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0. Chapter 7. Human variation (and population genetics). 0. 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. 0.

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Chapter 7

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Chapter 7

Human variation

(and population genetics)


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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.


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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
Figure 7.1

Fig 7.1

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Average

continuous variation


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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


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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 allelefrequencies.

…….e.g., 41% of the population has type A blood


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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).


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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)



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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%


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Race

What does it mean?


Figure 7 3c
Figure 7.3c

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  • Race

    • Based on culture:

      • conquerer’s (us) vs. conquered (them)

      • dominate oppressed

  • World prior to ocean travel…

    • …very little mixing of cultures


Figure 7 3c1
Figure 7.3c

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  • Race

    • Based on culture:

  • Based on morphology (appearance):

  • subspecies (races)

  • skin color, hair texture, etc.,


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  • Linnaeus: four “races”

    • White Europeans

    • Yellow Asians

    • Black Africans

    • Red Native Americans


Figure 7 3c2
Figure 7.3c

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  • Race

    • Based on culture:

    • Based on morphology (appearance):

    • Based on genetics:


Intelligence
Intelligence

Is there a genetic basis for “race”?

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What is it?

How do you measure it?

(see page 212)


Figure 7 3c3
Figure 7.3c

Is there a genetic basis for “race”?

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Look at population genetics

  • Look at a single trait in different populations

  • What percentage of people havethe trait?


Figure 7 3c4
Figure 7.3c

Is there a genetic basis for “race”?

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Blood typing maps (pg. 214) (clines)

  • shows only indigenous people

    • (original inhabitants)

geographic variation


Figure 7 3a
Figure 7.3a

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fig 7-3


Is there a genetic basis for “race”?

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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:

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  • Blood typing

  • Injured soldiers on the battle field

  • (mid 1800’s)

A

B

O

not compatible with each other


Population genetics:

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Blood typing

Landsteiner (early 1900’s)

“A” carbohydrate on red blood cells A

“B” carbohydrate on red blood cells B

Neither O

Both (codominant) AB

  • A and B are antigens

    • (cause the immune system to attack)



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  • Rh system

  • C, D, E: close on same chromosome

  • Dominant/recessive

  • C, D, or E Rh positive

  • ccddee Rh negative



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Back to population genetics:

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  • 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


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  • Box 7.2 pp 222, 223

    • AA Aa aa

    • p2 + 2pq + q2 = 1



German Baptist Brethren (Dunkers)

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Fled Germany in 1719

Started colony in Pennsylvania

Strict rules (no marriage outside group)

  • If they were genetically typical 18th century Germans . . .


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  • 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.


  • (and if natural selection was working in Pennsylvania)

  • then they should have similar genetic make-up to their neighbors in PA.


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  • no type B blood (like Native Americans)

    • (Germans and Pennsylvanians have 6-8%)

  • No Fya blood type (like Africans)

    • (Europeans are mostly Fya )

Other traits: more German “looking” than Native American or African



Sequence and compare mitochondrial DNA

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Look for similarities and differences

Construct a tree to show relationships



What is the origin of differences in these different people groups?

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They have lived in different places (environments) and have been subjected to different selective pressures.

Remember the dark / light moths?


0 groups?

What natural events help “select” humans?

One of them is disease.

Remember sickle cell anemia?


0 groups?

fig 7-10


0 groups?

fig 7-9


Genetics of sickle-cell anemia groups?

HbA and HbS

normal diseased

HbA HbA normal

HbA HbS sickle-cell trait (some symptoms)

HbS HbS sickle-cell disease (often die young)


Genetics of sickle-cell anemia groups?

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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: groups?

Malaria

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Figure 7 8
Figure 7.8 groups?

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fig 7-8


fig 7-11 groups?


Is there a connection? groups?

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HbA HbA individuals infected with Plasmodium

(normal)

-severe symptoms

HbA HbS individuals infected with Plasmodium

(carrier)

-less severe symptoms (and fewer bites)


0


0


More Human differences: groups?

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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 groups?(geographic variation):

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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 groups?

Protruding parts (arms, legs) are shorter and thicker in cold areas and longer and thinner in warm areas.

rabbits and ears


Figure 7 12
Figure 7.12 groups?

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fig 7-12


More differences groups?(geography and climate):

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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
Figure 7.13 groups?

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fig 7-13


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