Transcript Human Genetics PPT

Human Genetics
By: K Marsh
Genetics Vocabulary
Go Over Quick Genetics Review
Genotype- the two alleles in an organism
Phenotype- outward appearance of an
organism
Allele- when there is more than one type of
expression for a gene (ie humans have a
freckles allele and a no freckles allele).
The Madness of King George III
 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. These included 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
thought to have a genetic basis
 Acute intermittent porphyria seems to be consistent with the
symptoms exhibited by George III
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
 Because we are talking about how humans are when we are
talking about human genetics, there can be lots of
controversy when traits are 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
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
Having a bent little finger is a dominant trait
Dominant/Recessive Human Traits
Albinism - There are a number of different types of
albinism, but each is characterized by an absence of
pigment from the skin, eyes and hair. Albino individuals
typically have very pale white skin, light blue or pink
eyes, and light blond or white hair. Albinism is a
recessive trait. Some albanism is related to pleiotropy
(will be discussed later).
Brown teeth - Teeth have a brown color that is not the
result of poor oral hygiene or antibiotics taken as a child.
White teeth are dominant.
Dominant/Recessive Human Traits
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.
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
Hand folding - When the hands are folded either the left
or right thumb will be on top. Left thumb on top is
dominant.
Mid-digital hair - Hair growing from the middle section
of each finger. Hair presence is dominant.
PTC tasting - Phenylthiocarbamide (PTC) is a bitter
tasting chemical that cannot be tasted by some
individuals. PTC tasters taste PTC as bitter, non-tasters
taste nothing when given PTC. Tasting is dominant to the
inability to taste PTC.
Dominant/Recessive Human Traits
Tongue rolling - Tongue rolling is the ability to form a
tube with your tongue. Rolling is dominant.
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.
Specific Human Traits
Dimples - Round indentations in the cheeks when
smiling, not lines or clefts.
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.
Hair whorling - These may be referred to as cowlicks.
Areas in which hair grows from your scalp in a whorl
instead of in a given direction.
Specific Human Traits
Myopia - Short sightedness, the inability to see far off
objects without correction by glasses or contacts is a
recessive trait.
Polydactyly - Having more than five digits on each hand
and foot is a dominant trait.
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.
Beyond Simple Genetics
Polygenic
Pleiotropy
Sex-Linked
Co-dominance
Incomplete Dominance
Multiple Alleles
Polygenic
Human Skin Color
Polygenic inheritance is a pattern responsible
for many features that seem simple on the
surface. Many traits such as height, shape,
weight, color, and metabolic rate are governed
by the cumulative effects of many genes.
8 different genes code for melanin and skin
pigmentation
Polygenic
 Eye color is determined by more than
one gene
 Thus eye color appears to vary on an
almost continuous scale from brown to
green to gray to blue
 Eye color is determined by two genes,
one controls texture of the iris which
refracts light to make blue. A second
determines relative abundance of
melanin. When a small amount of
melanin is present, green eyes result
while brown and black eyes result from
relatively increasing amounts of melanin
Polygenic
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
Pleiotropy
Pleiotropy occurs when a single gene
influences multiple phenotypic traits.
Sickle-cell anemia, is an example. A single
gene results in irregularly shaped red blood
cells that painfully block blood vessels, cause
poor overall physical development, as well as
related heart, lung, kidney, and eye problems.
Sex Influenced Human Traits
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, but carried on an
autosome
Index finger shorter than ring finger - The index finger
(next to your thumb) is longer than the ring finger (next to
your little finger).
Sex Linked Human Traits
Color blindness - Inability to distinguish between colors
of the same intensity. There may be two types, red green
color blindness in which individuals perceive red and
green as the same color, and complete color blindness in
which all colors are perceived as being the same and
vision is the functional equivalent of black and white
television. Both types of colorblindness are sex linked
traits.
Co-Dominance
Two or more alleles are dominant, they
both express their traits phenotypically.
Examples:
Dalmations, Holstein Cows, & Zebras. Both
black and white colors are shown at the same
time.
Incomplete Dominance
Neither allele in a genotype is fully
expressed, there is a blending of both
traits.
Example:
A pink carnation flower is created from parents
that are white and red for flower color.
Multiple Alleles
Multiple alleles are when there are three or
more alleles for a given trait (gene).
Example:
Blood Types: There are A, B, and O blood types.
Hand out Blood typing permission slips.