Chapter 19: Human Genetics
19.1 Chromosomal Inheritance
Objectives: Explain the normal
____________________ inheritance of
humans. Describe how a karyotype is prepared
and two ways to obtain ________________
chromosomes. Explain how nondisjunction
results in inheritance of an abnormal
chromosome number. Describe Down
syndrome and various syndromes that result
from the inheritance of an abnormal sex
chromosome number.
Biology Review:
- Humans have ____________ pairs of
chromosomes, total 46.
- First 22 pairs are called autosomes (self)
- Final pair is sex chromosomes and determine
the gender.
*Males are _______ and females are
____________.
- Disorders in humans results from the wrong
number of chromosomes or from problems in
an individual chromosome.
- Syndrome: group of
____________________________ that always
occur together.
- __________________________: a display of
the chromosomes arranged, by size, shape, and
banding pattern.
* Can reveal if a person has too many copies
of chromosomes, too few copies of
chromosomes, or if the length of a specific
chromosome is abnormal.
I. Karyotyping
A. What can be used for karyotyping?
1. Anything but RBCs…why?
__________________________________
2. Easiest: ___________________________
that are separated from the blood.
B. Fetal Karyotyping
1. Amniocentesis
a. A long __________________ is used to
withdraw amniotic fluid containing fetal cells
b. Increases risk of spontaneous
___________________________ by 0.3%
2. Chorionic Villi Sampling (CVS)
a. A tube is used to remove cells from the
chorion, where the _____________________a
will develop.
b. Greater risk of spontaneous abortion: 0.8%
C. Blood Tests
1. Blood tests may indicate a need for
chromosomal studies.
2. Measures the levels of four chemicals in the
blood
a. alpha-fetoprotein: produced by fetal liver
b. estrogen-like hormone produced by
placenta
c. human chorionic gonadotropin: pregnancy
hormone
d. Inhibin-A: hormones produced by the
fetus and placenta.
* Abnormal highs and lows of these are
linked to certain chromosomal and structural
abnormalities
* Amnio and CVS can confirm the
abnormality
D. Preparing a Karyotype
1. Place cells in culture medium to stimulate
__________________________.
2. Specific chemical used to stop mitosis at
_____________________ when the
chromosomes are condensed.
3. Cell spread on microscope slide and dried.
4. Then __________________________.
5. Photographed.
6. The staining allows light and dark bands
that help pair them up.
II. Nondisjunction
A. Occurs during _________________ when
both members of a homologous pair go into
the same daughter cell.
B. Or, during meiosis II when the sister
chromatids fail to separate and both daughter
chromosomes go into the same gamete.
C. Trisomy: One
____________________chromosome. Total
count is 47 chromosomes instead of 46.
D Monosomy: One type of chromosome is
present in a ___________________ copy.
Total count is 45.
E. Down Syndrome
1. Trisomy ________________.
2. Rounded heads
3. Short, webbed neck
4. Eyes that slant upward and have an inner
eyelid fold
5. Risk increases at age 40.
a. before 40, one in __________
b. after 40, one in _________________
6. Amniocentesis followed by karyotyping
necessary to confirm.
III. Sex chromosome inheritance
A. Women are XX, men are XY.
1. Gender is determined by
_________________________.
B. Too Many/Too Few Sex Chromosomes
1. Turner Syndrome (XO)
a. short, broad chest, webbed neck
b. infertile, no breasts
2. Klinefelter syndrome: XXY
a. sterile
b. testes and prostate gland are
underdeveloped, no facial hair
3. Poly-X syndrome
a. Tend to be tall and thin, most are not
mentally retarded
b. fertile, and normally regular karyotype
4. Jacobs syndrome: XYY
a. When does this nondisjunction occur?
b. persistent acne, tend to have reading and
speech problems, tall
5. YO males…not viable
19.2 Genetic Inheritance
Objectives: Explain the autosomal
_______________________ and recessive allele
inheritance. Explain X-linked inheritance and why
males have more X-linked disorders than females.
Relate the inheritance of an allele to protein synthesis.
Tell how a genetic counselor could help a couple who
are carriers for cystic fibrosis.
Review:
- Genes: section of chromosome that codes for a
specific ______________________, and controls
traits
- Alleles: alternate forms of a ___________________
- Locus: __________________ on a chromosome
- dominant: trait that is expressed with only one copy
needed, and assigned an ___________________ letter
- recessive: trait that is masked and two copies are
needed to be expressed, and assigned
_______________ letter
I. Inheritance of genes on autosomal chromosomes
A. One copy of a trait from mom, one copy from dad
1. ________________________: the actual genes that
a person has (letters)
2. Phenotype: physical appearance of a gene
3. ___________________________: both alleles are
the same (can be big letters or little letters)
4. Heterozygous: the alleles are different
a. All heterozygotes are considered dominant.
Examples:
Homozygous dominant:__________ Heterozygous
dominant: _________ Homozygous recessive:
_________
II. Sex-Linked Inheritance
A. Traits that are controlled by the X or Y chromosome.
1. Most are found on the X chromosome since the Y
chromosome is so _________________________.
2. Women carry two copies of the X chromosome, and
can be ____________________ of recessive traits.
3. Men only have one copy of the X chromosome, so
they are more likely to be affected.
III. Genetic counseling
A. Go to a genetic counselor if you and your mate fear
passing on a ____________________ to a child.
1. Cystic fibrosis: most common lethal genetic
disorder among white people.
a. 1in 20 are carriers.
b. Life expectancy has increased to
_____________________
B. Prenatal Testing for Genetic Disorders
1. Until recently, parents could only screen for
disorders through amnio & CVS.
a. They could then choose
_________________________________.
2. Now parents can harvest ova, screen them, or
screen the actual embryo for problems before in vitro
fertilization.
19.3 DNA Technology
Objectives: Explain how gene _____________________ is being used to treat genetic disorders. Discuss
genomics, including how genomics might lead to better treatments for illnesses.
- DNA technology: our ability to work directly with DNA to determine the relatedness of individuals, to assist
forensics in determining whether a person has committed a crime, and to develop new treatments for human
illnesses.
I. Gene Therapy
A. The insertion of _________________________ material into human cells for the treatment of a disorder.
1. Give people healthy genes to make up for the faulty ones.
2. Over 300 approved gene therapy __________________________
a. 1700 patients
B. Vector: a carrier whose job is to transport the DNA directly into the cell
1. Viruses are converted to do what scientists want.
C. How do you do it?
1. Remove or alter ________________________________ DNA
2. Insert the needed DNA/gene into the virus
3. Allow the virus to infect the person
4. Gardasil
5. Used for treating: familial hypercholesterolemia, cystic fibrosis.
II. Genomics
A. The molecular analysis of a genome.
1. _____________________________: all the genetic information in all the chromosomes of an individual
B. Base Sequence Map
1. 3.16 billion base pairs.
2. Everyone is 99.9% the same!
3. Thought that 50% of the DNA does not code for proteins and considered ‘junk’
4. Think there is 30-50,000 genes.
a. Less than ________________________ of the entire genome.
C. The Genetic Map
1. Tells the location of genes along each chromosome.
2. 16 of the 46 have been mapped so far (this book is 6 years old)
a. chromosome 22 was first (that was the shortest)
3. This ‘junk’ DNA might not even be junk. It may be promoter sequences to help bring proteins to the DNA
for synthesis purposes.
4. With more knowledge comes more power…should we play God?