Human Genetics
I.
Chromosomes
A. Human genome is comprised of 23 pairs of
chromosome
B. Sex chromosomes – the 23rd pair of
chromosomes determine gender (male or female)
1. Females have X and X
2. Males have X and a small Y
 The gender of the baby is always
determined by?
C. Autosomes – the remaining 22 pairs are non-sex
chromosomes
D. Karyotyping - Cell biologists take photographs of
cells in mitosis when the chromosomes are easy to
see
II. Human Traits
A. Geneticists study how a trait is passed from one
generation to the next
B. Genetics versus Environment
1. Many traits are strongly influenced by
environmental factors, such as nutrition and
exercise
(Ex: average height in 1800s in Europe was 10
cm shorter than today due to poor nutrition)
2. Genes that are denied the proper environment
may not reach full expression
(Ex: alcoholism is influenced by your genetics,
but if you don’t drink you can’t become an
alcoholic)
C. Pedigree chart
1. Shows the relationships within a family for single
gene traits
2. Genetic counselors analyze pedigree charts to
figure out genotypes of family members
3. How to read a Pedigree chart:
LABEL THIS PEDIGREE CHART
Circle = female
Horizontal line
= a couple
Square = male
Vertical line and a
bracket connect the
parents and children.
Half-shaded =
person is a carrier
Completely shaded
= person expresses
the recessive trait
Not shaded =
person does
not
expresses
the trait nor
is a carrier
a. Determine which individuals are carriers for
albinism (half shade the circles and squares).
b. Is albinism dominant or recessive?
III. Human Genes
A. Biologists have identified some genes that control a
single human trait
1. Blood type genes (multiple alleles)
Blood Type
Genotype
Surface Protein
Antibodies**
A
AA or AO
A
b
B
BB or BO
B
a
AB
AB
A&B
O
OO
--
-a&b
**The antibodies are only produced when the recipient is
exposed to the wrong surface proteins.
IV. Genetic Disorders
A. Recessive Autosomal Disorders - diseases caused by
genes on chromosomes #1-22 where both alleles are
recessive for the trait
1. Albinism – lack of pigment in hair, skin, and eyes
2. Cystic fibrosis – mutation on chromosome 7 that
causes excess mucus in lungs, digestive tract and liver,
and increased infection; patients die by drowning on
own mucus. More common in people of Northern
European descent
Chromosome # 7
CFTR gene
Abnormal CFTR
proteins cannot
transport Cl- across cell
membranes.
Cells in the person’s airways
become clogged with a thick
mucus.
3. Tay-Sachs disease
a. Deadly lipid storage disorder
b. Caused by defective enzyme that prevents normal
formation of the brain causing mental retardation,
blindness and early death
c. Affects central and eastern European Jewish populations
4. Sickle cell anemia
a. Abnormal form of hemoglobin causes red blood cells to be
sickle shaped
b. Sickle cells get stuck in capillaries resulting in damage to
brain, heart, and spleen
c. Affects 1 in 500 African Americans
Why are most disorders due to recessive alleles?
Why are these recessive genetic disorders primarily found in
African and Jewish populations?
B. Dominant Autosomal Disorders
1. Achondronplasia – dwarfism
2. Huntington’s disease – mental deterioration and
uncontrollable movements; usually occurs in
middle age
 If everyone with Huntington’s allele dies, how does the
disease continue?
 If one of your parents has the disease what are the chances of
you getting the disease?
Parents Genotypes
Hh and hh
H h
h Hh hh
h Hh hh
50%
Chance
C.
Sex-linked disorders - these genes are found on
the X chromosome.
1. Color blindness – 1 in 10 males; 1 in 100
females
2. Hemophilia – lack blood clotting protein;
affects 1 in 10,000 males
 Why are sex linked disorders more common
in males?
D. Chromosomal Disorders
1. Most common are non-disjunction, which is the
failure of chromosomes to separate during
meiosis, resulting in daughter cells with an
abnormal number of chromosomes
3. Turner’s Syndrome
a. Females missing one of the X chromosomes (0 X)
b. Sterile and very short but have normal
intelligence.
4. Klinefelter’s Syndrome
a. Males with an extra X chromosome (X X Y).
b. Sterile and can have several female
characteristics
5. Down Syndrome
a. Have extra twenty first chromosome
b. Common in children of mothers over 40
c. Dwarfs, mentally retarded and usually have
heart problems.
V.
Human Molecular Genetics
A. DNA analysis
1. Testing for alleles
a. Parents can get a genetic test for hundreds of
disorders (e.g. Tay-Sachs, CF)
b. Scientists look for differences in DNA sequence
on specific genes
2. DNA fingerprinting
a. Analyzes sections of DNA that are believed to
have little to no function
b. Highly varied from human to human
c. Used to convict criminals and free wrongly
convicted
3. Amniocentesis
a. Involves removing some fluid from the woman’s
womb then conducting genetic tests on it.
B. Gene Therapy
1. An absent or faulty gene is replaced by a
normal working gene
2. Body is then able to make the correct protein,
eliminating the disorder
3. Modified viruses are sometimes used to insert
the corrected gene into human cells
Bone marrow cell
Normal hemoglobin gene
Nucleus
Chromosomes
Genetically
engineered virus
Bone marrow
Gene Therapy Movie