POPULATION GENETICS as a means to explore EVOLUTION CHARLES DARWIN (1809-1882) ALFRED WALLACE...
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Transcript of POPULATION GENETICS as a means to explore EVOLUTION CHARLES DARWIN (1809-1882) ALFRED WALLACE...
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