Download IV. Diagnosing Gene Disorders

Genetic Disorders Notes
Integrated Science 2
Name:
Per.
I. Overview of DNA Structure
A. Review
1. A
is a segment of DNA that codes for a particular
.
2. Proteins determine the
of an organism.
3. In humans, DNA is organized into 23 pairs of
chromosomes.
B. DNA Structure
1. The basic building block of DNA is a
.
2. Nucleotide chains are held together to form a
.
3. Nucleotides are represented using the letters
.
II. DNA Based Disorders.
A. Dysfunctional Genes
1. A gene can be
some of its nucleotides or some of the nucleotides present may be in
the
.
 The protein made from that gene may
.
B. Missing Genes
1. A person can be born missing
or
of a gene.
 No protein is produced and the trait
.
C. Examples of DNA Based Disorders
1. Sickle-cell anemia
 Caused by a substitution of one nucleotide in the allele for normal
.
 Red blood cells become
in stressed conditions and die in 10 to 20
days (normal blood cells live for _________ days) leading to ____________.
 These tend to become stuck in capillaries, leading to
.
 Most common among individuals with
, because it provides
a resistance to
,
2. Huntington’s Disease
 Produced by a single
.
 A gradual change of the
occurs around the age of
.
 Marked by a painful, progressing loss of muscle control and mental function until death occurs.
 Approximately __________ in 100,000 affected
III. Chromosomal Based Disorders
A. Causes
1. Nondisjunction
 During meiosis I, homologous chromosomes do not
.
 Results in an extra copy of chromosome in one cell, and a loss of that chromosome from another.
B. Results
 After fertilization, the resulting person will have an
.
 A
cell has one missing chromosome.
 A
cell has one extra chromosome.
C. Nondisjunction of Sex Chromosomes
 Genes critical to all embryonic development are on the
.
o Absence of the X chromosome is
, absence of the Y chromosome is
lethal.
 Individuals can survive if they have an extra
chromosome.
 Affects approximately 1 birth in every _____________.
Disorders involving Sex Chromosomes
1. Klinefelter Syndrome males with extra
. Can be XXY or XXXY.
 affects 1/500 births.
 Abnormal development of the testis, leading to ____________________.
 Affected individuals are often ________ and produce relatively small amounts of _______________
2. Triple X syndrome females with extra
(XXX or XXXX).
 Affects 1/1000 female births.
 Affected individuals are usually ____________ than average and have ______________ builds.
 Normal development of sexual traits and are _____________.
3. Turner Syndrome females with only one
 affects 1/2000 live female births.
 Only 1 in ___________ affected zygotes develops to term.
 Individuals are short in stature, generally lack prominent female secondary sexual characteristics, and
may be __________________.
 Health problems such as __________________, kidney problems, diabetes and thyroid problems.
D. Nondisjunction of Autosomal (non-sex) Chromosomes
 Can affect chromosomes
.
 Only 3
result in a baby that can survive for a time after birth.
 Most frequently, the baby dies in utero.
1. Down Syndrome –
 one extra
. (written as 47, +21).
 1/800 live births
 Life expectancy ___________________ but heart problems persist
 lower than average mentally.
 Decreased muscle tone, flat _________, eyes slanting up, irregular shaped ears, large tongue relative
to the mouth.
IV. Diagnosing Gene Disorders
A. Karyotype-a display of all the
.
1. The process:
 Harvested cells in metaphase are
.
 Chromosomes are observed under the microscope.
 A photograph is taken and enlarged.
 Chromosomes are arranged in
.
 Abnormalities are identified.
B. Prenatal Diagnosis
1. Carrier Identification Tests
 CVS (chorionic villus sampling) – a needle is inserted into the mother’s _______________ to test for
DNA, gene, and chromosome disorders.
 Ultrasound – detects major ___________________ deformations
 Amniocentesis – fluid is removed from the sac around the embryo to detect _____________________
abnormalities
 Fetal blood sampling – needle is used to remove cells from the fetus to test for ____________ disorders.
V. Preventing Genetic Disorders
A. Blood Test
 Simple blood test in males and females can screen for more than __________ genetic mutations
 Approximately ________ and the results are available in less than a week.
B. In Vitro Fertilization
 Doctors screen embryos after fertilization and only implant those that appear free of ________________