Transcript Lab #8 Pop genetics

Population genetics is a field of
biology that studies the genetic
composition of biological
populations, and the changes
in genetic composition that
result from the operation of
various factors, including
natural selection.
AP Bio Lab #8
Population
Genetics
Part I PTC Paper
¯ PTC paper at front desk...
Tasters (p2 + 2pq)
Nontasters (q2)
Part I PTC Paper
*North American white population
0.45 0.55
*Japanese population 0.73 0.27
*Jewish population
0.47 0.53
*Hindu population
0.42
0.58
*Brazilian population 0.89 0.11
**Overall North American
0.55
0.45
Population genetics is a field of
biology that studies the genetic
composition of biological
populations, and the changes
in genetic composition that
result from the operation of
various factors, including
natural selection.
Ideal
Parameters
Everyone begins as a
heterozygote
Grab your gametes
children!!
Time to breed…
RANDOMLY!
Shuffle your gametes
children!!
Time to breed…
RANDOMLY!
Turn over the top
“gamete” on your pile
Lets just say…
Your gameteYour
partner’s
gamete
your F1
Time to breed…
RANDOMLY!
SHUFFLE AGAIN
Time to breed…
RANDOMLY!
Your gameteYour
partner’s
gamete
Your partner’s F1
Everyone takes the
genotype of their F1…
Grab your NEW 4
gametes!!
Time to mate…
RANDOMLY (go to
Shuffle your
someone
else)!new F1
gametes
Time to breed…
RANDOMLY!
Turn over the top
“gamete” on your pile
Time to breed…
RANDOMLY!
Your gameteYour
partner’s
gamete
your F2
And again… for the F3
generation
And again… for the F4
generation
And again… for the F5
generation
NO MATING OUT OF
TURN PLEASE!!!!
Selection
Selection
against
homo-recessive
Inflicted die before
reproductive age
If aa is drawn
your offspring will not
survive, draw again w/
same parents
Get gametes
for your F1
generation Aa
Inflicted die before
reproductive age
If aa, you die, shuffle
and draw again
heterozygote
advantage
heterozygote
advantage
Aa =
immune
Application of H-W principle
• Sickle cell anemia
– inherit a mutation in gene coding for
hemoglobin
• oxygen-carrying blood protein
• recessive allele = HsHs
–normal allele = Hb
– low oxygen levels causes
RBC to sickle
• breakdown of RBC
• clogging small blood vessels
• damage to organs
– often lethal
Sickle cell frequency
High frequency of heterozygotes
1 in 5 in Central Africans = HbHs
unusual for allele with severe
detrimental effects in homozygotes
1 in 100 = HsHs
usually die before reproductive age
Why is the Hs allele maintained at such high
levels in African populations?
Suggests some selective advantage of
being heterozygous…
Malaria
Single-celled eukaryote parasite
(Plasmodium) spends part of its
life cycle in red blood cells
Heterozygote Advantage
• In tropical Africa, where malaria is common:
– homozygous dominant (normal)
• die or reduced reproduction from malaria: HbHb
– homozygous recessive
• die or reduced reproduction from sickle cell anemia: HsHs
– heterozygote carriers are relatively free of both: HbHs
• survive & reproduce more, more common in population
Hypothesis:
In malaria-infected
cells, the O2 level is
lowered enough to
cause sickling which
kills the cell & destroys
the parasite.
Frequency of sickle cell allele
& distribution of malaria
If Aa is drawn
that is good…
If AA is drawn
This could be bad… flip a
coin to determine if it
survives
If AA is drawn
Heads = death
Tails = survive
Genetic Drift
Genetic Drift
Allele is lost… solely by
chance instead of via.
“selection”