Anthropology 103 Chapters 2 and 3

1
Anthropology 103Chapters 2 and 3
Group Work You have each been given a poster
board. As well, I have some markers available.
I would like your group to choose one issue,
example or concept from either chapter 2 or 3 and
prepare a poster board of that example or
concept. Your goal is to explain the idea as if
to a layperson. Have fun with the poster board
but be sure to define a specific area of focus.
Note this PowerPoint is presented without the
graphics.
2
Chapter 2 Human Genetics
3
Introduction
Our chapter opens with a question to which we
will return numerous times. That is, is human
behavior the result of biology or culture? Most
anthropologists acknowledge that human behavior
is a complex mix of both biological factors and
cultural ones. To be honest, most
anthropologists would probably feel that human
behavior is more closely tied to either
biological or cultural factors, but all
acknowledge the importance of the biocultural
perspective in anthropology. As well, we know
that as individuals we have our own belief
systems that might include our own preferences
for either the biological or the cultural.
4
Significant Reflection 1
Human Behavior and the Biocultural Perspective
Human Behavior Biological or Cultural? Humans
interaction of biological and cultural forces
The biocultural perspective in anthropology
5
From Physical to Biological
The very name of our subfield, Physical/Biological
Anthropology, offers an interesting
understanding of the changing perspectives on
humans as biocultural beings. Prior to the major
genetic discoveries, humans were understood
largely as physical beings. Scientists,
anthropologists and everyday citizens focused on
the perceived physical differences between
humans. Here is one such example of this earlier
conceptualization
6
From Physical to Biological
7
From Physical to Biological
This particular illustration comes from the work
of the preeminent physical anthropologist Hooten.
He, along with criminologists around the world,
believed that the physical characteristics of
humans allowed for meaningful determinations
about behavior. In this case, Hooten determined
that certain physical characteristics increased
ones likelihood of criminality,
8
From Physical to Biological
Much of this work on physicality and human
behavior is derived from nineteenth century
racialism--a doctrine that assumed that physical
race was in all ways meaningful. This assumption
produced academic and everyday reflections on
physicality.
9
From Physical to Biological
The example of the work of cultural evolutionists
illustrates the academic side of racialism.
10
From Physical to Biological
In the realm of popular culture, such as in the
1893 Columbian Exposition pictured here,
assumptions about race followed a similar theme,
11
From Physical to Biological
12
From Physical to Biological
Unfortunately, the midway of the 1893 exposition
served to perpetuate not only the racialism of
the evolutionists, but also the virulent racism
which would continue through WWII.
13
From Physical to Biological
Fortunately, pioneers like Franz Boas, the Father
of American Anthropology, fought both racialism
and racism in and outside of the academy.
14
From Physical to Biological
Boas combated the evolutionists by focusing on
their poor science. He was politically creative,
particularly as he rallied anthropologists
against racialism. He personally faced
anti-Semitism in the United States. Boas went on
to found the famous department of anthropology at
Columbia University.
15
From Physical to Biological
Boas work and that of many others in profiled in
George Stockings historical look at physical
anthropology in the United States.
16
From Physical to Biological
Even beyond the evolutionists, assumptions about
physicality and behavior continued. An example
is the emphasis on the physicality of the cranium
and the clues it offers to human psychology.
Phrenology is this example.
17
From Physical to Biological
Phrenology, like criminal anthropology, was based
on poor science and inaccurate assumptions about
physicality and human behavior. As the twentieth
century developed, unfortunate social events,
like the rise of fascism in Europe, led to
eugenics and genocide. The example of Nazism
confirms the danger of assumptions about race,
physicality and human behavior.
18
From Physical to Biological
Even today, people perceive meaning in physical
differences that, in reality, do not exist.
Evolutionary biologist Joseph Graves offers a
contribution to the layperson. His text
demonstrates the fallacies of racialism, even as
it continues today.
19
From Physical to Biological
Later in the quarter, we will more fully explore
the biological issues of race. This extended
reflection does allow us major insight into the
emergence of biological anthropology out of
physical anthropology. Simply put, contemporary
anthropologists understand that physicality is
not a determining factor in human behavior as it
was once understood. We owe this to
anthropologists like Boas and contemporary
genetic science.
20
Significant Reflection 2
Physicality, Race and Human Behavior
Physicality is not a significant factor in
understanding the behavioral conditions of
humans. Race is a social construct, NOT a
meaningful biological fact of humans.
Unfortunately, racialism continues to plague our
planet in the form of bigotry and genocide.
21
When Say Genetics We Mean.
In anthropology, when we say genetics we simply
mean inheritance. Were not talking about the
kind of inheritance that we might get from a
relative who passes away, but the idea is
similar. What were really trying to understand
in anthropological genetics is the process by
which different traits are inherited from parents
to their offspring. To what extent are humans a
reflection of their parents? This is an
important question asked by anthropological
genetics. So our simple definition of genetics
isinheritance.
22
When Say Genetics We Mean.
In anthropology, when we say genetics we often
mean inheritance. Were not talking about the
kind of inheritance that we might get from a
relative who passes away, but the idea is
similar. What were often trying to understand
in anthropological genetics is the process by
which different traits are inherited from parents
to their offspring. To what extent are humans a
reflection of their parents? This is an
important question asked by anthropological
genetics.
23
When Say Genetics We Mean.
In addition to understanding inheritance and
heredity, we can say that anthropological
genetics also means biological variation.
Physical anthropologists are interested in
describing the patterns of genetic variation
within and among different populations. We can
study both short-term evolutionary changes in
populations (microevolution) and long-term
evolutionary change (macroevolution). Based on
both of our understanding
24
When Say Genetics We Mean.
Based on both of our understandings of
anthropological genetics, we might then define
genetics as the study of the mechanisms of
heredity and biological variation (Stein and
Rowe, Physical Anthropology).
25
The Study of Heredity
Like our considerations of physicality and
anthropology, it is useful to look at some
earlier perspectives on heredity in science.
26
Early Theories of Inheritance
Theophrastus Greek, 4th Century B.C., theories
of germination in plants were applied to human
inheritance. Numerous Greeks believed that
the issue of heredity was based upon the sex that
dominated in the sexual act. Linneaus 18th
century offered a two-layer theory (outer
systems were derived from the father, inner
systems from the mother).
27
Preformation
A popular though sometimes misunderstood notion
of inheritance is given the name preformation.
Beginning with Aristotle and continuing well into
the seventeenth century, preformation assumed
that a human was no more than the unfolding of
that which is already presented in miniature.
The development of preformation as a theory of
inheritance can be attributed, in part, to the
introduction of the microscope in life science
studies in the mid-seventeenth century.
28
Preformation
In its crudest form, the theory assumed that
all organisms of all species, of all of the
generations to come, had been made by God right
at the six days of Creation, and had thus been
encased inside each other, in smaller and smaller
sizes, much in the fashion of a Russian doll.
Thus generation was nothing but the unfolding of
of a pre-existent form from the sexual organs of
the parent. Since sperm cells were discovered
some two decades after the first proposal of this
model, preformationists split into two factions
those who believed that all organisms had
initially been encased inside the egg (the
ovists), and those who held that this role of
mother structure had rather been ascribed to the
sperm (the spermists) (Clara Pinto-Correia).
29
Preformation
30
Preformation
This last quote is from Clara Pinto-Correias
Homunculus Historiographic Misunderstandings of
Preformationist Terminology, in The Ovary of Eve,
University of Chicago Press. This author
makes the point that the term homunculus was
actually not used by preformationists, but it was
ascribed to them later. Preformationists like
Leeuweenoek actually spoke of animalia, figure
animalculorum, and others. Homunculus
actually had an occult/magical connotation and
was not attributed to preformation.
31
Blending Theory
Another such early perspective was blending
theory. Blending theory assumed that the
inherited characteristics of offspring are
intermediate between maternal and paternal
genetic characteristics. Kind of makes sense,
right? Like if you mixed two colors of paint.
The problem is that if blending were the case,
traits would be irreversibly changed from
generation to generation and would not persist.

32
Blending Theory
For example, red paint mixed with white paint
yields pink, but both the red and white colors
cease to exist. Neither the red nor the white
can be reconstituted from the pink.
Red
White
Pink

Red
White
33
Pangenesis
Another early assumption about heredity was
pangenesis. Charles Darwin proposed a mechanism
of heredity whereby he believed that particles
present in the body were influenced by activities
of the organism throughout its life. These
particles traveled to the reproductive cells
through the circulatory system. There they
modified the sex cells in such a way that the
acquired characteristics of the individual
organism could now be passed on to the next
generation.
34
So Whats the Problem?
Well, we know now that human genetics is not a
simple matter that can be explained by simple
factors. Much of the nineteenth-century interest
in the subject revolved around the study of human
characteristics. Human genetics is not that
simple. Further, the experimental method
requires some level of control over the object of
experimentation. No scientist can control human
matings. The study of human genetics must accept
matings that have already occurred. Early
studies of heredity relied on small samples, such
as a family, and such studies relied on the
limited longitudinality of a few generations. It
was impossible for one researcher to study the
inheritance of a particular trait for more than a
few generations.
35
So Whats the Problem?
Yet another problem in the study of genetics is
the selection of the trait to be studied. Many
traits are difficult to measure and quantify.
Until recently, until the invention of
sophisticated instruments, skin color was
difficult to measure. As well, many traits are
affected by the environment (such as skin color
again) and we know that the inheritance of traits
is complex, involving more than one genetic
factor.
36
Enter Gregor Mendel
Beginning in 1865, the Czech monk Gregor Mendel
(1822-1884) first wrote about many of the
principles of heredity. Mendel is famous for his
study of the inheritance of traits in peas. He
realized that the best traits for the study of
heredity were those that were obviously present
or completely absent, rather than those that have
intermediate values and must be measured on some
type of scale.
37
Enter Gregor Mendel
Mendel choose seven contrasting characteristics
of the common pea plant flower color (violet or
white), stature (tall or dwarf), shape of the
ripe seed (smooth or wrinkled) and four others.
38
Enter Gregor Mendel
Using as large a sample as possible to eliminate
chance error, Mendel observed each pea plant
separately and kept the generations apart. The
results were quantified and expressed as ratios.

39
Enter Gregor Mendel
Mendel helped us understand the fallacies of
blending theory. Remember that blending theory
would assume that if you crossed pea plants whose
seeds were yellow with pea plants whose seeds
were green that you would get offspring with
mustard-colored seeds (a combination of yellow
and green). In reality, Mendel discovered that
all offspring had yellow seeds. This discovery
suggested that one trait (yellow seed color)
dominated in its effects.
40
Enter Gregor Mendel
41
Enter Gregor Mendel
When Mendel crossed the plants in this new
generation together, he discovered that some of
the offspring had yellow seeds and some had green
seeds. Somehow the genetic information for the
green seeds had been hidden for a generation and
then appeared again. We call those units of
inheritance genes. The ratio of plants with
yellow to green seeds was nearly 31, suggesting
that a regular process occurred during
inheritance. No matter what trait he selected for
the second generation would show traits at a
ratio of 3 to 1.
42
Mendels Principles of Inheritance
Inherited traits are transmitted by genes which
occur in alternate forms called alleles Principle
of Dominance - when 2 forms of the same gene are
present the dominant allele is expressed Principle
of Segregation - in meiosis two alleles separate
so that each gamete receives only one form of the
gene Principle of Independent Assortment - each
trait is inherited independent of other traits
(chance)
43
Enter Gregor Mendel
The science of genetic inheritance is called
Mendelian genetics.
44
Enter Gregor Mendel
From what is written of Mendels first report on
his studies top the National History Society of
Brünn, no one seemed interested in his research.
In fact, botanists were downright confused by his
work. It is further reported that the audience
to which Mendel offered his findings was hushed,
with no one asking a question of the researcher.
Mendel led out his life doing administrative work
as an abbot of a monastery, unable to find time
for future scientific work. To a person, we can
say that we owe Mendel much. His legacy remains.

45
Modern Evolutionary Theory
As early as 1902, Archibald Garrod took Mendels
findings and found a metabolic disorder known as
alkaptonuria. Garrod found the disorder to be an
example of Mendelian inheritance in humans.

46
What is a Trait?
The observable and measurable characteristics of
an organism is called its phenotype. Whether a
pea or a human being, the phenotype includes,
among other things, physical appearance, internal
anatomy, and physiology.
47
What is a Trait?
In describing the phenotype of a person, we can
observe certain features such as eye color, hair
color, and general body build. We also can
measure such traits as stature, nose width and
arm length. Physiological traits, such as
glucose metabolism, also can be analyzed. The
result of these examinations is a profile of the
individuals total phenotype. A trait is but one
aspect of the phenotype--a particular hair
texture, an allergy, a blood type.
48
The Influence of Environment
The phenotype results from an individuals
genotype and the environment. The genotype
refers to the genetic constitution of the
individual. The environment includes everything
that is external to the individual. A trait can
be the result of the interaction of many genetic
and environmental factors.
49
The Influence of Environment
Many traits are determined solely by heredity
(such as blood type). Other traits are
determined by the environment (a pierced ear or
dyed hair). Most features, however, are
influenced by both genetic and environmental
factors. It is the task of the investigator to
determine the relative influence of genetic and
environmental factors in the development of
specific traits.
50
Molecular Basis of Heredity
All substances are composed of atoms (the
building blocks of matter). Of the 92 kinds of
atoms that occur in nature, 4 are found in great
quantity in living organisms carbon (18.5 of
human body), hydrogen (9.5 of human body),
oxygen (65.0 of human body) and nitrogen (3.3
of human body). Others play extremely important
roles, but are less common. These include
calcium (1.5 of human body), phosphorous (1.0
of human body), sulfur, chlorine, sodium,
magnesium, iron and potassium .
51
Molecular Basis of Heredity
Atoms can join to form molecules (units composed
of two or more atoms linked by a chemical bond),
which can vary tremendously in size depending on
the number of atoms involved. The molecules
found in living organisms are usually of great
size because carbon atoms form long chains that
can consist of hundreds or thousands of atoms and
often include rings of five or six carbon atoms.
Other types of atoms are attached to the carbon
backbone.
52
Molecules of Life
Most of the molecules found in living organisms
fall into four categories carbohydrates, lipids,
proteins, and nucleic acids. The carbohydrates
include the sugars and starches. Lipids include
the fats, oils, and waxes. Some of the most
important molecules of the body are proteins.
Proteins include muscle fibers, enzymes, and
hormones. An understanding of the protein
molecule is essential in comprehending the
action of the genes. Proteins are long chains of
basic units known as amino acids.
53
Molecules of Life
All 20 basic amino acids share a common subunit,
which contains carbon, oxygen, hydrogen, and
nitrogen. Attached to this subunit are various
groups of atoms that define the specific amino
acid. These groups range from single hydrogen
atoms to very complicated groups containing
several carbon atoms, The end of one amino acid
can link up with an end of another, forming a
peptide bond. Short chains of amino acids are
called polypeptides. A protein forms when
several polypeptide chains join together.
54
Molecules of Life
Proteins are further complicated by other bonds.
These bonds can involve sulfur and hydrogen and
can lead to a folding, looping, or coiling of the
protein molecule. The three-dimensional
structure of proteins is important in determining
how they function.
55
The Nucleic Acids
Early in the twentieth century, biologists
debated whether the gene was in fact a protein or
a nucleic acid. It was soon determined that it
was the latter. Nucleic acids are the largest
molecules found in living organisms. Like the
proteins, the nucleic acids are long chains of
basic units. In this case, the basic unit is a
nucleotide. The nucleotide itself is fairly
complex, consisting of three lesser units a
five-carbon sugar, either ribose or deoxyribose
a phosphate unit and a base. The bases fall
into two categories, purines and pyrimidines,
both containing nitrogen. The purine consists of
two connected rings of carbon and nitrogen atoms
the pyrimidine consists of a single ring.

56
The Nucleic Acids

The nucleic acid based upon the sugar ribose is
called ribonucleic acid (RNA). The nucleotides
that make up the RNA contain the following bases
the purines adenine (A) and guanine (G) and the
pyrimidines uracil (U) and cytosine (C). The
nucleic acid based upon the sugar deoxyribose is
called deoxyribonucleic acid (DNA). DNA also
contains adenine, guanine, and cytosine, but in
place of uracil is found the pyrimidine thymine
(T).
57
DNA
Like the rest of the scientific world, physical
anthropology has greatly benefited from the
advances offered by the breakthroughs of genetic
science. At a basic level, physical anthropology
began to understand humans as complex biological
beings, not simply as physical beings. This was
made possible by the discoveries of DNA. At
another more complex level, reflections on the
genetic underpinnings of humans allowed
anthropologists the opportunity to study specific
evolutionary forces operating in individuals and
populations.
58
What is a Gene?
Our bodies are made up of cells, each containing
a nucleus of DNA (Deoxyribonucleic acid). This
huge molecule resembles a sort of spiral ladder,
a double helix whose parts twist and overlap. It
is divided between 23 pairs of complementary
chromosomesone inherited from the father and one
from the mother in each pair. This DNA spiral
contains about three billion bar codes, which
consist of four different basesadenine (A in
red), thymine (T in blue), cytosine (C in green)
and guanine (G in yellow)which are always linked
with each other in the same way as base pairs (A
with T and C with G).
59
What is a Gene?
60
What is a Gene?
About 95 per cent of the DNA in the nucleus has
no known function, while the remaining 5 per cent
contains some 100,000 genes. Pieces of DNA, which
are so minute that they cannot be seen by a
microscope, are composed of several thousands of
bar codes. The way the four base-pairs are
strung together is a sort of coded message by
interpreting this code, and switching particular
genes on and off, the cells manufacture the
proteins which make us what we are.
61
DNA
A molecule known as DNA (deoxyribonucleic acid)
is fairly amazing, to say the least. Imagine
that your whole person--how you look, your
health, how you behave (wellwe might have to
debate this one a bit later) is determined by
this magical molecule inside you! The DNA
molecule provides the codes for biological
structures and the means to translate this code.
We might consider DNA to be a set of instructions
for determining the makeup of biological
organisms.
62
DNA
DNA provides information for building, operating,
and repairing organisms. In this context,
genetic inheritance is seen as the transmission
of this information or the passing on of the
instructions needed for biological structures.
Evolution can be viewed in this context as the
transfer of information from one generation to
the next, along with the possibility that this
information will change.
63
DNA
In 1953, J. D. Watson and E H. C. Crick proposed
a model for the three-dimensional structure of
DNA. DNA consists of two long chains wound around
each other, forming a double helix.
64
DNA
But here is how the double helix model was really
discovered.
65
Alleles
We said that a gene is a section of DNA that has
a specific function. An allele refers to the
alternate form of a gene. The gene for earlobe
type occurs in two forms. We can use the Letter
E to distinguish the two alleles by using the
uppercase E for the dominant allele and the
lowercase e for the recessive allele. E
represents the allele for free-hanging earlobes,
and e represents the allele for attached
earlobes. Recessive refers to the trait that is
not seen in the hybrid, while dominant refers to
the trait that is seen in the hybrid.
66
Alleles
67
Alleles
68
Cell Division
69
Cell Division
The physical basis of Mendelian genetics becomes
clear when we observe the movement of chromosomes
during cell division. There are two basic forms
of cell division, mitosis and meiosis. Mitosis
is the process by which a one-celled organism
divides into two new individuals. In a
multicellular organisms, mitosis results in the
growth and replacement of body cells. Meiosis is
specialized cell division that results in the
production of sex cells or gametes.
70
Genetics into Evolution
Darwin and Wallce articulated key principle of
natural selection found in evolution
Mendel discovered a mechanism for inheritance
One would expect that these would be joined in a
consistent theory of evolution
71
Genetics into Evolution
In fact, this union was not the case. From
1900-1930 geneticists (working with experimental
animals like fruit flies) saw sharp contrasts
within particular characteristics of organisms.
In this perspective, evolution was seen as a
series of large radical jumps (the mutationist
view).
72
The Modern Synthesis
Julian Huxley suggested the modern synthesis
for the perspective that does join the
selectionist and the mutationist perspectives on
evolution. Codified by the mid-twentieth
century, this perspective defines evolution as a
two-stage process (1) Production and
redistribution of variation (inherited
differences among individuals). (2) Natural
selection acts on this variation (inherited
differences, or variation among individuals
differentially affects their ability to reproduce
successfully).
73
Modern Genetic Definition of Evolution
Theodosius Dobzhansky synthesized the mathematics
of the population geneticists and the general
constructs of the theoretical evolutionary
biologists. A modern definition of evolution
suggests it as change in gene frequency from one
generation to the next.
74
Hardy-Weinberg
75
Hardy-Weinberg Equilibrium
The Hardy-Weinberg Law applies to closed
population in which all individuals of one
generation have descended from parents who were
members of the same population. This condition
is rarely met in natural populations because
individuals often move between populations. As
individuals move from one population to another,
they carry their genes with them and potentially
change the gene and genotypic frequencies in the
new population.
76
Genetics and Behavior
Our second chapter closes with the question of
the extent to which behavior is governed by
genetic forces.
77
Genetics and Behavior
This significant question leads us to reflecting
on the nature/nurture debate. Is our behavior
caused by our genes (nature) or by the physical
and cultural environment (nurture)? As our
chapter indicates, from the late 1800s through
the early 1900s the prevailing view was that
nature was the culprit, with a shift to nurture
beginning in the 1930s. So which is it?
78
Genetics and Behavior
Anthropologists would argue for the bicultural
view of humans and would suggest that both nature
and nurture impact our behavior and our worlds.
Anthropologists would not want to be
deterministic and attribute complex behaviors to
one causal factor. Anthropologists often
approach their studies by looking for
multi-causality rather than mono-causality.
Genetics and environment often work together and
play off one another. As Goulds example from
the chapter suggests, certain forms of human
nearsightedness are due entirely to inheritance,
but they can nonetheless be corrected by glasses
(57).
79
Chapter 3 Principles of Microevolution
80
Population Genetics
In the midst of the selectionist/mutationist
debate, population genetics emerged. Its
specific focus drew on a focus of mathematic
reconstructions of evolution--in particular the
measurement of small accumulations of genetic
changes in populations over just a few
generations. Figures in the field included
Ronald Fisher (The Essential Theory of Natural
Selection, 1930), Sewall Wright, JBS Haldane and
Sergei Chetverikov.
81
Definitions of Population
The term breeding population is frequently used
in evolutionary theory. In an abstract sense,
the term breeding population means a group of
organisms that tend to choose mates from within
the group.
82
Evolutionary Forces
83
Changes in Allele Frequency
Forces that cause change Mutation Genetic
Drift Founder Effect Bottleneck
Migration Non-Random Mating
84
Mutation
An actual alteration in genetic material is
called mutation. A genetic trait may take one of
several alternate forms, which we have defined as
alleles. If one allele changes to another--that
is, if the gene itself is altered--a mutation has
occurred. As we can see, a mutation is a
molecular alteration--a change in the base
sequence of DNA. For such changes to have
evolutionary significance, they must occur in sex
cells, which are passed between generations.
Evolution is a change in gene frequencies between
generations. If mutations do not occur in sex
cells no evolutionary change can result.
85
Mutation
It would be rare to see evolution occurring by
mutation alone. Mutation rates for any given
trait are quite low, and thus their effects would
rarely be seen in a small population. In larger
populations, mutations might be observed, but
would, by themselves, have very little impact on
shifting gene frequencies. However, when
mutation is coupled with natural selection,
evolutionary changes are quite possible.
Mutation is the very basic creative force in
evolution, and in fact is the only way to produce
new variation. Its key role in the production
of variation represents the first stage of the
evolutionary process. Darwin was not aware of
the nature of mutation only did twentieth
century genetic advancements bring out the nature
of mutation.
86
Mutation
The movement of genes from one population to
another is called migration. If all individuals
in a given population do not choose their mates
from within the group, significant changes in
gene frequencies could occur. If a change in
gene frequency does take place, evolution will
have occurred, this time by migration. In
humans, social rules, more than any other factor,
determine mating patterns and cultural
anthropologists often work with physical
anthropologists to isolate and measure this
important evolutionary force.
87
Genetic Drift
Genetic Drift is..a new band?
88
Genetic Drift
Genetic Drift is..a role-playing game?
89
Genetic Drift
Actually.the random force in evolution is called
genetic drift. It is primarily due to sampling
error. Since evolution occurs in populations, it
is directly tied not only to the nature of the
initial gene frequencies of the population, but
to the size of the group as well.
90
Genetic Drift
The Hardy-Weinberg Law assumes that populations
are of infinite size. Therefore, there is no
variation resulting from the process of sampling
gametes which will produce the next generation.
Genotypic frequencies remain constant from
generation to generation because gene frequencies
represent representative samples of frequencies
in the prior generation. Populations, however,
are of finite size. Because of sampling error
(variation due to chance events in the sampling
process), a set of gametes drawn from a parental
population will rarely, if ever, have exactly the
same gene frequency as the parental population.
Thus, in all populations there are some chance
fluctuations in gene and genotype frequencies
from generation to generation.
91
Genetic Drift
92
Genetic Drift
Genetic drift illustrates that chance effect can
cause a change in allele frequency. For example,
a chance event can cause massive death. Survival
may be totally unrelated to genotype. This
contradicts Darwins notion of the survival of
the fittest.
93
Genetic Drift
Founder Effect A type of genetic drift caused by
the formation of a new population by a small
number of individuals. Bottleneck Effect A
severe reduction in population size may have
similar genetic consequences as the Founder
Effect.
94
Gene Flow
Gene flow refers to the movement of individuals
between populations. It moves the alleles
carried by individuals. It can alter the allele
frequency in both populations and can be a chance
event, unrelated to genotype.
95
Natural Selection Acts on Variation
The evolutionary forces described act to produce
variation and to distribute genes within and
between populations. But there is no long-term
direction to any of these factors. What then
does enable populations to adapt to changing
environments? The answer is natural selection.
Given that there is genetic variation among
individuals within a population, some of these
variations may influence reproductive success
(numbers of offspring successfully raised). If,
as a result of genetic variation, some
individuals contribute more offspring to
succeeding generations, this is natural
selection. In fact, we may define natural
selection as differential net reproductive
success.
96
Adaptation in Populations
How then do populations adapt? A result of
natural selection is a change in gene frequency
relative to specific environmental factors. If
the environment changes, then the selection
pressures changes as well. Such a functional
shift in gene frequencies is what we mean by
adaptation. If there are long-term environmental
changes in a consistent direction, then gene
frequencies should also shift gradually each
generation. If sustained for many generations,
the results may be quite dramatic.
97
Interaction of Evolutionary Forces
98
Modern GeneticsControversies and Possibilities
x
99
Modern GeneticsControversies and Possibilities
There are several methods of cloning. But until
the birth of the cloned sheep, Dolly, in July
1996, it was necessary to use test-tube embryos
derived from an encounter between an egg and a
spermatozoid. The embryos were divided in two and
each half implanted inside a surrogate mother to
obtain two clones. The creation of Dolly was
revolutionary because it did not require using a
normal embryo (one made by an egg and a sperm).
The famous sheep of the 1990s was born from the
marriage of an egg cell from which the nucleus
had been removed and an adult cell taken from the
sheep to be cloned.
100
Modern GeneticsControversies and Possibilities
101
Modern GeneticsControversies and Possibilities
Genetically engineered crops
102
Modern GeneticsControversies and Possibilities
Genetic Counseling--the advising of prospective
parents or a person affected by a genetic disease
of the possibility of having a child with a
genetic problem. Abnormality Identification--comm
only through observation of the fetus through
ultrasound or other technologies.
103
Modern GeneticsControversies and Possibilities
Genetic Engineering--includes a number of
possibilities in which genetic material is
altered to create specific characteristics in
individuals. Includes Regulatory
Genes--turning a gene on or off in the case of
the faulty action of a regulatory gene.
Restriction Enzymes--can be used to cut the DNA
at specific sites. Artificial Genes--an
artificial gene is used to replace a defective
gene. Cloning--the process of producing a group
of genes, cells or whole organisms that have the
same genetic constitution.
104
Modern GeneticsControversies and Possibilities
Gene Therapy--involves detecting a genetic defect
and correcting it by replacing the DNA sequence
that causes the defect with the correct DNA
sequence.
105
Conclusion