Evolution, Part II

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Major Elements Of Life

• Carbon • Hydrogen

C H

• Oxygen

O

• Nitrogen

N

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Simple Molecules

H O H C

Chemical Evolution

O

More Complex Molecules • Carbohydrates • Fatty Acids • Amino Acids

H O H H N H H H H C H H

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Carbohydrates

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Fatty Acids

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Amino Acids

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Figure 02.12

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Proteinoid Microspheres • Similar to protocells • Protocells – Reproduce – Natural selection favored those with the most efficient replicating systems • RNA • DNA 8

Cyanobacteria

• Photosynthesis – Produce oxygen – Produce carbohydrates Carbon Dioxide + Water = Glucose + Oxygen 9

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Microevolution

• Change in allele frequency of a population – Populations evolve, individuals do not 11

Terms

• Allele – Member of a paired gene • Dominant allele – Allele that is expressed when combined with a recessive allele • Recessive allele – Allele that is NOT expressed when combined with a dominant allele • Homozygous – Both alleles the same, AA or aa • Heterozygous – Alleles are different, Aa 12

Terms

• Codominance – Both alleles are dominant, AB blood type • Gene Pool – All the alleles in a population 13

Math Explains Allele Frequencies • p + q = 1 • p = percent of dominant population alleles in a • q = percent of recessive alleles in a population • If 70% of alleles in a population are dominant then 30% must be recessive 14

Genotype Frequencies • Square the equation p + q = 1 • p 2 + 2pq + q 2 = 1 • Correlation between genotypes and variables in the equation are: • p 2 = AA • 2pq = Aa • q 2 = aa 15

Hardy-Weinberg Equations • p + q = 1 – Frequency of dominant alleles plus frequency of recessive alleles is 100% ( or 1) • p 2 + 2pq + q 2 = 1 – AA plus 2Aa plus aa add up to 100% (or 1) • Applies to populations that are not changing – They are in equilibrium 16

Hardy-Weinberg Example • Normal pigmentation (not albino) = A • Albinism recessive = a • AA = (p 2 ) = normal • Aa = (2pq) = normal • aa = (q 2 ) = Albinism • 1 in 20,000 people have albinism • aa = 1/20,000 = 0.00005

• a = 1/141 = 0.00707

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First Equation • p + q = 1 – p is the frequency of the dominant allele, A – q is the frequency of the recessive allele a • p + 0.00707 = 1 • p = 1- q = .9929

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Second Equation • p 2 + 2pq + q 2 = 1 • p 2 = AA – .9929

x .9929

= .9858

• 2pq = Aa – 2 x .9929

x 0.00707 = .0140

• q 2 = aa – .00005

• .9858 + .0140 + .00005 = 0.99985 or 1 19

Cystic Fibrosis • Cystic fibrosis affects 1 in 2000 white Americans • Cystic fibrosis is recessive = cc • 1 in 2000 = 1/2000 = .0005

• q 2 = .0005

• What is q?

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Value of q • q is the square root of q 2 • q 2 = .0005

• Square root of .0005 = .022

• What is p?

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Value of p • p + q = 1 • Since q = .022

• Then p = .978 (1-.022) • What are the values for p 2 and 2pq?

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Values for p 2 and 2pq • P 2 = pxp =.978 x .978 = .956

• 2pq = 2 x .978 x . 22 = .043

• 4.3% of population are carriers for cystic fibrosis 23

Problem • Jack and Jill are expecting a baby. What is the chance the baby will have cystic fibrosis?

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Solution • The chance of Jack being a carrier is .043

• The chance of Jill being a carrier is .043

• The chance of two carriers producing a child with a recessive trait is .25

• .043 x .043 x .25 = .0046 @ 1/2000 25

Practical Application of Hardy Weinberg Equations • If you know the frequency of the recessive phenotype (aa) you can calculate the percent of the population that are carriers (Aa) and that are AA.

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Populations are rarely in Hardy Weinberg equilibrium • Most populations are evolving • Factors that cause allele frequencies to change – Nonrandom mating – Genetic drift – Gene flow – Mutation – Natural selection 27

Nonrandom Mating • Most people choose their mates based on – Physical appearance – Ethnic background – Intelligence – Shared interests • One-third of marriages are between people born less than 10 miles apart 28

Religious & Cultural Influences • Many people will only marry within their own religion or culture • Consanguineous marriages increase risk of birth defects by 2.5 times 29

Hopi Indians • Albinos stay in village with woman – Cannot tolerate the sun • Albinos have more opportunity to mate with females • 1/200 Hopi Indians are albino • 1/8 are carriers 30

Genetic Drift • Change in gene frequency when small a group of individuals leave or are separated from a larger population – Founder Effect – Bottleneck 31

Founder Effect Original Population 1% has allele A 10 Founders New Population 10% with A allele • 10 people leave to found a new population • 1 of the founders has allele A • 10% of new population will have allele A 32

Ellis-van Creveld Syndrome • Dwarfism • Extra fingers • Heart defects • High frequency in Amish population of Pennsylvania • A founder of the population had allele for the syndrome 33

Bottleneck • Population almost dies out • Survivors genes are at a higher frequency in the descendants than the original population 34

Cheetah Bottleneck • 2 major bottlenecks – 10,000 years ago – 1800’s • Present cheetah are more alike genetically than inbred lab mice 35

Gene Flow • When genes move from one population to another • Genes flow between the two populations below OKC Dallas 36

Gene Flow

• Can change the frequency of genes in a population • If gene flow stops for a long period of time the two populations may change enough from each other to become new species.

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No Gene Flow 38

Mutations • Introduces new alleles into a population • Most mutations are lethal – Mutation for no heart would be lethal • Some mutations are beneficial – Block infection of HIV 39

Beneficial Mutation • Mutation for albinism beneficial for bears who live on the ice and snow • Polar bears were once part of a population of brown & black bears • Now polar bears are a separate species 40

Natural Selection • Some individuals are more likely to survive and pass on their genes than others • Nature selects against gene for black fur in the arctic – Black fur does not enable bears in that environment to survive as well • Nature selects against gene for white fur in Oklahoma – White fur is not as advantageous in Oklahoma 41

Tuberculosis • Number 1 killer in 1900 • Antibiotics decreased cases dramatically • 1980 very few cases • Bacterium that causes TB is constantly mutating • Mutant strains resistant to antibiotics are naturally selected to survive 42

Evolution of Tuberculosis Cases of TB 1900 1980 2000 43

Sickle Cell Anemia Frequency • Sickle cell anemia is most common in parts of Africa with malaria • Carriers who live in an environment with malaria have an advantage – Immune to malaria 44

Why is the frequency of sickle cell anemia lower in the USA population of Blacks than African populations from which they originated?

• There is no selective advantage for the s allele in an environment with no malaria • The frequency of the s allele in the USA Black population has dropped significantly in the last 300 years.

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Stabilizing Selection

• Average value selected for • Extreme values selected against 46

Directional Selection

• Favors values above or below average • Population will shift to the favored value 47

Disruptive Selection

• Extreme traits are both favored • Birds with small bills and large bills are better feeders – In a specific enrironment 48

Macroevolution

• Evolution that results in new species 49

Allopatric Speciation

• A barrier separates a population into two subpopulations • There is no gene flow between the two populations • Each population changes with time • Changes result in new species.

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Sympatric Speciation

• Different individuals occupy different parts of the environment • They breed in the areas they occupy 51

Convergent Evolution

• Whales are mammals • Evolved a fish like body 52

Reptile

Divergent Evolution

Mammal Bird

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Coevolution

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Parallel Evolution

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Gradualism or Punctuated Equilibrium 56