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Evolution, Part II

BIO 2215

Oklahoma City Community College

Dennis Anderson

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Major Elements Of Life

• Carbon• Hydrogen• Oxygen• Nitrogen

C

OH

N

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Chemical Evolution

• Carbohydrates• Fatty Acids• Amino Acids

Simple Molecules

OCO

H O H

HNH

H

HCH

H

H

More Complex Molecules

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

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Cyanobacteria

• Photosynthesis– Produce oxygen– Produce

carbohydrates

Carbon Dioxide + Water = Glucose + Oxygen

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Microevolution

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

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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

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Terms

• Codominance– Both alleles are dominant, AB blood type

• Gene Pool– All the alleles in a population

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Math Explains Allele Frequencies

• p + q = 1

• p = percent of dominant alleles in a population

• q = percent of recessive alleles in a population

• If 70% of alleles in a population are dominant then 30% must be recessive

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Genotype Frequencies

• Square the equation p + q = 1

• p2 + 2pq + q2 = 1

• Correlation between genotypes and variables in the equation are:

• p2 = AA

• 2pq = Aa

• q2 = aa

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Hardy-Weinberg Equations

• p + q = 1– Frequency of dominant alleles plus frequency

of recessive alleles is 100% ( or 1)

• p2 + 2pq + q2 = 1– AA plus 2Aa plus aa add up to 100% (or 1)

• Applies to populations that are not changing– They are in equilibrium

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Hardy-Weinberg Example

• Normal pigmentation (not albino) = A• Albinism recessive = a• AA = (p2) = normal• Aa = (2pq) = normal• aa = (q2) = 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

• p2 + 2pq + q2 = 1

• p2 = AA– .9929 x .9929 = .9858

• 2pq = Aa– 2 x .9929 x 0.00707 = .0140

• q2 = aa– .00005

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

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Cystic Fibrosis

• Cystic fibrosis affects 1 in 2000 white Americans

• Cystic fibrosis is recessive = cc

• 1 in 2000 = 1/2000 = .0005

• q2 = .0005

• What is q?

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Value of q

• q is the square root of q2

• q2 = .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 p2 and 2pq?

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Values for p2 and 2pq

• P2 = pxp =.978 x .978 = .956

• 2pq = 2 x .978 x . 22 = .043

• 4.3% of population are carriers for cystic fibrosis

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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

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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

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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

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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

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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

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Genetic Drift

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

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Founder Effect

• 10 people leave to found a new population• 1 of the founders has allele A• 10% of new population will have allele A

Original Population

1% has allele AFounders

New Population

10% with A allele

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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

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Bottleneck

• Population almost dies out

• Survivors genes are at a higher frequency in the descendants than the original population

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Cheetah Bottleneck

• 2 major bottlenecks– 10,000 years ago– 1800’s

• Present cheetah are more alike genetically than inbred lab mice

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Gene Flow

• When genes move from one population to another• Genes flow between the two populations below

OKC Dallas

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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

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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

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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

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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

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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

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Evolution of Tuberculosis

1900 20001980

Cases of TB

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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

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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

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Directional Selection

• Favors values above or below average

• Population will shift to the favored value

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Disruptive Selection

• Extreme traits are both favored

• Birds with small bills and large bills are better feeders– In a specific

enrironment

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Macroevolution

• Evolution that results in new species

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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

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Convergent Evolution

• Whales are mammals• Evolved a fish like body

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Divergent Evolution

Reptile

Mammal

Bird

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Coevolution

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Parallel Evolution

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Gradualism or Punctuated Equilibrium

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The End