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Human Variation

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Title: Human Variation


1
Human Variation
  • (Chapter 7)

2
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.

3
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.

4
Human Variation
  • Phenotype
  • An organisms physical traits
  • Genotype
  • An organisms genetic makeup

5
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

6
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

7
Human Variation
  • With origins in Africa, modern man has spread
    around the globe. In doing so, modern man
    adapted to the surroundings.

8
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.

9
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
10
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
11
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
12
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.

13
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.

14
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

15
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

16
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

17
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.

18
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
19
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.
20
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
21
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.
22
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
23
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.
24
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.

25
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.

26
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

27
Figure 7.5 (1)
Hemolytic disease
28
Figure 7.5 (2)
Hemolytic disease
29
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.

30
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.

31
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

32
Figure 7.8 (1)
Malaria an agent of natural Selection
33
Figure 7.8 (2)
Malaria an agent of natural Selection
34
Figure 7.8 (3)
Malaria an agent of natural Selection
35
Figure 7.8 (4)
Malaria an agent of natural Selection
36
Figure 7.8 (5)
Malaria an agent of natural Selection
37
Figure 7.8 (6)
Malaria an agent of natural Selection
38
Figure 7.9
Malaria an agent of natural Selection
39
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.

40
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
41
Figure 7.10
A small change in a gene can have many
phenotypic consequences.
42
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.

43
Malaria an agent of natural Selection
44
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.

45
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46
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.

47
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

48
The end!
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