Microevolution (Ch 23) and Macroevolution (Ch 24)

Gene Pools A gene pool is the sum of alleles within a population A population is a localized group of organisms of the same species

Microevolution Macroevolution Changes occurring in a population Adaptations result in evolution Evolution above the species level Origin of new taxonomic groups

Hardy-Weinberg Equilibrium To assume Hardy-Weinberg equilibrium all of the following must be true: The population must be very large (no sampling error/genetic drift) There must be no mutation There must be no natural selection No migration between populations Random mating

Hardy-Weinberg Equation p=frequency of one allele (A); q=frequency of the other allele(a); p+q=1.0 p=1-q q=1-p p2 =frequency of AA genotype; 2pq=frequency of Aa genotype; q2 =frequency of aa genotype frequencies of all individuals must add to 1 (100%) p2 + 2pq + q2 = 1

Hardy Weinberg Equilibrium Population of cats n=100 16 white and 84 black bb = white B_ = black Can we figure out the allelic frequencies of individuals BB and Bb?

Using Hardy-Weinberg equation population: 100 cats 84 black, 16 white How many of each genotype? q2 (bb): 16/100 = .16 q (b): √.16 = 0.4 p (B): 1 - 0.4 = 0.6 p2=.36 2pq=.48 q2=.16 BB Bb bb

Hardy Weinberg Ex 1 If only 6% of the population displays pale eyes (recessive gene e), what is the frequency of genotype Ee in this population? q2 = 0.06 ---> q = 0.24 p + q = 1 ---> p = 0.76 Ee = 2pq = 2(0.76)(0.24) = 0.36

Hardy Weinberg Ex 2 If the statistics for people who have PKU is 1 in 10,000, what percentage of the US population carries the gene but does not exhibit the disease? q2 = 0.0001 ---> q = 0.01 p + q = 1 ---> p = 0.99 2pq = 2(0.99)(0.01) = 0.0198 or 1.98%

Genetic Drift Genetic drift is random fluctuation in allele frequency between generations.

A Genetic Bottleneck is a Form of Genetic Drift In a genetic bottleneck, allele frequency is altered due to a population crash. Once again, small bottlenecked populations = big effect.

Genetic Bottleneck – A Historical Case A severe genetic bottleneck occurred in northern elephant seals. Other animals known to be affected by genetic bottlenecks include the cheetah and both ancient and modern human populations.

Founder Effect- new habitat The South Atlantic island of Tristan da Cunha was colonized by 15 Britons in 1814, one of them carrying an allele for retinitis pigmentosum. Among their 240 descendents living on the island today, 4 are blind by the disease and 9 others are carriers.

Gene Flow genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations) seed & pollen distribution by wind & insect migration of animals

Migration (Gene Flow)

Mutations Mutation creates variation a change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)

Nonrandom Mating Inbreeding assortive mating- choosing a mate with either similarities or differences (both shift frequencies of different genotypes)

Sexual selection It’s FEMALE CHOICE, baby!

Natural Selection differential success in reproduction; climate change food source availability predators, parasites, diseases toxins only form of microevolution that adapts a population to its environment provides “fitness” increase in the population

Genetic Variation Polymorphism- 2 or more distinct forms (morphs) within a single population of organisms

Geographic Variation-cline differences in genetic structure between populations

Mutation and Sexual Recombination -random changes to DNA errors in mitosis & meiosis environmental damage -Recombination mixing of alleles new combinations= new phenotypes

Diploidy 2nd set of chromosomes hides variations in the heterozygote Balanced polymorphism heterozygote advantage (hybrid vigor; i.e., malaria/sickle-cell anemia);

In reality there is little random mating Inbreeding can occur within small or isolated populations Mate selection- choosing a mate similar to one’s self.(Homogamy)

Sickle-Cell Prevalence Selection by malaria exposure

Evolutionary Fitness Contribution an individual makes to the gene pool for the next generation. The alleles of this individual promotes the survival or reproductive success of others that share the same allele.

Modes of Selection Stabilizing Selection- favors the middle and eliminates the extremes in a population Directional Selection- natural selection or evolutionary changes in the population Disruptive Selection- favors the two extremes creating polymorphism.

Modes of Selection

Two distinct forms in the sexes of some species Sexual Dimorphism Two distinct forms in the sexes of some species

Sexual Selection

Macroevolution: the origin of new taxonomic groups Chapter 24 Speciation: the origin of new species 1- Anagenesis (linear evolution): accumulation of heritable changes 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

What is a species? Biological species concept: a population whose members have the potential to interbreed and produce viable, fertile offspring

Other Species’ Concepts Biological Species Concept Reproductive Isolation Not necessarily easy to apply Morphological Species Concept Phenotypic differences Paleontological Species Concept Fossil species Ecological Species Concept Filling of ecological niches Phylogenetic Species Concept Evolutionary lineages/genetic history

Reproductive Isolation (isolation of gene pools) Pre-zygotic barriers: impede mating between species or hinder the fertilization of the ova Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling) Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors)

Reproductive Isolation Post-zygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity) Reduced hybrid fertility (mule; horse x donkey; cannot backbreed) Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

Modes of speciation (based on how gene flow is interrupted) Allopatric: populations segregated by a geographical barrier; adaptive radiation – diversification due to habitat change (Darwin’s finches) Sympatric: reproductively isolated subpopulation in the midst of its parent population

Sympatric Speciation Polyploidy-more than 2 paired chromosomes Allopolyploidy- infertile hybrid Sexual selection- intraspecies competition

Tempo of speciation Gradualism- species diverge more and more as they adapt Punctuated Equilibrium- periods of apparent stability and then a sudden change

Evolutionary Novelties Exaptation- structures becomes better adapted for another function- bird feathers originally kept the bird warm but later were better suited for flight Heterochromy- change in the rate of evolution- foot development in salamanders Paedomorphosis- retaining some juvenile characteristics

Analogies are products of convergent evolution