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Transcript
When Hardy-Weinberg predictions
about future generations are…
When H-W equation does NOT accurately predict
gene frequencies for generation after generation,
it is safe to assume that the population is
evolving.
Populations may be evolving due to any or all of the
following 5 forces:
1. Mutations (flaws in replication leading to new genes)
http://perso.wanadoo.fr/corine.lundqvist/lundehund6toes.jpg
2. Migration (new individuals bringing new genes)
-animals can move to new areas, but so can pollen…
http://pollen.utulsa.edu/Image3.jpg
3. Genetic Drift
•changes in the gene pool of a small population
due to chance
•Leads to a loss of alleles and less variation
http://www.biol.andrews.edu/fb/spring/chap.23/2305.jpg
Ex: ”Bottleneck Effect”
Due to disasters like earthquakes,
floods, fires, over-hunting, or
diseases
http://www.si.edu/archives/thisday/
august/cheetah.jpg
-Cheetahs appear to
have gone through a
bottle-neck event
Genetic Drift (cont.)
Ex: Founder Effect: when few individuals start a new,
isolated population. Their alleles (good or bad)
become common.
Microcephaly in Old Order
Amish people of Lancaster
County, Pennsylvania
-61 babies in last 40 years
http://www.nlm.nih.gov/medlineplus/
ency/images/ency/fullsize/17256.jpg
Huntington’s Disease in Type O blood in South
Venezuela
and Central American
-most descended from
Indians
Maria Concepción Soto
http://anthro.palomar.edu/synthetic/synth_5.htm
4. Nonrandom Mating (certain genotypes mate
more often than expected if mating is random)
-mating with similar genotypes
-inbreeding
http://www.oceanwanderers.com/BlueGoose.6755.JPG
Snow geese come in two colors: blue and white. They
prefer to mate with birds of the same color. Leads to
inflated rates of homozygous genotypes.
5. Natural Selection (individuals of certain
genotypes leave behind more offspring than other
genotypes)
http://library.thinkquest.org/C003763/images/origin/finches.jpg
Darwin’s Finches (Galapagos Islands)
What advantage does it give a species to have
variation in genes? Why not just have the “best”
gene for all offspring?
It gives a species a way to change (adapt) if necessary.
“Evolutionary spurts occur when a population is stressed
by a change in the environment, migration to a new place,
or a drastic change in the genome. When challenged with
a new set of problems, a population either adjusts
through natural selection or it becomes extinct. The
fossil record indicates that extinction is the more
common outcome. Those populations that do survive
crises often change enough to become a new species…”
Biology, Campbell, p450