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Species – Genetic Variation
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Main Points for Class Meeting:
1.
What is a Species?
2.
What makes species different from each
other?
3.
What are the sources of variation within
species?
1. What is a Species?
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Species : Latin for “kind” or
“appearance”
Morphological differences used to
distinguish species
Differences in body function,
biochemistry, behavior, and genetic
makeup also used
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The Biological species concept
Species:
A population whose members can interbreed
under natural conditions to produce
healthy, fertile offspring, but cannot
produce healthy, fertile offspring with
members of other species.
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Species are based on infertility, not physical
similarity.
Eastern and western meadowlarks have
similar shapes and coloration, but differences
in song help prevent interbreeding between
the two species.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Species are based on infertility, not physical
similarity.
In contrast, humans have
considerable diversity,
but we all belong to the
same species because of
our capacity to
interbreed.
2. What makes species
different from each other?
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Genes!
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Where are genes found?
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On Chromosomes!
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Chromosomes are
made of condensed
DNA
Here is a complete
set of Human
chromosomes:
Different species have different
numbers of chromosomes:
Species:
Number of
Chromosomes:
Mosquito
Guinea pig
Yeast
Cat
Humans
Dog
6
16
32
38
46
78!
Different species have different
numbers of chromosomes:
Species:
Number of
Chromosomes:
Mosquito
Guinea pig
Yeast
Cat
Humans
Dog
6
16
32
38
46
78!
Half of an individual’s
chromosomes come from its
mother, & half from its father
If the chromosomes from the 2
parents don’t “match,” then the
2 parents are NOT the same
species
Then what happens?
• No offspring can be produced
• OR the offspring are infertile
Example?
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The MULE:
Mules are a hybrid
between a horse & a
donkey – 2 closely
related species
3. What are the sources of
variation within species?
Genetic Diversity –
combinations of different
forms of genes!
Genes are located on
Chromosomes
Some genes have 2 (or more)
forms, called “alleles”
Offspring can inherit 1 form of the gene
from one parent, and another form from
the other parent.
Human Genetics
Modified from a presentation by
Timothy G. Standish, Ph. D.
http://www.grisda.org/tstandish/teachers/presentations/General%20Biology/Human%20Ge
netics.ppt#1
The Madness of King George III
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Partly as a result of the erratic behavior of King
George III the American colonies decided to break
away from the United Kingdom
Other members of King George’s family also
exhibited strange behavior with dire consequences:
Mary Queen of Scots and her son James I both of
whom were beheaded.
Because madness seems to have run in the family, it is
thought to have a genetic basis (“acute intermittent
porphyria”)
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Human Heredity Is Not
Unique
The genes of humans behave in the same way as
genes of other organisms
Of the estimated 100,000 human genes, most are
identical in all humans
The relatively small number of “polymorphic”
genes in humans account for only part of the
variability that we see between humans
While each human (except for identical twins) has
a unique set of genetic information, variation
between humans also results from differences in
the environment
Politics and Genetics
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Human genetics: how humans are - can lead to
controversy when traits seen as relating to race, gender
or other sensitive issues
This is particularly true when we start to talk about the
genetics of behavior
Nazis and other extreme right wing politicians see
human worth and behavior being based on genetics
Communists and other extreme leftwing politicians
see humans as infinitely pliable and molded by their
environment not genetics
Simple Dominant/Recessive Traits
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Many human genes are inherited as dominant or
recessive traits (just like the traits Mendel studied
in peas)
Ear lobes provide an example of this:
Unattached
ear lobes are
inherited as a
dominant
trait.
Attached ear
lobes are
inherited as a
recessive
trait.
Simple Dominant/Recessive Traits
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Having a bent little finger is a dominant trait
Dominant/Recessive Human Traits
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Cleft chin - A noticeable indentation at the center
of the chin. For examples think of Kirk Douglas
and Michael Jackson (after plastic surgery).
Having a cleft chin is dominant to a smooth chin.
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Double-jointed thumbs - This is commonly
called a hitchhiker's thumb. The thumb can bend
back at almost 90 degrees. Hitchhiker's thumb is a
recessive trait, but it may vary in its expression.
Dominant/Recessive Human Traits
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Hand folding - When the hands are folded either
the left or right thumb will be on top. Left thumb
on top is dominant.
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Mid-digital hair - Hair growing from the middle
section of each finger. Hair presence is dominant.
Dominant/Recessive Human Traits
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Tongue rolling - Tongue rolling is the ability to
form a tube with your tongue. Rolling is
dominant.
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Widow's peak - A sharp point in the hairline that
points toward the nose. Having a widow's peak is
dominant to a smooth hairline.
Sex Influenced Human Traits
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Baldness - Loss of hair from the scalp following
puberty. A sex influenced trait that is most
commonly fully expressed (as a dominant trait) in
males
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Index finger shorter than ring finger - The
index finger (next to your thumb) is longer than
the ring finger (next to your little finger). Check
the class data to see if the frequency is different
for the different sexes.
Sex Linked Human Traits
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Color blindness - Inability to distinguish between
colors of the same intensity. There are two types:
red-green color blindness, and complete color
blindness. Both types of colorblindness are sex
linked traits.
Specific Human Traits
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Freckles - Small patches of darker pigmented skin
on various parts of the body and most visible in
those areas commonly exposed to the sun. These
may be present on both dark and light skinned
individuals.
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Polydactyly - Having more than five digits on
each hand and foot.
Specific Human Traits
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S-methyl thioester smeller - S-methyl thioesters
are produced in the urine after consumption of
asparagus. Some individuals cannot smell this
substance. If you smell a strong odor on urination
after eating at least 5 asparagas spears, you are an
S-methyl thioester smeller.
Multiple Alleles
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Eye color varies on an almost
continuous scale from brown to
green to gray to blue
Eye color determined by two
genes:
 one controls texture of the iris
which refracts light to make
blue;
 second determines relative
abundance of melanin: small
amount of melanin = green
eyes, increasing amounts of
melanin = brown and black eyes
Multiple Alleles
Hair color is determined by
more than one gene
 Thus hair color appears to
vary on an almost
continuous scale from black
to brown to blond to red
 The brown and black
pigment is melanin
 The red pigment is an iron
containing molecule
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Genetic Diversity
Key Questions:

1.
Relationship between species diversity & genetic
diversity
2.
What is the hierarchy of concepts that connect
species to genes (& DNA)?
3.
What is the importance of genetic variation?