Download Human Heredity

Human Heredity
Who and What and Why of Humans?
New Flash……..
It has been discovered that having a glowing “red nose”
is a recessive sex-linked trait in Reindeer….. AND….the
strange ability to fly is also a recessive autosomal trait…..
Deep within the Taiga, two adult consenting Reindeer
mate…… the male is homozygous recessive and thus has
the ability to “fly”…. But has a normal black nose………
The female is a sex linked carrier for “red glowing
nose”…but her phenotype is black nose….and she is
heterozygous for flying ability….thus cannot fly……
Can these two Reindeer create Rudolph??
What about Rudolpha??
SHOW YOUR WORK…..
Key, parents, gametes, Punnett square, results…….
Dominant Genes in Humans
• Simple Dominant Traits (A)
– -Huntington’s disorder
– Free hanging earlobes =
dominant
– Polydactyly (more than
five digits) = dominant
– -Right handed over left
handed
Huntington’s Disease –
Dominant Gene
A lethal disease caused by
A rare dominant gene.
– Nervous system degenerates.
» Uncontrolled, jerky movements
• No treatment • Onset occurs in the thirties so they could have
passed it on to their children• 1 in 10,000
Recessive Genes in Humans (a)
• Cystic Fibrosis - the most common lethal
genetic disorder among white Americans.
– 1 in 25 white Americans carries it. (Aa)
– The mucus in the lungs is particularly
thick.
– Breathing is difficult because mucus
collects in the lungs.
Recessive Genes in Humans (b)
• Sickle-cell anemia - most
common recessive gene
found in African Americans.
– 1 in 500 African Americans is a
carrier (Bb)
– Red blood cells are sickle
shaped.
– The red cells cannot carry
oxygen as well when sickled.
– Cells can clog the blood vessels.
– Does decrease the chances of
malaria infection
Recessive Genes in Humans (f)
• Tay-Sachs Disease - is a disease to the central
nervous system.
• Occurs in the Jewish population. (Ff)
–
–
–
–
Lipids ( fat ) are broken down by an enzyme.
People with Tay-Sachs do not produce this enzyme.
Lipids (fats) build up in the brain .
And results are a loss of movement, blindness and
mental deterioration.
– Death occurs before the age of five. ( ff )
Multiple Alleles ( A, B , O)
• Blood Groups - blood types are determined by
three different alleles- A, B, O
– The Blood gene (I) has three different alleles
• A = A blood - A surface molecule
Both codominant
• B = B blood - B surface molecule
• O = O blood - no surface molecule - recessive
Genotype
Phenotype
IA IA IAi
A Blood
IBi
B Blood
O Blood
IB IB
i i
Genotype Phenotype
IA IB
AB Blood
Polygenic Traits
• There are thousands of traits in humans in where
many genes ( polygenic ) combine to form one
trait.
• As many as 12 or more genes acting together to
produce…..
–
–
–
–
Eye color
hair color
skin color
Foot size
Sex-Linked Traits
• Males are XY
• Females are XX
• The Y chromosome does not have the genes to
mask the genes that are on the X chromosome
• Examples are
– Red Green Color Blindness
– Hemophilia
Red - Green Color Blindness
• People with red-green
color blindness can not
see the difference
between these two colors
Female Carrier
XR
Xr
XR XR XR XR Xr
Y
XR Y Xr Y
Hemophilia
• Hemophilia is a sex-linked disease in which
a person is unable to clot their blood when
they cut or bruise themselves.
• The family of Queen Victoria is best known
Female Carrier
for this disease.
H
h
Male Normal
X
XH
Y
X
XH XH XH Xh
Female Normal Female Carrier
XH Y
Xh Y
Male Normal Male Hemophiliac
What determines the sex of the
offspring???
• The 23rd pair of chromosomes are called the
sex chromosomes.
• In the male , they are X and Y
• In the female they are X and X
•
X Y
• X
• X
Mistakes in Meiosis
• In meiosis there is a
chance that some pairs of
chromosomes will not
split.
– This causes the chance
of Trisomy
– ( 3 chromosomes of a
certain chromosome )
– Karyotype is a picture
of all the chromosomes.
– It is determined by
Amniocentesis, a
sample of amniotic
fluid from the uterus
Nondisjunction
• The failure of a
chromosome pair to
separate during meiosis.
• Down’s Syndrome is a
disorder where no
separation of the pair
chromosome 21.
– This causes the sperm or
egg to carry 24
chromosomes.
– Occurs in a higher amount
to mothers over 40
– Also called
–
Trisomy 21
3 chromosome 21’s