Conserving Genetic Diversity

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Conserving Genetic Diversity
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Units of Genetic Diversity
Individual portions of a chromosome that code
for a specific character are known as Genes
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Alleles alternate forms of a genes expression
Gene A
Character E
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Alleles on paired chromosomes
Homozygous
Heterozygous
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Gene Pool of a Population
Gene Pool the complete genetic make up of a
population
Genes A 5 alleles T 3 alleles C 1
allele D 1 allele E 1 allele
Polymorphism number of multiple allele genes
divided by the total number of genes 2/5 40
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For Example suppose that the gene (T)
controlling tail length has 3 different alleles
T1 codes for a tail that is 50 cm in length
T2 codes for a tail that is 100 cm in length
T3 codes for a tail that is 150 cm in length
Now suppose that due to random chance all three
tail lengths are equally likely to occur.
Thus, out of a population of 102 individuals,
there will be roughly 34 individuals possessing
each of the 3 different tail lengths
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Now lets look at the genetic make-up of
individual organisms
Remember- chromosomes are paired
5 Individual Organisms 1. T1/T1 2. T2/T3 3.
T1/T3 4. T2/T1 5. T2/T2
Heterozygosity the number of individuals who
have different alleles in each pair of genes
divided by the total number of individuals 3/5
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Introducing the Concept of Dominant and Recessive
Alleles
Our tail length example is not quite so simple -
suppose that when T1 and T2 are paired (e.g. the
formula is T1/T2 or T2/T1) the tail length is
always 50 cm .
That means that T1 is dominant over T2
What if T1 is also dominant over T3?
What if T2 is also dominant over T3?
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Given the following allele formulas, you provide
the tail length of the individual
Formula
Tail Length
T1/T1
50 cm
T1/T3
50 cm
T1/T2
50 cm
T3/T3
150 cm
T2/T3
100 cm
50 cm
T2/T1
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How can we get the following tail lengths?
50 cm
T1/T1, T1/T2, T1/T3, T2/T1, T3/T1
100 cm
T2/T2, T2/T3, T3/T2
150 cm
T3/T3
Heterozygous
Homozygous
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Concept of a Genetic Bottleneck
Forelimb alleles A, a, C, c, E, e
Uppercase dominant, lower case recessive
Tail alleles B, b, D, d, F, f
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Genetic Bottleneck
Note none of the elephant seals with alleles C,
c, D, d, E, e, F, or f make it through the
bottleneck
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Concept of Founder Effect
Founders those individuals from a population
that either disperse to another location or
survive some type of disturbance to its current
location.
Due to chance alone, the founders are usually
less genetically diverse than the source
population as a whole
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Concept of Founder Effect
Okapi, the African Forest Antelope
Zoo populations consisted of 75 wild caught
individuals
Of those, only 30 have bred, producing 23 living
offspring
But the resulting genetic structure was
equivalent to only 12 wild individuals!!
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A 1973 survey by International Council for Bird
Preservation located 8 wild kestrels
By the 1974 breeding season there were two birds
in captivity and four others known in the wild
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Causes of the Population Decline
Habitat Loss due to cutting of the forest by
French Colonists
Pesticide poisoning
Egg predation by monkeys, rats and mongoose
Varmint shooting- alleged attacks on local
chicken population named Mangeur des poules by
locals
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In the book The Sinking Ark, Norman Myers
states that, we should take a Triage approach
to species preservation.
1. Those so badly wounded that they cant be
helped
2. Those wounded slightly that dont require help
3. Those whose wounds can be treated, resulting
in survival
Specifically, mentions the Mauritius Kestrel as a
Category 1 species
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Aspects of a captive breeding program for
Mauritius Kestrels
1. Supplemental feeding of wild birds with
uncontaminated meat. Result, the females
double-clutched
2. Pulling of eggs. Result, clutch size was
increased to eight
3. Hacking - the gradual weaning of captive
young from human helpers. Result, young raised
by humans able to successfully compete in the wild
4. Artificial insemination of captive females.
Result, increased female fertility rates
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Field Aspects of a Conservation Program
1. Natural reserves. Result, the setting aside
of a small amount of human free habitat leading
to increase survival of adults and young.
2. Predator control. Result, reduction in egg,
juvenile and adult mortality
3. Public education. Result, reduction in adult
mortality due to varmint hunting
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If you can save the Mauritius Kestrel, you can
save virtually anything.
By 1990, two hundred captive breed Kestrels had
been successfully re-introduced to the Mauritius
Islands.
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Concept of Genetic Drift
Random fluctuations in the frequency of an allele
due to accidents that affect the survival and
reproduction of individuals.
Directly related to the number of individuals in
the population possessing the allele
Has the greatest effect on uncommon alleles.
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50 40 30 20 10
of total alleles in the popu-lation
5 10 15 20
Number of generations
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Concept of Inbreeding Depression
Inbreeding mating of closely related
individuals
Cheetah the victim of two genetic bottlenecks
Inbreeding depression poor survival or
production in populations where closely related
individuals mate
Often, the result of inbreeding depression is an
increase of homozygous recessive traits that are
deleterious
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Concept of Out-breeding Depression
Hybrid offspring of individuals from
populations (geographic isolates) adapted to
different environments
Peregrine Falcon
For example, individuals from an eastern
migratory population, adapted to harsh winters,
breed and produce offspring with mates from a
coastal non-migratory western population, adapted
for mild winters and early springs
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Oryx distribu-tion in Africa consists of 9
non-overlapping populations comprising 4 species
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Ibex - related to the Mountain Goat of North
America
Occurs in many sub-populations, comprising at
least 3 species throughout Europe and Asia
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The resulting young were born in midwinter,
resulting in high mortality and eventual
extinction of the introduced population
Introduction of individuals from two foreign
subspecies into the Tatry Mountains of Slovakia
and Poland