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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. 2 of 39 © Boardworks Ltd 2008 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. 6 of 37 © Boardworks Ltd 2009 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. 9 of 37 © Boardworks Ltd 2009 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. 10 of 37 © Boardworks Ltd 2009 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