Transcript 1 - Lone Star College

Chapter 19
Lecture Outline
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19.1 Chromosomal inheritance
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A. Introduction
1.
Males and females have 23 pairs of
chromosomes
a. Chromosomes 1-44 are autosomes
b. Chromosomes 45 and 46 are the sex
chromosome
a. Males have a Y chromosome and an X
chromosome
b. Females have two X chromosomes
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2. Syndromes can result from
a.
b.
Inheriting of an abnormal chromosome
number
Inheriting abnormal chromosomes
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B. Karyotyping
1.
A display of the chromosomes by size,
shape, and banding pattern
2. Will reveal whether an individual has
inherited an abnormal number of
chromosomes or if a chromosome is an
abnormal length or shape
3. Routine blood test for pregnant women
measures the levels of alpha-fetoprotein,
estriol, HCG, and inhibin-A
a. Abnormal levels have been linked to
certain chromosomal and structural
abnormalities
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4. Amniocentesis
a. Amniotic fluid is withdrawn from the uterus of a
pregnant woman
b. Performed after fourteenth week of pregnancy
c. As many as 400 chromosomal and biochemical
problems can be detected
d. Risk of spontaneous abortion increases by about
0.3%
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5. Chorionic villus sampling (CVS)
1.
2.
3.
4.
5.
6.
A catheter is inserted through the vagina
into the uterus
Chorionic cells in the region where the
placenta will develop are obtained
Can be done as early as the fifth week of
pregnancy
Biochemical tests on the amniotic fluid are
not possible because no fluid is collected
Risk of spontaneous abortion increases by
about 0.8%
Quicker karyotyping results
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Chorionic villus sampling
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6. Preparing the karyotype
1. Obtained cells are stimulated to divide
2. Mitosis is stopped at metaphase
3. Cells are prepared on a slide – dried and
stained
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C. Nondisjunction
1. Can occur during Meiosis I or Meiosis II when
chromosomes do not separate correctly
2. Results in trisomy or monosomy
3. Down syndrome
a. Trisomy 21
1) Three copies of chromosome 21
2) In most instances, the egg had two copies
b. Characteristic physical features
c. Mild to moderate developmental delays
d. Chance of a woman having a Down syndrome
child increases with age
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Nondisjunction during oogenesis
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Down Syndrome
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D. Sex chromosome inheritance
1. Gender of the newborn determined by the
father
a. If a Y-bearing sperm fertilizes the ovum
then the child will be male (XY)
b. If an X-bearing sperm fertilizes the
ovum the child will be female (XX)
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2. Abnormal sex chromosome number
a.
b.
c.
d.
e.
f.
Turner syndrome – female with only one sex
chromosome (XO)
Klinefelter syndrome – two or more X
chromosomes in addition to a Y chromosome
(XXY); sterile male
Poly-X female – more than two X chromosomes
(XXX, XXXX)
Jacobs syndrome – male with one X chromosome
and two Y chromosomes (XYY)
XXY – male
YO – does not live; one X is needed for survival
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Turner syndrome
Klinefelter syndrome
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19.2 Genetic inheritance
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A. Introduction
1.
Genes control:
a. Body traits
b. Production of specific proteins
2. Alleles – alternate forms of a gene having
the same locus on a pair of homologous
chromosomes
a. Dominant allele
b. Recessive allele
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B. Inheritance of genes on autosomal
chromosomes
1.
An individual normally has two alleles for
an autosomal trait
a. Homozygous – identical alleles
b. Heterozygous – non-identical alleles
2. Genotype – genes of the individual
3. Phenotype – physical appearance of the
individual
a. Need only one dominant allele to show
the dominant phenotype
b. Need two recessive alleles to show the
recessive phenotype
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Genetic inheritance
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C. Sex-linked Inheritance
1.
Some sex-linked traits have nothing to do with
the gender of an individual
a. X-linked – control most sex-linked traits – only
on the X chromosome
b. Y-linked - only on the Y chromosome
2.
Sex chromosomes in males (X and Y) are not
truly homologous
3.
Males need receive only one recessive allele to
have an X-linked disorder
4.
Females are usually carriers of the recessive
gene and do not have the disorder; unless they
receive a recessive gene from each parent
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Sex-linked inheritance
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D.
Punnett square
1. Used to determine the probability
of inheriting a particular trait
2. Use uppercase and lowercase
letters to represent the alleles
3. Place father alleles on the top and
mother alleles on the left
4. The possible offspring alleles are in
the inner blocks
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Punnett Square
A
a
A
AA
Aa
a
Aa
aa
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E. Genetic counseling
1.
2.
3.
4.
Helps families understand chromosomal
and genetic inheritance
Helps make informed decisions about
pregnancy and child bearing
If the genotypes of the parents are
known, the counselor can predict the
chances that any offspring will have a
recessive autosomal disorder
If the genotypes are not known, a
pedigree may be utilized
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Inheritance pattern & pedigree for CF
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F. Prenatal testing for genetic disorders
1.
2.
In the past, amniocentesis or chorionic
villi sampling were the best methods to
test for a genetic disorder
Now, ova can be retrieved from the
ovary to test for abnormal alleles
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19.3 DNA technology
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A. Includes working with DNA to:
1.
2.
3.
Determine the relatedness of individuals
Assist in forensics
Develop new treatments for human
illnesses
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B. Gene therapy
1.
Insertion of genetic material into human
cells for the treatment of a disorder
2. Includes:
a. Procedures that give a patient healthy
genes to make up for faulty genes
b. The use of genes to treat various other
human illnesses
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3. Vectors transport DNA into the cell
a.
b.
Modified viruses
Four classes of viruses that have been
used:
1) Retroviruses
2) Adenoviruses
3) Herpes viruses
4) Adeno-associated viruses
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Gene therapy, cont
4.
Other mechanisms used to transport DNA
into the cell:
a. Introduce DNA directly into cells
b. Attaching the genes to a liposome
c. Attaching DNA to molecules which have
specific receptors on the cell
membranes
5. Genes are being used to treat medical
conditions other than genetic disorders
6. Gene therapy is being used as a part of
cancer treatment
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C. Genomics
1.
Molecular analysis of a genome – all the genetic
information in all the chromosomes of an
individual
2.
Two ways researchers have attempted to map
the human chromosomes:
a. The base sequence map
1) Human genetic material contains 3.16 billion
base pairs
2) The order of 99.9% of those base pairs is
identical in all people
3) The total number of truly functional genes is
estimated to be between 30,000-50,000
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Genomics, cont
b.
3.
The genetic map
1) Tells the location of genes along each
chromosome
2) Sixteen of the 46 human
chromosomes have been mapped
Still many unanswered questions including
ethical considerations dealing with gene
therapy and using the information from
genomics
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