Human Variation

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Human Variation

• (Chapter 7)

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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.

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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.

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Human Variation

• Phenotype

• An organisms physical traits
• Genotype
• An organisms genetic makeup

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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

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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 (non-random)
• Therefore, these genetic traits become dominant
  in a given population.
• Due to environmental pressure and natural
  selection

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Human Variation

• With origins in Africa, modern man has spread
  around the globe. In doing so, modern man
  adapted to the surroundings.

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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.

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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
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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).
• An AABBCC person would have very dark skin
• An aabbcc person would have very light skin

AABBCC (very dark)
aabbcc (very light)
AaBbCc
AaBbCc
Eggs
Sperm
Figure 9.22
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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 dark)
aabbcc (very light)
AaBbCc
AaBbCc
Eggs
Sperm
Figure 9.22
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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.

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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.

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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

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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

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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

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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.

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Figure 7.4
Why does this happen?
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-Acetylglucosam
ine, galactose and fucose Also known as antigens
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Figure 7.4
Why does this happen?
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.
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Figure 7.4
Why does this happen?
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
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Figure 7.3a
Human Blood Groups
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.
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Figure 7.3b
Human Blood Groups
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
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Figure 7.3c
Human Blood Groups
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.
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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.

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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 co-dominance,
  c, d, and e are recessive to C, D, and E.
• ccddee is known as Rh-negative. All others
  Rh-positive.

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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

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Figure 7.5 (1)
Hemolytic disease
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Figure 7.5 (2)
Hemolytic disease
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Figure 7.5 (3)
Hemolytic disease

• 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.

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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.

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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

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Figure 7.8 (1)
Malaria an agent of natural Selection
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Figure 7.8 (2)
Malaria an agent of natural Selection
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Figure 7.8 (3)
Malaria an agent of natural Selection
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Figure 7.8 (4)
Malaria an agent of natural Selection
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Figure 7.8 (5)
Malaria an agent of natural Selection
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Figure 7.8 (6)
Malaria an agent of natural Selection
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Figure 7.9
Malaria an agent of natural Selection
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Malaria an agent of natural Selection

• Sickle Cell Anemia
• Controlled by intermediate phenotypes at a ratio
  of 121
• 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.

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Malaria an agent of natural Selection
- Remember mutations? Any change in the
nucleotide sequence of DNA
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Sickle-cell hemoglobin
Normal hemoglobin
Glu
Val
Figure 10.21
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Figure 7.10
A small change in a gene can have many
phenotypic consequences.
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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.

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Malaria an agent of natural Selection
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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.

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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 1940s 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.

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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

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The end!

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