Transcript Genetic Variation within Populations

Genetic Variation within
Populations
11.1
• Gene Pool: the combined alleles of all of
the individuals in a population
• Allele frequency: How common a certain
allele is in a population
The Darwin awards: get these
people out of the gene pool!
In Modesto, California, Steven Richard
King was arrested for trying to hold up a
Bank of America branch without a
weapon. King used a thumb and a finger
to simulate a gun, but unfortunately, he
failed to keep his hand in his
pocket.(hellllllooooooo!)
The Darwin awards: get these
people out of the gene pool!
• WHAT WAS PLAN B???
An Illinois man, pretending to have a gun,
kidnapped a motorist and forced him to
drive to two different automated teller
machines, wherein the kidnapper
proceeded to withdraw money from own
his bank accounts.
The Darwin awards: get these
people out of the gene pool!
THE GETAWAY!
A man walked into a Topeka, Kansas
Kwik Stop, and asked for all the money in
the cash drawer. Apparently, the take was
too small, so he tied up the store clerk
and worked at the counter himself for
three hours until police showed up and
grabbed him.
The Darwin awards: get these
people out of the gene pool!
DID I SAY THAT???
Police in Los Angeles had good luck with a
robbery suspect who just couldn't control
himself during a line-up. When detectives
asked each man in the line-up to repeat
the words: "Give me all your money or I'll
shoot," the man shouted, "That's not what
I said!"
The Darwin awards: get these
people out of the gene pool!
• ARE WE COMMUNICATING??
A man spoke frantically into the phone,
"My wife is pregnant and her contractions
are only two minutes apart!" "Is this her
first child?" the doctor asked. "No!" the
man shouted, "This is her husband!"
Genetic variation comes from
several sources
• Mutation (random error in DNA)
• Recombination (crossing over in meiosis I)
Quick Quiz Review
• Why aren’t mutations in somatic cells sources of
genetic variation?
• Why does genetic variation increase the chance
that some individuals in a population will
survive?
• Describe two main sources of genetic variation.
• In what way is a gene pool representative of a
population?
• If a certain trait’s allele frequency is 100%,
describe the genetic variation for that trait in the
population.
11.2 Natural Selection in
Populations
• Natural selection acts on distributions of
traits
• Most traits have a normal distribution (bellshaped curve)
Natural Selection can change the
distribution of a trait in one of three
ways
• Directional selection
• Stabilizing selection
• Disruptive selection
Directional Selection
• This favors phenotypes at one extreme of
a trait’s range
• Ex: bacteria with a high resistance to
antibiotics are able to out-survive bacteria
with a low resistance to antibiotics. Soon
the average bacteria has a high resistance
to antibiotics.
Stabilizing Selection
• The intermediate phenotype is favored
(survives and reproduces more)
• Ex: the gall fly. If it makes a gall that is too
big, a woodpecker will eat it; if it makes a
gall that is too small,
a wasp will eat it.
• Goldilocks syndrome
Disruptive Selection
• When both extremes of phenotype are
favored.
• The opposite of stabilizing selection
• Ex: blue bunting birds get mates because females are attracted to
blue feathers. Brown bunting birds get mates because they are not
viewed as competition (so no dominant blue birds guard the females
against them.)
Quick Review
• In terms of phenotypes, describe what is meant
by the phrase “distribution of traits.”
• What are the three ways in which natural
selection can change a distribution of traits?
• How might the extinction of woodpeckers affect
the phenotypic distribution of gall flies?
• How might overfishing of large pink salmon
select for smaller body size in subsequent
generations?