Download 4 Genetic Diversity

Genetic Diversity
What is biodiversity?
Biodiversity is a measure of how varied an ecosystem is.
It can be measured in terms of genes, species or habitats.

Genetic diversity is a measure of how many variations
there are in the genetic code between individuals of a
particular species, or between different species.

Species diversity is a measure of how many
different species are present in an area, and how
many individuals of these species there are.

Habitat diversity is a measure of how many different
habitats are present in an area.
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How does genetic variation arise?
• Discuss the structure of DNA and the cell cycle
with your partner.
• Where could errors arise?
• What types of errors might occur?
• How does meiosis increase genetic variation?
What is an Allele?
What is
Meiosis?
• Two processes
contribute to
genetic
variation:
independent
segregation
and crossing
over.
The origin of genetic variation
Genetic variation is heritable. It is this variation that natural
selection acts upon. The causes of genetic variation are:
Mutation
Sexual recombination

deletion, addition or
substitution of a nucleotide

independent assortment of
chromosomes in meiosis

deletion or translocation
of part of a chromosome

crossing-over during meiosis

aneuploidy – loss or gain
of a single chromosome

random fertilization.

polyploidy – the addition
of whole chromosome sets.
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Reducing Genetic Diversity
• Genetic bottlenecks
• Founder effect
• Artificial selection
Genetic bottlenecks
Usually caused by a catastrophic, nonselective event (volcanic eruption/ice age
etc.).
As a result, the number of different alleles is
greatly reduced.
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The elephant seal was hunted
almost to extinction in the 1890s,
reducing the gene pool.
The cheetah population has an
exceptionally low genetic
diversity. This is thought to be
due to a very narrow bottleneck,
where only a single family group
survived the last ice age.
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Founder Effect: Polydactylism
Founder Effect: Polydactylism
• Polydactyly - extra fingers and/or toes - the
syndrome is commonly found among the Old
Order Amish of Pennsylvania.
• Genetically inherited diseases like polydactyly
are more concentrated among the Amish
because they marry within their own
community, which prevents new genetic
variation from entering the population.
Founder Effect: Polydactylism
• Traced back to one couple, Samuel King and
his wife, who came to the area in 1744.
• Now more common amongst the Amish than
the general US population.
Selective Breeding
(artificial selection)
Another way of reducing genetic
diversity
Muscle Cow
Selective Breeding
• Selection of individuals with the desired
characteristics (and therefore alleles) to
breed.
• It also involves stopping those without the
desired characteristics from breeding.
• Over many generations, the population will
only possess the desired characteristics, but
will have reduced genetic diversity.
Selective Breeding
Selective Breeding
Selective Breeding
Selective Breeding
Selective Breeding – Artificial
Insemination
• Collection of semen and introduction into the
reproductive tract by artificial means.
TASK
1. Complete the first line of the table with your
own ideas about how each factor decreases
genetic diversity.
2. Use a textbook to add further explanation
(2nd line).
3. Add some examples for each of the factors.
Further Research
Genetic Bottleneck
•
•
•
•
reduction in population size
alleles lost when large proportion of the population dies
less genetic variation in the survivors
when the population recovers, there is less variation in the alleles compared with
original population
The Founder Effect
•
•
•
•
a few individuals from a population colonise a new region
they have only a small fraction of the alleles of the original population
these alleles are not in the same proportion as the original population
the new population that results has less genetic diversity and different
proportions of alleles