Evolution, Part II
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Evolution, Part II. BIO 2215 Oklahoma City Community College Dennis Anderson. Major Elements Of Life. Carbon Hydrogen Oxygen Nitrogen. C. H. O. N. O. C. O. H. O. H. H. H. H. N. H. H. H. H. C. H. H. Chemical Evolution. Simple Molecules. More Complex Molecules.

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Evolution, Part II

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Evolution, Part II

BIO 2215

Oklahoma City Community College

Dennis Anderson


Major Elements Of Life

  • Carbon

  • Hydrogen

  • Oxygen

  • Nitrogen

C

H

O

N


O

C

O

H

O

H

H

H

H

N

H

H

H

H

C

H

H

Chemical Evolution

Simple Molecules

More Complex Molecules

  • Carbohydrates

  • Fatty Acids

  • Amino Acids


Carbohydrates


Fatty Acids


Amino Acids


Figure 02.12


Proteinoid Microspheres

  • Similar to protocells

  • Protocells

    • Reproduce

    • Natural selection favored those with the most efficient replicating systems

      • RNA

      • DNA


Cyanobacteria

  • Photosynthesis

    • Produce oxygen

    • Produce carbohydrates

CarbonDioxide + Water = Glucose + Oxygen


Microevolution

  • Change in allele frequency of a population

    • Populations evolve, individuals do not


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


Terms

  • Codominance

    • Both alleles are dominant, AB blood type

  • Gene Pool

    • All the alleles in a population


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


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


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


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


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


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


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?


Value of q

  • q is the square root of q2

  • q2 = .0005

  • Square root of .0005 = .022

  • What is p?


Value of p

  • p + q = 1

  • Since q = .022

  • Then p = .978 (1-.022)

  • What are the values for p2 and 2pq?


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


Problem

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


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


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.


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


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


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


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


Genetic Drift

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

    • Founder Effect

    • Bottleneck


New Population

10% with A allele

Founder Effect

Original Population

1% has allele A

10

Founders

  • 10 people leave to found a new population

  • 1 of the founders has allele A

  • 10% of new population will have allele A


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


Bottleneck

  • Population almost dies out

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


Cheetah Bottleneck

  • 2 major bottlenecks

    • 10,000 years ago

    • 1800’s

  • Present cheetah are more alike genetically than inbred lab mice


Gene Flow

  • When genes move from one population to another

  • Genes flow between the two populations below

OKC

Dallas


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.


No Gene Flow


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


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


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


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 naturallyselected to survive


Evolution of Tuberculosis

Cases of TB

1900

1980

2000


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


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.


Stabilizing Selection

  • Average value selected for

  • Extreme values selected against


Directional Selection

  • Favors values above or below average

  • Population will shift to the favored value


Disruptive Selection

  • Extreme traits are both favored

  • Birds with small bills and large bills are better feeders

    • In a specific enrironment


Macroevolution

  • Evolution that results in new species


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.


Sympatric Speciation

  • Different individuals occupy different parts of the environment

  • They breed in the areas they occupy


Convergent Evolution

  • Whales are mammals

  • Evolved a fish like body


Divergent Evolution

Mammal

Reptile

Bird


Coevolution


Parallel Evolution


Gradualism or Punctuated Equilibrium


The End


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