Genetic Drift

What is it?

A sampling error problem

Imagine you are flipping a coin…

Genetic drift is important only when populations are SMALL

ways for a population to end up small…?

BottlenecksFounder events

Imagine you have all the genes from a single locus of a single population in a bottle…

Is genetic drift an example of evolution?

Examples of bottlenecking/founder events……

Humans

•Pingelap Atoll 20,000 pop dropped to 20 in 1775-Typhoon

At least 1 of the 20 carried an allele that

when homozygous=loss of vision

Conservation examples…

Elephant seals

Northern’s reduced to 20(?) in the 1890s

Now about 30,000

24 loci

Southern pop has abundant variation

Cheetahs

52 loci and found no diversity

skin transplants not rejected (MHC)

Low sperm counts

High infant mortality

Disease susceptibility

Florida Panther=Puma=Cougar=Mountain lion

Roelke et al. (1993).

Nearly as low as Cheetahs

With Fresh Blood, Inbred Florida Panthers ReboundBy Robert Roy BrittLiveScience Managing Editorposted: 18 August 200510:26 am ETA controversial breeding program has improved the genetic diversity of inbred Florida panthers and the endangered animals are on the rebound, scientists announced today.

As few as 30 wild panthers roamed the Florida Everglades in the early 1990s. Abnormalities such as low sperm counts and heart defects were becoming common, studies found, and the kittens had low survival rates.

In 1995, researchers outfitted some female Texas panthers with radio collars and introduced them into four sections of the Florida Everglades. Some Florida panthers were also tagged.

Researchers monitored the cats and kittens and found that the hybrids had better survival rates, presumably because they were more genetically diverse. By 2003, three of the Texas panthers were still alive, and they were removed -- scientists figured enough fresh blood had been injected into the Florida population and they wanted to keep outside genetic exposure to a minimum.

Today, there are at least 87 wild panthers in Florida.

"More than three times as many hybrid kittens appear to reach adulthood as do purebred ones," Pimm and his colleagues write in a paper that will be published early next year in the British journal Animal Conservation.

And the hybrids are on the move. The purebred panthers rarely ventured beyond protected areas north of interstate 75 and west of State Highway 29. Hybrid offspring have moved south and east into new sections of the Everglades National Park and Big Cypress National Preserve. They're pushing into places that are less hospitable, but they're doing so with success, the scientists said.

The federal government has decided that the hybrids will be called Florida panthers for purposes of determining their endangered species status.

Mongolian Wild Horse/Przewalski’s Horse

Foals captured in Mongolia in 1800s and shipped to Europe

(After 1945 only two captive populations in zoos remained, in Munich and Prague. The most valuable group, in the Ukraine, was shot by German soldiers during WWII. ….By the end of the 1950s, only 12 individual Przewalski's horses were left in the world). Wikipedia…

Went extinct in wild in 1960s

9 used to start a breeding program

Reintroduced to Mongolia

Currently reproducing in wild!

Review

In very small populations (bottlenecks, founder events) variation is lost (alleles are lost)

AND

rare alleles can become common

common alleles might become less common

Due to random changes in gene frequency

not a result of selection, mutation or immigration.

Gene flow

movement of …..individuals or gametes…. between populations

tends to reduce differences between populations that have accumulated because of natural selection or genetic drift…..

Gene flow is a big issue in the 21st century!

How are we genetically modifying crops?•Herbicide tolerance-roundup ready corn•Insect resistance…

HT=herbicide tolerance

Bt =insect resistance

http://blogs.ei.columbia.edu/2011/06/23/climate-ready-crops-the-pros-and-cons/

Most of the world‘s major crops naturally hybridize with wild relatives somewhere in the world……

(corn, mustards, sunflowers, squash, carrots and strawberries)

Why is this a problem?

Mexico to start experimental planting of GMO cornhttp://www.reuters.com/article/idUSN0424072320090604Thu Jun 4, 2009 6:24pm EDT

MEXICO CITY, June 4 (Reuters) - Mexico, considered the birthplace of corn, is reviewing more than two dozen requests to begin experimental planting of genetically modified crops, the agriculture ministry said on Thursday.

He said U.S. biotech food producer Monsanto Co (MON.N) is one of the companies who have applied for a permit to begin planting.

Supporters of GMO food, whose DNA is altered to be resistant to pests, say they boost yields. More than 70 percent of U.S. corn is genetically modified.

But farmers in Mexico's rural south, where corn has been grown for thousands of years, worry GMO corn will cross-pollinate with native species and alter their genetic content.

Corn was first planted in Mexico some 9,000 years ago and the country is now home to more than 10,000 varieties. The grain was adopted by Spanish conquistadors in the early 1500s and eventually spread to the rest of the world.

Under the current rules, GMO corn seeds are not allowed into certain parts of the country that are determined to be "centers of origin" for genetically unique corn strains found only

in Mexico.

Genetic Variation

What is it?

Why is variation important?

Where does new variation come from?

Mutation

Sexual reproduction-Recombination-Shuffling of alleles.

What was the Red Queen Hypothesis for the evolution of sex?

How is variation preserved? (back of Chapter)

Diploidy…why does this preserve variation?

Selection itself may preserve variation-how?

Niels Dingemanse University of Groningen, Netherlands

Genetic variation underlying exploration behavior in small birds!

Some highly exploratory others more cautious

When food scarce-who does well?

When food common –who does well?

Gene flow study with this

Species…(Gene Flow p410)

Evolutionary Psychology…

“Why do we all have different personalities?

Why hasn't natural selection homed in on optimum character traits instead of allowing so much variability?

As the study of personality moves to a more scientific footing, we are starting to understand the underlying neurobiology, and to see that each personality trait is beneficial in certain circumstances and costly in others.

We may tend to think that some personality types are more desirable than others, but these new insights make it clear that there is no "best" personality. It really does take all sorts to make a world.”Nettle, New Scientist Feb 2008

Another way selection preserves variation

Aa “do best” or have highest fitness

(AA get Malaria, aa get sickle cell disease)

What is this called?

Frequency dependent selection

Rare individuals have higher fitness..

“it is good to be unusual”

EX. Scale eating fish in text p415