chapter 7 human variation (and population genetics)
TRANSCRIPT
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…
We describe the population in terms of distributions
…continuous variation
height
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….
We have gotten away from a morphological definition of species (like Aristotle used).
Evolution cannot work unless there is variation within a population.
…..population genetics
The textbook has two asides here:
Traits with continuous variation often are controlled by multiple genes as well as the environment.
(the distribution may differ)
The average for one population may be different than the average of another population.
Traits with discontinuous variation may also vary from one population to another...
“race” % with 0 blood
e.g., U.S. Caucasian 47%
African-American 49%
U.S. Asian 40%
Figure 7.3cRace
Based on culture:
conquerer’s (us) vs. conquered (them)
dominateoppressed
World prior to ocean travel…
…very little mixing of cultures
Figure 7.3cRace
Based on culture:
Based on morphology (appearance):
subspecies (races)
skin color, hair texture, etc.,
Figure 7.3c
Is there a genetic basis for “race”?
Look at a single trait in different populations
What percentage of people have the trait?
Look at population genetics
Figure 7.3c
Is there a genetic basis for “race”?
shows only indigenous people
(original inhabitants)
Blood typing maps (pg. 214) (clines)
geographic variation
Is there a genetic basis for “race”?
There are no unique genetic markers for “race”
Changes are gradual
Doesn’t correlate with “morphological races”
Great variability between A, B, o
“no 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)
ABO
not compatible with each other
Population genetics:
Blood typing
A and B are antigens (cause the immune system to attack)
“A” carbohydrate on red blood cellsA
Landsteiner (early 1900’s)
“B” carbohydrate on red blood cellsB
Neither OBoth (codominant) AB
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
Back to population genetics:
How do we keep track of the genetic make-up of a population?
IF:
Hardy-Weinberg principle
no migration
no selection
large population (with sexual reproduction)
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 Aa aa
p2 + 2pq + q2 = 1
German Baptist Brethren (Dunkers)
If they were genetically typical 18th century Germans . . .
Strict rules (no marriage outside group)
Started colony in Pennsylvania
Fled Germany in 1719
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 . . .
then they should have similar genetic make-up to their neighbors in PA.
(and if natural selection was working in Pennsylvania)
The Dunkers:
Other traits: more German “looking” than Native American or African
No Fya blood type (like Africans)
(Europeans are mostly Fya )
no type B blood (like Native Americans)
(Germans and Pennsylvanians have 6-8%)
Sequence and compare mitochondrial DNA
Construct a tree to show relationships
Look for similarities and differences
What is the origin of differences in these different people groups?
Remember the dark / light moths?
They have lived in different places (environments) and have been subjected to different selective pressures.
Genetics of sickle-cell anemia
HbS HbS sickle-cell disease (often die young)
HbA HbS sickle-cell trait (some symptoms)
HbA HbA normal
normal diseased
HbA and HbS
Genetics of sickle-cell anemia
WHY?
In some parts of Africa the frequency of the HBS allele is over 25%
So… check in Africa
In the US and Caribbean, most people with sickle-cell problems were of African descent.
Is there a connection?
HbA HbS individuals infected with Plasmodium
HbA HbA individuals infected with Plasmodium
-severe symptoms
-less severe symptoms (and fewer bites)
(normal)
(carrier)
More Human differences:
There were differences between “groups”
cold
hot and dry
heat and humid
Tolerance of different conditions:
pg. 236
african
european
native american
More Human differences (geographic variation):
Protruding parts (arms, legs) are shorter and thicker in cold areas and longer and thinner in warm areas.
body size is larger in cold areas and smaller in warm areas
Allen’s rule
Bergmann’s rule
Protruding parts (arms, legs) are shorter and thicker in cold areas and longer and thinner in warm areas.
Allen’s rule
rabbits and ears
More differences (geography and climate):
Sunlight (UV) is needed to make Vitamin D
Vitamin D is needed for normal growth
darker in warmer (sunnier) regions
Species are paler in colder regions
Gloger’s rule
Too much UV- cancer and folate deficiency