Download Chapter 7

Chapter 7
Human variation
(and population genetics)
Population:
Individuals within a species that can
mate with each other in nature.
Biological variation (like Darwin saw) exists:
within a population.
between different populations.
Some traits differ over a wide range with lots of variation
in between…
height
…continuous variation
We describe the population in terms of distributions
Figure 7.1
Average
Fig 7.1
continuous variation
Some traits differ over a wide range with lots of variation
in between…
height
…continuous variation
Other traits follow the dominant/recessive pattern we
discussed earlier (blood type, Tay Sachs disease, etc.)…
…discontinuous variation
Other traits follow the dominant/recessive pattern we
discussed earlier (blood type, Tay Sachs disease, etc.)…
…discontinuous variation
We describe a population in terms of allele frequencies.
…….e.g., 41% of the population has type A blood
The study of genetic variation of populations is called….
…..population genetics
The textbook has two asides here:
Evolution cannot work unless there is variation
within a population.
We have gotten away from a morphological
definition of species (like Aristotle used).
Traits with continuous variation often are
controlled by multiple genes as well as the
environment.
The average for one population may be different
than the average of another population.
(the distribution may differ)
fig 7-2
Traits with discontinuous variation may also vary
from one population to another...
“race”
e.g.,
% with 0 blood
U.S. Caucasian
47%
African-American
49%
U.S. Asian
40%
Race
What does it mean?
Race
Figure 7.3c
Based on culture:
conquerer’s (us) vs. conquered (them)
dominate
oppressed
World prior to ocean travel…
…very little mixing of cultures
Race
Figure 7.3c
Based on culture:
Based on morphology (appearance):
subspecies (races)
skin color, hair texture, etc.,
Linnaeus: four “races”
White
Europeans
Yellow
Asians
Black
Africans
Red
Native Americans
Race
Figure 7.3c
Based on culture:
Based on morphology (appearance):
Based on genetics:
Is there a genetic basis for “race”?
Intelligence
What is it?
How do you measure it?
(see page 212)
Is there a genetic basis for “race”?
Figure 7.3c
Look at population genetics
Look at a single trait in different populations
What percentage of people have the trait?
Is there a genetic basis for “race”?
Figure 7.3c
Blood typing maps (pg. 214) (clines)
shows only indigenous people
(original inhabitants)
geographic variation
Figure 7.3a
fig 7-3
Is there a genetic basis for “race”?
Changes are gradual
Great variability between A, B, o
Doesn’t correlate with “morphological races”
“no race”
There are no unique genetic markers for “race”
concept used to suppress others, e.g., “racism”
slavery, Hitler’s Germany, anti-immigration
Population genetics:
Blood typing
Injured soldiers on the battle field
(mid 1800’s)
A
B
O
not compatible with each other
Population genetics:
Blood typing
Landsteiner (early 1900’s)
“A” carbohydrate on red blood cells A
“B” carbohydrate on red blood cells B
Neither
Both (codominant)
O
AB
A and B are antigens
(cause the immune system to attack)
fig 7-4
Other blood groupings:
ABO system
Rh system
C, D, E:
close on same chromosome
Dominant/recessive
C, D, or E
Rh positive
ccddee
Rh negative
fig 7-5
Other blood groupings:
ABO system
Rh system
MN, Duffey, others, …
Back to population genetics:
How do we keep track of the genetic
make-up of a population?
Hardy-Weinberg principle
IF:
large population (with sexual reproduction)
no selection
no migration
Hardy-Weinberg principle (equation)
Allele frequencies will stay the same, if…
large population (with sexual reproduction)
no selection
no migration
Box 7.2 pp 222, 223
AA
p2
+
Aa
aa
2pq +
q2
=1
Fig 7-6
German Baptist Brethren (Dunkers)
Fled Germany in 1719
Started colony in Pennsylvania
Strict rules (no marriage outside group)
If they were genetically typical 18th
century Germans . . .
If they were genetically typical 18th century
Germans . . .
(and Hardy Weinberg applies)
. . . then they should have similar genetic
make-up to other populations descended from
18th century Germans.
If they were genetically typical 18th century
Germans . . .
(and if natural selection was
working in Pennsylvania)
then they should have similar genetic make-up
to their neighbors in PA.
The Dunkers:
no type B blood
(like Native Americans)
(Germans and Pennsylvanians have 6-8%)
No Fya blood type
(like Africans)
(Europeans are mostly Fya )
more German “looking” than
Native American or African
Other traits:
fig 7-6
Sequence and compare mitochondrial DNA
Look for similarities and differences
Construct a tree to show relationships
fig 7-7
What is the origin of differences in these different
people groups?
They have lived in different places (environments) and
have been subjected to different selective
pressures.
Remember the dark / light moths?
What natural events help “select” humans?
One of them is disease.
Remember sickle cell anemia?
fig 7-10
fig 7-9
Genetics of sickle-cell anemia
HbA
and
normal
HbS
diseased
HbA HbA
normal
HbA HbS
sickle-cell trait (some symptoms)
HbS HbS
sickle-cell disease (often die young)
Genetics of sickle-cell anemia
In the US and Caribbean, most people
with sickle-cell problems were of
African descent.
So… check in Africa
In some parts of Africa the frequency of the
HBS allele is over 25%
WHY?
Another disease:
Malaria
Figure 7.8
fig 7-8
fig 7-11
Is there a connection?
HbA HbA individuals infected with Plasmodium
(normal)
-severe symptoms
HbA HbS individuals infected with Plasmodium
(carrier)
-less severe symptoms (and fewer bites)
Is there a connection?
Having the sickle-cell gene protects against
Malaria
Other genetic diseases also protect against
Malaria:
Thalassemia
G6PD deficiency
More Human differences:
Tolerance of different conditions:
heat and humid
african
hot and dry
native american
cold
european
There were differences between “groups”
pg. 236
More Human differences (geographic variation):
Bergmann’s rule
body size is larger in cold areas and
smaller in warm areas
Allen’s rule
Protruding parts (arms, legs) are shorter
and thicker in cold areas and longer and
thinner in warm areas.
Allen’s rule
Protruding parts (arms, legs) are shorter
and thicker in cold areas and longer and
thinner in warm areas.
rabbits and ears
Figure 7.12
fig 7-12
More differences (geography and climate):
Gloger’s rule
Species are paler in colder regions
darker in warmer (sunnier) regions
Vitamin D is needed for normal growth
Sunlight (UV) is needed to make Vitamin D
Too much UV- cancer and folate deficiency
Figure 7.13
fig 7-13