Genetic Diversity

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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.

What is biodiversity?

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.

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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.

Reducing Genetic Diversity

• Genetic bottlenecks• Founder effect• Artificial selection

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Genetic bottlenecks

Usually caused by a catastrophic, non-selective event (volcanic eruption/ice age etc.).

As a result, the number of different alleles is greatly reduced.

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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.

The elephant seal was hunted almost to extinction in the 1890s, reducing the gene pool.

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