Vocabulary 1. genome
2. karyotype
3. sex chromosome
4. autosome
5. pedigree chart
6. sex-linked gene
7. nondisjunction
8. DNA fingerprinting
9. Human Genome Project
10.gene therapy
I. Human Heredity A. Human Chromosomes
1. Karyotype = set of photographs of chromosomes grouped in order in homologous pairs
2. Sex chromosomes = 23rd pair of chromosomes determines sex (females XX, males XY)
3. Autosomes = remaining 44 chromosomes that are not sex chromosomes
B. Human Traits
1. Pedigree chart = shows the relationships within
a family for single gene traits
2. Genetic counselors analyze pedigree charts to
figure out genotypes of family members
3. Genetics vs. Environment
a. Many traits are strongly influenced by
environmental factors, such as nutrition
and exercise
b. Genes that are denied the proper
environment may not reach full
expression
1) Ex: average height in 1800s in Europe was 10
cm shorter than today due to poor nutrition
2) Ex: susceptibility to alcoholism is influenced
by your genetics
Circle = female Square = male
Horizontal line =
a couple
Vertical line and
a bracket
connect the
parents and
children.
Half-shaded =
person is a carrier
Completely shaded
circle or square =
person expresses
the trait
Not shaded =
person
neither
expresses
the trait nor
is a carrier
4. How to read a pedigree chart
DRAW
5. Ex: Albinism
pedigree chart
DRAW &
Complete
Determine which individuals are carriers for
albinism (half shade the circles and squares).
Figure out the genotypes for each individual on the
chart.
D. Autosomal disorders
1. Recessive allele disorders a. Tay-Sachs - nervous system breakdown and death
in 1st few years of life
b. Albinism – lack of pigment in skin, hair, eyes
c. Cystic fibrosis – excess mucus causing increased
susceptibility to infection Chromosome # 7
CFTR gene
Missing 3 DNA
bases,
phenylalanine is
missing from the
CFTR protein.
Abnormal CFTR
proteins cannot
transport Cl- across cell
membranes.
Cells in the person’s
airways become clogged
with a thick mucus.
2. Dominant allele
disorders
a. Dwarfism – disorder
of bone growth; 1 in
40,000 births
b. Huntington’s
disease – loss of
muscle control and
mental functioning
until death,
symptoms appear
over 30 years old
3. Codominance disorders
a. Sickle cell anemia
1) common among those of
African descent
2) twisted red blood cell or
“sickle” gets stuck in
capillaries resulting in
damage to brain and
heart
3) Why does this disease
persist? -- those
heterozygous for sickle
cell anemia are more
resistant to malaria
Malaria
Sickle cell
II. Human Chromosomes A. Genes make up only about 2-5% of
chromosomes (the rest doesn’t seem to
code for anything that we know of right
now)
B. Sex-linked genes = genes located on the
X or Y chromosome
1. >100 sex-linked disorders are located on the
X (X is much larger than Y)
2. X-linked alleles are always expressed in
males since they have only one X
chromosome
3. Colorblindness
a. Red-green colorblindness is found in 1
out of 10 males in the U.S.
4. Hemophilia a. Recessive allele causes no protein for
blood clotting, bleed to death from minor cuts
b. 1 in 10,000 males affected
5. Muscular Dystrophy a. Weakening and loss of skeletal muscle
b. 1 in 3,000 males affected
C. X-chromosome inactivation 1. If one X chromosome is enough for a male,
how does the cell adjust to the extra X in females?
2. In females, one X is randomly switched off.
3. Ex: In female cats, one X chromosome is switched off in different areas of the body resulting in two different colored spots (calico).
Tortoiseshell cat Calico cat
D. Chromosomal Disorders 1. Nondisjunction = most common error in meiosis
occurs when homologous chromosomes fail to
separate
2. Nondisjunction results in an abnormal # of
chromosomes ending up in a sex cell
3. Down syndrome
a. 3 copies of chromosome 21
b. Results in mild to severe mental retardation
c. 1 in 800 babies born in the U.S. have Down
syndrome
Homologous
chromosomes fail to
separate
Meiosis I:
Nondisjunction Meiosis II
E. Sex chromosome disorders 1. Turner syndrome – XO, female inherits
only one X
a. 1 in 2,500 females
b. Sterile, sex organs do not develop at puberty
2. Klinefelter syndrome – XXY, an extra X
a. 1 in 500 to 1,000 males
b. Usually sterile, often male sex organs and breasts develop
c. No instances of YO, so X chromosome contains info. necessary for survival of embryo
III. Human Molecular Genetics A. Human DNA Analysis
1. Testing for Alleles a. If 2 prospective parents suspect that they might
carry a recessive allele for a genetic disorder, they can ask for a genetic test
b. Genetic tests are available for 100s of disorders
2. DNA fingerprinting a. Analyzes sections of genes that vary widely
between individuals
b. Get from samples of blood, hair, semen, and skin
c. High reliability - DNA fingerprinting is used in the justice system
B. The Human Genome Project 1. Began in 1990 and finished in 2000
2. an ongoing effort to analyze the human genome sequence
3. Worldwide we are searching for genes that may provide useful info. for understanding traits and to develop new drugs and treatments
4. Discoveries on the human genome is public info. and new info. can be found online
C. Gene Therapy
1. An absent or faulty gene is replaced by a normal,
working gene
2. Viruses are used to insert the corrected DNA into a
cell’s DNA (virus is modified to not cause disease)
3. Gene therapy treatments are high risk and not
always successful; procedure is still considered
experimental
Normal hemoglobin
gene
Bone marrow cell
Chromosomes
Genetically engineered virus
Nucleus
Bone
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