don’t result in change in enzyme (variation occurs in the coding and noncoding regions of DNA)

 

Hardy Weinberg Principle

I.                   population genetics:  gene dynamics within population

II.               Mendel revisited:

a.      H/W used mendels work to determine how gene frequencies change

b.      H/W principle:  proportion of genes in a population will stay same iff:

                                                              i.      The population is very large

                                                           ii.      Random mating

                                                         iii.      No mutations occur

                                                         iv.      No immigration

                                                            v.      No selection

c.       Allele frequencies:

                                                              i.      (p+q)2= p2 + 2pq + q2

                                                           ii.      p=B ; q=b 

 

 

 

 

 

 

 

d.      why do frequencys change:

                                                              i.      mutation

                                                           ii.      gene flow

                                                         iii.      nonrandom mating (inbreeding)

                                                         iv.      genetic drift (statistical accidents in very small populations)

                                                            v.      selection

mutation:  occurs very slowly so not responsible for changing gene frequency merely raw material for variation.

 

Gene flow:  exchange of individuals amongst populations.  Effects h/w.  can bring alleles back into population that were removed by selection.

 

Non random mating:  mating between realative.  Increases homozygosity.  Doesn’t change frequency of alleles-just proportion of homo’s

 

Genetic drift:  change by chance alone.

a.      founder effect:  few individuals isolate (move etc) and pioneer a new population.  Limited raw material.  (likely found in hawaiin, Galapagos islands)

b.      bottleneck effect:  sudden reduction in population size, leaving few survivors to repopulate.  (natural disaster)

c.       selection: 

a.      natural vs artificial: environmental selection vs. breeder selection

b.      3 conditions:

                                                                                                                          i.      variation must exist

                                                                                                                       ii.      variation results in differential survival of offspring

                                                                                                                     iii.      variation must be genetic

c.       3 reasons:

                                                                                                                          i.      selection to avoid predation:  camouflage

                                                                                                                       ii.      selection due to climatic conditions:  enzymatic temperature requirements

1.      fish found at different latitudes have different allele frequencies of a particular enzyme

a.      one allele functions better in cold temp so found in greater frequency north.

                                                                                                                     iii.      Selection due to pesticide resistance

III.            maintaining polymorphism

a.      adaptive selection:  many changes in the natural environment pulling gene frequencies in either directionà maintaining polymorphism

b.      neutral theory

                                                              i.      kimura:  if population size is significantly small & mutation rate is significantly greatà maintaining polymorphism (mathamtically derived)  mutations are neutral or non deleterious.

IV.             heterozygote advantage

a.      maintains variation because heterozygotes are selected for.

b.      Sickle cell anemia: 

                                                              i.      Hemoglobin clumps together  due to nonpolar valine replacing polar glutamic acid.

                                                           ii.      SS=often fatal, NN= normal blood cell, no resistant to malaria, SN=2%abnormal hb, 98%normal hb, resistant to malaria

V.                Forms of selection:

a.      Disruptive:  favors two extreme ends of phenotypes

b.      Directional selection:  favors one extreme of phenotypes

c.       Stabilizing selection:  favors midrange phenotype

d.     

 

 

 

 

 

 

 

 

 

 

Fitness is the measure of reproductive success:  # of surviving offspring.

Selection is most powerful of the 5 agents of genetic change:

            1.Epistasis and 2.pleitropy limit selection

1.      epistasis  alleles effect expression of genes

2.      pleiotropy allele affects phenotype in different ways.

Selection acts on phenotype not genotype.

 

 

Ch 21

 

FOSSIL EVIDENCE

NATURAL SELECTION à EVOLUTION

EVIDENCES FOR EVOLUTION

DARWINS CONS

 

I.                   FOSSIL EVIDENCE

a.      Dating fossils:

                                                              i.      Early dating by  strata location (lower level=older)

                                                           ii.      Modern dating by absolute dating measuring radioactive isotope decay.

b.      Fossil evidence trends

                                                              i.      Trends are present but cannot be counted on

                                                           ii.      Horse evolution:  shows a trend toward larger body size, toe reduction, tooth size and shapà but did not follow trend completely.

1.      (Eqqus-larger than ancestor; nannipuus-smaller)

II.               NATURAL SELECTION à EVOLUTION

a.      Darwins finch beak:  31 specimens of finches è13 species from 3 islands.

                                                              i.      Gould recognized

1.      ground finches èseeds

2.      fruit eaters

3.      cactus eaters

4.      vampire

5.      tool users:  woodpecker finch uses twig etc. to poke into branches/grubs

                                                           ii.      patterns of dry years determined fittest beak type based upon food available.

1.      dry seasonsè few small/mostly large seeds

2.      weet seasons è many small seeds plentiful.

 

b.      peppermoth

                                                              i.      melanism favored p industrialization

                                                           ii.      pollution regulations forced cleanupè selection against melanism

 

III.            Artificial selection:

a.      Drosophila:  selection for abdominal bristles increased throughout generations

b.      Agriculture

c.       Domistication

 

IV.             Other evidence

a.      Anatomical record:

                                                              i.      Homologous structures:  different function common ancestor.

                                                           ii.      Analogous structures:  same function different origin

b.      DEVELOPMENT:  embryological development comparisons

c.       Vestigial structures:  no apparent function , similar to other organisms.

                                                              i.      Appendix

                                                           ii.      Manatee fingernails on fins

                                                         iii.      Baleen whale pelivic bones

                                                         iv.      Boa hip bones

V.                forms of evolution

a.      convergent: 

b.      divergent:

c.       parallel:

chapter 22

 

I.                   origin of species

a.      species defined

b.      isolating mechanisms

                                                              i.      prezygotic

1.      ecological isolation

2.      behavior isolation

3.      temporal isolation

4.      mechanical isolation

                                                           ii.      postzygotic

1.      hybrids are less fit, develop abnormally, non fertile

c.       geographic speciation

                                                              i.      allopatric speciation:  geographically isolated speciation

                                                           ii.      sympatric speciation