10 27-11

Lab Intro: Genetic Drift

But first….

Evolution Review What is natural selection? How does natural selection relate to the struggle to

survive? – What are some environmental factors that create that struggle

Explain the concept of overproduction of offspring – How does that relate to the idea of population capacity?

What is inherited variation? • Why is it so very important?

• What are some dangers of loosing it? How does all of this relate to differential reproductive

success?

Biodiversity Review

What is biodiversity? Explain what “biodiversity = stable

ecosystem” really means?– What constitutes a stable ecosystem?

How is biodiversity decreased? How is biodiversity increased? What are some consequences of a loss

of biodiversity?

Genetic Variation

A loss of genetic variation = a loss of what?

Why is genetic uniformity so dangerous?

And now.. GENETIC DRIFT!

Genetic Drift is: FLASHCARD ALERT: GENETIC DRIFT: Random, non-adaptive

change in the gene frequencies (aka genetic variation) of a population – What do you think they mean by non-adaptive?

Usually reduces genetic variation– Which genes get eliminated happens by chance

Affects smaller populations much more than large populations.

Two types: Bottleneck Effect & Founders Effect

Example: Population of flowers: Red and White Through random chance the elimination of the white

flower occurs (I.e it gets trod on) This loss in genes to a small population means that

certain combinations cannot reproduce Over time the small population of flowers will be all

red.

Natural Selection vs. Genetic Drift

QuickTime™ and a decompressor

are needed to see this picture.

The Bottleneck Effect

FLASHCARD ALERT: BOTTLENECK EFFECT: – A situation where a large population is

drastically reduced in size • Could be a result of:

– natural disasters

– Invasive species

– Epidemic etc. etc.

Which does what to the genetic variation of the population?

Example: The California Sea Otter

Past 10 years: dying at an alarming rate– Infected with Toxoplasma

Gondii– Increased pollution– Loss of habitat

Almost Extinct – 1990: <100 otters– 1993: 2,200 otters

Now scientists are again having issues with successful population growth – Result of the bottleneck effect.

Founder Effect

FLASHCARD ALERT: – FOUNDER EFFECT: colonization of a new

habitat by only a few individuals

Again: reduce of genetic variation In the right circumstances it will lead to

speciation and eventually evolution of new species – New environment - new challenges - different

adaptations are beneficial - natural selection

Example: The Afrikaner population of Dutch Settlers in Africa Dutch immigrants in

1652 One man carried the

gene for Huntington’s disease – Dominant gene

Now there is an alarmingly high frequency of the disease in that region of Africa