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…

We describe the population in terms of distributions

…continuous variation

height

Figure 7.1

Fig 7.1

Average

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….

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.

fig 7-2

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%

Race

What does it mean?

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.,

Linnaeus: four “races”

White Europeans

Yellow Asians

Black Africans

Red Native Americans

Figure 7.3cRace

Based on culture:

Based on morphology (appearance):

Based on genetics:

Intelligence

Is there a genetic basis for “race”?

What is it?

How do you measure it?

(see page 212)

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

Figure 7.3a

fig 7-3

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

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?

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

Fig 7-6

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%)

fig 7-6

Sequence and compare mitochondrial DNA

Construct a tree to show relationships

Look for similarities and differences

fig 7-7

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.

What natural events help “select” humans?

Remember sickle cell anemia?

One of them is disease.

fig 7-10

fig 7-9

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.

Another disease:

Malaria

Figure 7.8

fig 7-8

fig 7-11

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)

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:

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

Figure 7.12

fig 7-12

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

Figure 7.13

fig 7-13