Conserving Genetic Diversity. DNA arranged in discrete packages called Chromosomes. Units of Genetic Diversity . Individual portions of a chromosome that “code” for a specific character are known as Genes. Allele A1. Allele A2. Allele A3. Character E1. Character
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Conserving Genetic Diversity
DNA arranged in discrete packages called Chromosomes
Units of Genetic Diversity
Individual portions of a chromosome that “code” for a specific character are known as Genes
Alleles= alternate forms of a gene’s expression
Alleles on paired chromosomes
Gene Pool of a Population
Gene Pool = the complete genetic make up of a population
A5 alleles **
T3 alleles **
number of multiple allele genes divided by the total number of genes =
2/5 = 40%
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
Now let’s look at the genetic make-up of individual organisms
Remember- chromosomes are paired
5 Individual Organisms
2. T2/T3 **
3. T1/T3 **
4. T2/T1 **
the number of individuals who have different alleles in each pair of genes divided by the total number of individuals =
3/5 = 60%
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?
Given the following allele formulas, you provide the tail length of the individual
How can we get the following tail lengths?
T1/T1,T1/T2, T1/T3, T2/T1, T3/T1
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
Note: none of the elephant seals with alleles C, c, D, d, E, e, F, or f make it through the bottleneck
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
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!!
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
Causes of the Population Decline
Habitat Loss due to cutting of the forest by French Colonists
Egg predation by monkeys, rats and mongoose
“Varmint” shooting- alleged attacks on local chicken population
named “Mangeur des poules” by locals
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 can’t be helped
2. Those wounded slightly that don’t require help
3. Those whose wounds can be treated, resulting in survival
Specifically, mentions the Mauritius Kestrel as a Category 1 species
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
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
“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.
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.
% of total alleles in the popu-lation
Number of generations
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
Concept of Out-breeding Depression
“Hybrid” offspring of individuals from populations (geographic isolates) adapted to different environments
For example, individuals from an easternmigratory 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
Oryx distribu-tion in Africa consists of 9 non-overlapping populations comprising 4 species
Ibex - related to the Mountain Goat of North America
Occurs in many sub-populations, comprising at least 3 species throughout Europe and Asia
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