Week 5 Founder Effects, Inbreeding, Hybrid Zones Flashcards
What is the founder effect?
The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population
What is a human example of the founder effect?
The Amish population
Over the generations the number of descendants of these few founders has grown and the population has therefore expanded (although more people leave the community than join)
Why are the Amish highly valuable for genetic studies?
• excellentrecords
• largefamilysize
• restricted population
The allele frequencies in the Amish population are ….. of the communities from which they are descended in Europe
Atypical
Why are the allele frequencies atypical in Amish populations?
Founder events: the first 400 founders will have, by chance, had an atypical collection of genes
Further drift: the small population size subsequent to foundation will have exaggerated further genetic drift
Six of the founders names are responsible for 3/4 of those seen today and a full 1/4 are called Stoltzfus, this change in the frequency of names is most easily explained as what?
random or stochastic change
(Be careful: they might be associated with genes that confer a selective advantage)
What would be other examples of similar random or stochastic changes?
The same change would be predicted for Y chromosomes which are also transmitted down the paternal line
and a similar change for mitochondrial DNA which is passed down the maternal line
Rh –ve is almost certainly selected for or agaisnt?
agaisnt
Why would we expect to see greater
genetic drift on the Y chromosome compared with other parts of the genome?
Smaller effective population size
How can Rh –ve have reached high frequency when it is selected against?
Drift acts on all loci, Even those subject to selection
Ellis-van Creveld syndrome (Six fingered dwarfism) a recessive trait, and is only expressed when an individual carries two copies of the allele. It is extremely rare, however 1/7 of Amish population carry the gene. Why?
The allele may have subsequently drifted to high frequency
The Amish are a good example of what?
genetic drift
What are examples of bottlenecks in nature?
• Last Ice Age ended in the Pleistocene
• Quaternary Mass Extinction Event
• Ice Age, Climate, Humans
• Loss of 40 large mammals and mass reduction in others
What aminal is very lacking in genetic diversity?
Cheetahs
So similar you can graft skin from one cheetah onto another unrelated cheetah without anti- rejection drug
What is an example of human induced bottle necks?
• 60% of fish are overfished
• These populations are thought to have reduced heterozygosity and loss of rare alleles
they are not genetically varied, one disease can wipe out all
