Transcript Human Variation

Biology Today (BIOL 109)
Talk Six:
Human Variation
Chapters 18 & 19
Human Variation
• Genetics is the study of biological traits.
These traits are coded for in genes, which
are parts of chromosomes.
• An Allele is a variant of a gene. These can
be dominant or recessive, and these are the
basis of inherited traits, both structural and
behavioral.
• Chromosomes exist as homologous pairs.
Human Variation
• Somatic Cells - Non-sex Cells. Contain a
full compliment of chromosomes.
Characteristic to their species. Referred to
as the diploid number of chromosomes.
• Gametes - Sex Cells. Cell which carry
genetic information for sexual reproduction.
Contain one half the compliment of
chromosomes characteristic to their species.
Referred to as the haploid number of
chromosomes.
Human Variation
• Phenotype
– An organism’s physical traits
• Genotype
– An organism’s genetic makeup
Allele
• Allele: Alternate form of a gene at same position
on pair of chromosomes that affect the same trait.
• Dominant Allele: Capital Letter--O
• Recessive Allele: lowercase letter--o
• Homozygous Dominant--OO
• Homozygous Recessive--oo
• Heterozygous--Oo
a
P
P
Genotype:
PP
a
aa
B
b
Bb
•
•
•
•
•
•
Natural Selection
Variation in population
Variation inheritable
Some individuals survive and reproduce
better than others
Survival and reproduction are tied to
variation in traits among individuals (nonrandom)
Therefore, these genetic traits become
dominant in a given population.
Due to environmental pressure and
natural selection
Human Variation
• With origins in Africa, modern man has spread around the
globe. In doing so, modern man adapted to the
surroundings.
Human Variation
• Arms and legs are longer
and thinner in warm
areas of the planet –
shorter and thicker in
cold regions.
• Conserves heat in cold
regions by reducing
surface area
• Skin pigmentation is
darker the nearer the
equator to protect the
skin from UV.
Polygenic Inheritance
• The additive effects of two or more genes on a
single phenotype
Polygenic
inheritance
Single trait
(e.g., skin color)
Multiple genes
Visual Summary 9.5
Polygenic Inheritance
• Three genes inherited
separately
• The dark-skin allele for each
gene (A, B, and C) contributes
one “unit” of darkness to the
phenotype and is incompletely
dominant to the other alleles
(a, b, and c).
aabbcc
(very light)
AaBbCc
Eggs
AABBCC
(very dark)
AaBbCc
Sperm
• An AABBCC person would have
very dark skin
• An aabbcc person would have
very light skin
Figure 9.22
Polygenic Inheritance
• An AaBbCc person would have
skin of an intermediate shade
• As the alleles have an additive
effect, AaBbCc would produce
the same skin color as any
other genotype with just three
dark-skin alleles, such as
AABbcc.
• The inheritance of these
alleles leads to a wide range of
skin pigmentation in the human
population.
aabbcc
(very light)
AaBbCc
Eggs
AABBCC
(very dark)
AaBbCc
Sperm
Figure 9.22
Ice age Europe (18,000 years ago)
• Glacial ice 2km thick covers
much of Northern Europe
and the Alps.
• Sea levels are approx. 125m
lower than today and the
coastline differs slightly
from the present day.
• Human populations that
began their migration from
Africa 60,000 years earlier
were stopped by the ice.
Ice age Europe (18,000 years ago)
•
Due to the cold and the
need for food, the
populations of the day
waited the ice age out in
the three locations
shown on the map.
• These were the Iberian
Peninsula, the Balkans
and the Ukraine.
After the Ice age – 12,000 years
ago
• 12,000 years ago, the ice
retreated and the land has
become much more
supportive to life.
• The three groups of humans
had taken refuge for so long
their DNA had naturally
picked up mutations
• These three major population
groups account for approx
80% of Europe's present-day
population
Finally, from 8,000 years
ago
• Peoples from Africa that had
moved to the Middle East
developed the new technology
of agriculture and began
moving back into Europe.
• This was the last migration of
human population into Europe.
• Body shape and skin
pigmentation all changed due
to environmental pressure on
the genomes of these
separate populations
Different populations have
different blood groups
• Different populations of people have many
different genetic variations
• The easiest to study is blood type
• Like all other differences, it is all down to
the frequency an allele is passed on during
reproduction and environmental pressure
and natural selection
Human Blood Groups
• A, B, AB, and o
• First found during the Crimean war (1854 – 1856)
– British Army Surgeon kept records of successful blood
transfusions
• A to A and B to B worked
• A to B or B to A were always fatal
• Also found that o was the universal donor
– People with this type of blood can give it to anyone
• AB type people can receive blood from anyone
– Universal recipient.
Why does this happen?
Figure
7.4
Both type A and type B blood
have specific carbohydrates
which are on the surface of
the blood cells.
AB blood has both
carbohydrates
on the surface of the blood
cells
o blood has no carbohydrates
Carbohydrates are:
N-Acetylglucosamine,
galactose and fucose
Also known as antigens
Why does
this
happen?
Figure
7.4
Antigen: Molecule that
stimulates an immune
response, especially the
production of antibodies by
plasma B cells. Antigens are
usually proteins or
polysaccharides.
A person who receives
incorrectly matched blood will
make antibodies against the
blood group antigens.
Blood cells clump together in
blood vessels with fatal
results.
Why does
this
happen?
Figure
7.4
Controlled by three alleles
Allele A – dominant
has info for making antigen A
Allele B – dominant
has info for making antigen B
Allele o – recessive
produces neither antigen
AA & Ao gives rise to A type blood
BB & Bo give rises to B type blood
AB is co-dominant - AB type blood
oo is recessive – o type blood
Human
Blood
Groups
Figure
7.3a
At 10-35% frequency in most
populations of the world, the A
blood allele is most common.
The highest frequencies of A
are found in small, unrelated
populations, especially the
Blackfoot Indians of Montana
(30-35%), the Australian
Aborigines (40-53%), and the
Lapps, or Saami people, of
Northern Scandinavia (50-90%).
The A allele apparently was
absent among Central and South
American Indians.
Human
Blood
Groups
Figure
7.3b
The global frequency
patterns of the type B
blood allele.
Note that it is highest in
central Asia and lowest in
the Americas and
Australia.
However, there are
relatively high frequency
pockets in Africa as well.
Overall in the world, B is
the rarest ABo blood allele
Human
Blood
Groups
Figure
7.3c
The o blood type (usually resulting
from the absence of both A and B
alleles) is very common around the
world.
It is particularly high in frequency
among the indigenous populations of
Central and South America, where it
approaches 100%.
It also is relatively high among
Australian Aborigines and in
Western Europe (especially in
populations with Celtic ancestors).
The lowest frequency of o is found
in Eastern Europe and Central Asia,
where B is common.
Rh Factor
• There are four blood groups but eight blood
types.
• The Rh-factor!!
•
•
•
•
85% Positive (US population)
15% Negative
Genetic factor
Can cause Hemolytic Disease and death of
infants.
The genetics of the Rh factor
• Another blood grouping system independent
of ABo – the Rh-factor
– Again, three genes (alleles): located very close
together on the same chromosome.
• First C & c, second D & d, third E & e
• Unlike the ABo system there is no codominance, c, d, and e are recessive to C, D,
and E.
• ccddee is known as Rh-negative. All others
Rh-positive.
Hemolytic disease
• If a child is Rh+, a Rh- Mother can begin to produce
antibodies Rh+ red blood cells
– Rh factor crosses placenta and mother makes
antibodies
• In subsequent pregnancies these antibodies can
cross the placenta and cause hemolysis of a Rh+
Childs red blood cells.
– Can lead to mental retardation or death
• Prevented by giving Rh- women a Rh immunoglobulin
injection no later than 72 hours after birth.
Attacks any of the babies Abs in mother before
her own antibodies are produced
Hemolytic
disease
Figure 7.5
(1)
Hemolytic
disease
Figure 7.5
(2)
Hemolytic
disease
Figure 7.5
(3)
•Prevented by giving Rh- women
a Rh immunoglobulin injection no
later than 72 hours after birth.
•Attacks any of the babies Abs
in mother before her own
antibodies are produced.
Malaria – an agent of natural Selection
• As any species evolves, biological differences
among its population arise largely through natural
selection.
• Diseases are among the selective forces that can
result in genetic differences among populations.
• In disease-ridden areas of the world, natural
selection acts to increase the frequency of alleles
that confer partial resistance to a disease while
decreasing the frequency of alleles that leave
people susceptible to a disease.
Malaria – an agent of natural Selection
• New traits are produced by mutation and are then
subject to natural selection.
• The traits that survive are adaptations.
• Malaria causes 110 million cases of illness each year
– Close to 2 million deaths each year.
• Rare before the invention of agriculture
– Did much to change the selective pressure on human
populations
Malaria – an agent of natural Selection
Figure 7.8 (1)
Malaria – an agent of natural Selection
Figure 7.8 (2)
Malaria – an agent of natural Selection
Figure 7.8 (3)
Malaria – an agent of natural Selection
Figure 7.8 (4)
Malaria – an agent of natural Selection
Figure 7.8 (5)
Malaria – an agent of natural Selection
Figure 7.8 (6)
Malaria – an agent of natural Selection
Figure 7.9
Malaria – an agent of natural Selection
• Sickle Cell Anemia
• Controlled by intermediate phenotypes at a
ratio of 1:2:1
• Red blood cells are not concave
• Normal Hemoglobin (HbA). Sickle cell (Hbs)
• HbA-HbA-normal
Hbs-Hbs – sickle cell
• HbA-Hbs- have the trait
• Therefore, incomplete dominance.
Malaria – an agent of natural
Selection
- Remember mutations? Any change in the
nucleotide sequence of DNA
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Glu
Sickle-cell hemoglobin
Val
Figure 10.21
Figure 7.10
A small change in a gene
can have many phenotypic
consequences.
Malaria – an agent of natural Selection
• Most victims of malaria are young children
• Where malaria occurrence is high, so is the HBs
allele
– Odd, as Sickle Cell Anemia is nearly always fatal
before reproductive age
– HBs allele confers resistance to malaria
• So in areas of high occurrence to malaria, the HBs
allele may cause a genetic disorder, but increases
the overall fitness of a population where malaria
occurs.
Malaria – an agent of natural Selection
The concept of racism
• Racism has many meanings:
– All of them come down to the belief that some
group of people are better than others.
• In most cases, the motivation to conquer a
region comes first, the racist ideology comes
later
• Came about because people thought that a
different genetic trait was inferior to one(s)
they processed.
Polygenic Inheritance
• The additive effects of two or more genes on a
single phenotype
Polygenic
inheritance
Single trait
(e.g., skin color)
Multiple genes
Visual Summary 9.5
Polygenic Inheritance
• Three genes inherited
separately
• The dark-skin allele for each
gene (A, B, and C) contributes
one “unit” of darkness to the
phenotype and is incompletely
dominant to the other alleles
(a, b, and c).
aabbcc
(very light)
AaBbCc
Eggs
AABBCC
(very dark)
AaBbCc
Sperm
• An AABBCC person would have
very dark skin
• An aabbcc person would have
very light skin
Figure 9.22
The concept of racism
• They also believed that their “group
identity” was inherited and could not be
changed
– A view which has no basis in genetics
• In the 1940’s the Nazis exterminated 11
million Jews, gypsies and other groups
– But not before theses groups were declared
“inferior”.
• Most people now regard racism as unethical
– Denies basic human rights, results in crime
and human conflicts.
Central High School in Little
Rock, Ark. 1957.
Elizabeth Eckford : Used
with permission from the media file repository of USHistory.com
The nicknamed "Little Rock Nine"
consisted of:
•
Ernest Green (b. 1941)
• Elizabeth Eckford (b. 1941)
• Jefferson Thomas (1942–2010)
• Terrence Roberts (b. 1941)
• Carlotta Walls LaNier (b. 1942)
• Minnijean Brown (b. 1941)
• Gloria Ray Karlmark (b. 1942)
• Thelma Mothershed (b. 1940)
• Melba Pattillo Beals (b. 1941)
With Permission © 2010 Marquette University
Systemic Power and Race
• P3 = power X Power X Power
• Power1 = Power over people of color
• Power2 = Power which gives and preserves privilege
and advantages for white people
• Power3 = Power which socializes all of us into the
racial rules
• Racism’s ultimate power – to control and racialize all
of us
The concept of racism
• Human populations have always been
variable.
– adapt and change under selective pressure
• Skin pigmentation is determined by a
selective environmental pressure due to the
total amount of sunlight a population exists
with.
• Taught hatred for different populations of
people
The end!
Any Questions?