geneticdiversity kuliah s1
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Genetic DiversityBiology/Env S 204
Spring 2009
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Genetic diversity
Heritable variation within and betweenpopulations of organisms
Encoded in the sequence of 4 base-pairs that make up DNA
Arises by mutations in genes
and chromosomes
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Genetic Diversity
Very small fraction of genetic
diversity is outwardly expressed Estimated 109different genes across
the Earths biota
Represents a largely untapped genetic
library
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Genetic Diversity
Genetic diversity is the foundation forall higher levels of biodiversity
Genetic diversity provides the recipefor populations and species, which inturn form communities and ecosystems
Genetic variation enables evolutionary
change and artificial selection
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Genetic Diversity
Genetic diversity may have direct economicvalue (genes for disease resistance,
biologically active compounds) But effective conservation for whatever
purpose depends upon accurate, thoughtfulassessment of genetic diversity
Preservation of genetic diversity is usuallya high priority in conservation programs
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Nature of Genetic Diversity
Information for all of life
stored in the structure
of DNA Genetic code or the units
(bases, nucleotides) that
make up DNA areessentially universal
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Nature of Genetic Diversity
A length of DNA (often with extraproteins) is a chromosome
A section of DNA along thechromosome that contains theinformation to make a protein (orRNA) is a gene
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chromosome
gene gene
gene gene
Chromosome structure
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DNA Structure
A
T
T
GC
T
G
G
A
CA
T
T
A
A
CG
A
C
C
T
GT
A
A = adenineT = thymine
C = cytosine
G = guanine
Bases:
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Nature of Genetic Diversity
A gene may be several hundred to upto about two thousand units (bases)long
A gene contains the information tomake a protein or RNA
A gene is a discrete unit ofhereditary information
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Nature of Genetic Diversity
gene protein (enzymes, membranes, etc.)
RNA (essential for productionof proteins)
gene
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Nature of Genetic Diversity
A given gene may have more than one form;the different forms of a single gene arecalled alleles.
flower colorgene withtwo alleles
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Nature of Genetic Diversity
flower color
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Nature of Genetic Diversity
Homozygous(both alleles in anindividual are the same)
Heterozygous(two different allelespresent in an individualfor one gene)
or flower colorgene
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Nature of Genetic Diversity
Prokaryotes vs. Eukaryotes
bacteria,archaebacteria
protists, fungi,plants, animals
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Prokaryotes
One-celled, no compartments (nonucleus)
Genetic material in a single, circularchromosome
Therefore only 1 copy of each geneper bacterium
A typical bacterium has 1,000-2,000genes
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Eukaryotes
One-celled or many-celled, withcompartments (e.g., a nucleus is present)
Genetic material in two to many linear,separate chromosomes in the nucleus
Normally two copies of each gene presentin an individual in part of the life cycle
A eukaryote has about 50,000 genes onaverage
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Origin of Genetic Diversity
Mutation = change in the sequence ofbases of DNA along a chromosome
Change in a base or chunks of DNAcan be rearranged
Mutations can occur anywhere along achromosome
This is the ultimate source of allgenetic variation
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Measuring Genetic Diversity
Chromosome = a collection of genesplus extra DNA in between thatdoesnt code for anything
Genes are used in measuring geneticdiversity but
The extra DNA is free to changeand is also useful in assessing geneticdiversity
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Measuring Genetic Diversity
Different parts of the DNA evolve atdifferent ratesextra DNA changesfaster than DNA in the genes
Some genes evolve slowly and help inthe study of deep branches of life(ancient lineages)
Extra DNA can change so rapidlythat every individual is distinct(except for clones)
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Measuring Genetic Diversity
Within an individual: %heterozygosity (alleles same ordifferent in a given set of genes)
Among individuals in a population:allele frequencies for given genes
Between populations: %heterozygosity, allele frequencies,unique molecular markers
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Measuring Genetic Diversity
Measuring diversity betweenevolutionary lineages usuallyinvolves comparing sequences ofDNA and looking for changes in
bases or major rearrangments.
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Measuring Genetic Diversity
Loss of genetic diversity = loss ofuseful genetic diversity in theshort term and reduction ofevolutionary options in the long
term.
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Evolutionary Processes
1) Natural Selection
2) Gene Flow
3) Genetic Drift
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Evolutionary Processes1) Natural Selection
A major mechanism of evolution as proposedby Darwin
A filter for genetic variation: the best
adapted individuals survive and reproduce ingreater numbers over time
Not a directed process!
Changes in direction and intensity dependon conditions and time span and availablegenetic diversity
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Evolutionary Processes1) Natural Selection
SURVIVORhttp://science.discovery.com/interactives/literacy/darwin/darwin.html
http://science.discovery.com/interactives/literacy/darwin/darwin.htmlhttp://science.discovery.com/interactives/literacy/darwin/darwin.html -
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Evolutionary Processes2) Gene Flow
The exchange of genetic materialwithin a population, betweenpopulations of a species, and even
between species Gene flow among populations of aspecies maintains the integrity of thespecies
Lack of gene flow can lead tospeciation
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Evolutionary Processes2) Gene Flow
Population A
Population B
geneflow
A
B
barrierarises
Species A
Species B
reproductiveisolation
time
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Evolutionary Processes2) Gene Flow
Species A
Species B
geneflow
allopatric speciation =
geographic isolation+
reproductive isolation
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Evolutionary processes2) Gene Flow
Species A
(AA)
X
Species B(BB)
Hybrid AB(infertile,cannot crosswith either
parent either)
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Evolutionary processes2) Gene Flow
Hybrid AB
Chromosomedoubling AABB (now sex
cells can beproduced!)
AA
X
AABB
AAB (infertile)
sex cell A
sexcellAB
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Evolutionary Processes2) Gene Flow
sympatric speciation =reproductive isolation of
parent species fromhybrid derivatives throughhybridization and
chromosome doublingwithout geographic isolation
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Evolutionary Processes3) Genetic Drift
Changes in the gene pool of a smallpopulation due to chance events
Founder effect = one or two
individuals disperse and start a newpopulation with limited geneticdiversity
Bottleneck = extreme reduction inpopulation size and therefore geneticdiversity
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Conservation Genetics
Involves the use of genetic dataand principles to guide
conservation activities
Genetics should be prominent in
the practice of conservation
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Conservation Genetics
1) Rate of evolutionary change in apopulation is proportional to theamount of genetic diversity available
2) Higher genetic diversity is usuallypositively related to fitness
3) Global pool of genetic diversity
represents all of the information forall biological processes (= geneticlibrary)
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Conservation Genetics
Small populations tend to lose
genetic diversity over time!!!
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Conservation Genetics
Habitat fragmentation and destructionnow produce and will continue toproduce small, isolated populations
Understanding the genetic status ofspecies and populations and theconsequences of small population sizes
is vital to conservation, management,and recovery efforts.
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Conservation Genetics
A major goal is to preservenatural patterns of genetic
diversity to the extent possibleto preserve options for futureevolutionary change.
greater prairie chicken example
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Conservation GeneticsExample: Prairie Chickens
35-year study of a remnant population ofprairie chickens in Illinois
In 1962, about 2,000 individuals present;in 1994, fewer than 50
Fertility and hatching rates declined
significantly, as did genetic diversity Translocation program established in 1992
to bring in birds from MN, KS and NE
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Conservation GeneticsExample: Prairie Chicken
By 1994, increased survival of youngprairie chickens was verified
By 1997, there were significant
increases in mean rates of fertilityand hatching
Once the main population in Illinois
became isolated, it began to loseviability and without intervention, itmost likely would have disappeared