POPULATION GENETICS as a means to exploreEVOLUTION

CHARLES DARWIN(1809-1882)

ALFRED WALLACE(1823-1913)

A. Theory of Evolution Around world, many people held view that

each species came about by divine (godly) creation Buddhism: 1. who cares?; 2. spiritual beings take

many forms including man in each cycle Hinduism: 1. primal man Purusa sacrificed to

become universe - head became heavens, arms became warriors, legs the commoners, feet the serfs; 2. Vishnu commanded servant Brahma to create world which he did out of lotus flower

Islam: Allah (God) created heaven and earth in 6 days (Quran 7:54)

Judeo-Christian: God created each creature including man in 6 days (Genesis I:20-25)

During 19th century, many fossils discovered of species not currently in existence Question of origin spawned many

hypotheses 1831 voyage of amateur naturalist

Charles Darwin along with 1854 exploration of naturalist Alfred Wallace gave enough evidence for both to propose theory of evolution of populations of organisms via natural selection

Poor Mr. Wallace

Darwin’s Finch Evolution

B. Natural Selection

Process that results in survival and propagation of organisms with favorable mutations that are better suited to adapt to environment than those without

Nature selects adaptations of organisms best suited to succeed in environment (“survival of the fittest”) Acts on phenotype of individual –

whatever physical appearance or expression of trait to help it to survive and reproduce (homozygous or heterozygous genotype is not important)

Best phenotype of population will dominate

Beneficial

Mutation

Detrimental Mutation

No longer referred to as “mutations” but rather “adaptations”

Mutations will always happen. Some are good, some are bad, most are neutral.

Two types of adaptations: Structural – physical changes in

appearance Physiological – change in how

organism functions or metabolizes (making venom, digesting cow milk)

Structural Adaptations

Thorns made it harder for predators to eat rosebuds

White coat helps it blend in, making it easier to stalk prey

Pouch enables joey to be protected but lets mom still roam around to find food

Opposable thumbs makes it easier to grasp small objects with one hand while leaving other hand free for defense.

.

Structural Adaptations

Evidence of natural selection is of peppered moths in industrial age England via “industrial melanism” Prior to industrial revolution, 98% of peppered moths

were light colored to blend in with light colored tree bark

typica

98%

2%

After industry & soot from factories turned tree trunks black, those dark peppered moths had an advantage and soon became most common

carbonaria

98%

2%

C. Changes in Gene Pool All alleles in population are considered gene pool

Only these alleles can make new organismsEx: If mom & dad are homozygous dominant for

brown eyes, blue eyes just aren’t in your gene pool

Numerical count of alleles in specificpopulation called allelic frequency What is allelic frequency of B & b

in this gene pool?TOTAL: 14 alleles (7 pigs)B: 7/14 = 50%b: 7/14 = 50%

CHANGE in ALLELIC FREQUENCY = EVOLUTION!

G = 9/12B = 3/12

G = 17/24B = 7/24

If gene pool has large variety of alleles, it’s considered genetically diverse High biodiversity is important in health &

survival of population against:DiseaseNatural disastersLoss of habitat

Irish Potato Famine (1845-1852) is direct result of lack of genetically diverse potatoes succumbing to mold infestation

Irish Potato Famine 1845-1852

Potatoes originated from Andes Mountains in S. America – many different varieties of potatoes Only few varieties made it to Ireland,

where poor farmers would grow it as mainstay of food

“Potato blight” fungal disease of potato crops carried on ships landed in Ireland in 1844 destroying entire crops

Mass starvation, disease, emigration led to 20-25% drop in population of Ireland

How does an organism acquire diversity? Mutations!

Beneficial - improved survivalNeutral – doesn’t improve or harm survival

Lethal – would kill organism

If allele is lethal (as in t in Tay-Sachs), will only be passed down if it doesn’t affect heterozygote Tt is completely healthy, will live to

reproduce tt will die before reproducing

Exceptions are H dominant allele in Huntington’s where individual reproduces before lethality of allele manifests

A new study (2008) has found that commercial birds raised for eggs and meat are missing more than half of the genetic diversity found in native chickens, possibly increasing a vulnerability to new diseases and raising serious questions about the sustainability of the poultry industry.

Are we in danger of famine due to lack of diversity? Corn Chickens Soybeans

Many different varieties of soy, although we only grow one

Without diversity, organism is vulnerable to disease and at risk of extinction

DodoMauritania,

1681

Passenger Pigeon

N. America 1914

Golden Toad Costa Rica 1989

Hardy-Weinberg Principle To see if evolution is occurring, there must

be a change in allele frequency An equation called the Hardy-Weinberg

equation is a mathematical way to determine if change is happening p2 + 2pq +q2 = 1.0

p = numbers of dominant alleles q = numbers of recessive alleles As long as equation = 1.0, no evolution If equation 1.0, change is happening = evolution

H-W Sample Problem

Ex: Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information calculate the following: A. The percentage of butterflies in the

population that are heterozygous. B. The frequency of homozygous dominant

individuals.

Equation: p2 +2pq +q2 = 1.0; p + q = 1.0

White (recessive) = bb = 40%then bb = q2 = 0.4 q = 0.4 = 0.632 (i.e. 0.632 x 0.632 =

0.4) q = 0.63

Since p + q = 1.0, p = 1.0 - 0.63 = 0.37 p = 0.37

A. heterozygous?2pq = 2 [(0.37)(0.63)] = 0.47

B. homozygous dominant?BB = p2 or (0.37)2 = 0.14

D. Evidence for Evolution

Direct evidence for evolution (via drug-resistant bacteria & different plant species) makes it easy to see evolution exists in lower-order species

Evidence for evolution in the higher-order species (animals & humans) is more indirect:1. Fossils: bone structures are similar but act

differently2. Anatomy: looking at bones of different

species tells us certain bones do identical things

3. Embryology: species that are way different as adults (humans vs. chickens) look identical when embryos

4. Biochemistry: DNA or RNA differences between species is good comparison (chimps & humans 98% identical)

1. Fossils

Important pieces of evidence for evolution because it provides record of early life and evolutionary history Paleontologists gathered evidence

of whale’s ancestors and believe they were land-dwelling, dog-like animals

Whale still has mammalian HIP BONES!

2. Anatomy Can compare two or more different species and

see they have structural features in common which are called homologous structures

3. Embryology Evidence of same structure in embryonic stage

tells us that all have common, albeit distant, ancestor Embryo: earliest stage of growth and

development of both plants and animals All fish, reptile, bird, and mammal embryos

have tails and gill slits (no air in uterus)

4. Biochemistry

Looking at DNA and RNA of individuals and species gives us biochemical evidence for evolution look at sequence of mitochondrial DNA and RNA to see who’s related to whom

End! Quiz on this section Thursday, March 29