Download chapter 12 powerpoint notes

Chromosomes and Human
Genetics
Starr/Taggart’s
Biology:
The Unity and Diversity of Life,
Chapter 12
Notes edited by:
R. LeBlanc, MS
(Revised: 1/2012)
9e
•What happens to cell growth and division if gene(s) malfunction?
Spectral Karyotyping
•Orderly cell growth and division are disrupted.
•What is the Philadelphia Chromosome?
•Chromosome #9; the 1st abnormal chromosome responsible for
cancer.
1
2
3
4
5
•What happen to chromosome #9?
•Reciprocal translocation between #9 & #22 causing leukemia, a
type of cancer.
•How does this effect genes on #9?
6
7
8
13
14
15
19
20
9
10
16
21
22
11
17
12
•The gene at the end of #9 is altered by the added gene from #22
causing an abnormal protein (uncontrolled division of white blood
cells).
18
•What is leukemia? (Acute or chronic)
•Abnormal stem cells (Leukemias) over-produce white blood cells
and push-out RBC’s and platelets.
X Y
•What are the function of stem cells?
•Cells that are unspecialized and others become specialized cells
like RBC’s and platelets.
•What are white blood cells and what are their function?
Platelets?
•Part of the bodies defense system.
•Used to help blood clotting.
Key Concepts:
Each gene has its own position in sequence
on a chromosome
Crossing over allows alleles in sequence to
swap places
Allele recombination contributes to
variations in phenotypes
The structure of chromosomes may change
Changes in chromosome structure can give
rise to genetic abnormalities or disorders
Genes and Their Location
Genes are units of information about
heritable traits
Each gene has its own location--a gene
locus--on a particular chromosome
Alleles are different molecular forms of a
gene
Wild-type is most common form of allele.
Any less common form is mutant allele
•How many human genes are there?
•Of the nearly 24,000 human genes found in
human DNA, more than 4,000 have been
patented by private firms and universities, a
new study finds.
Types of Chromosomes
Autosomes
Same in both sexes
Human somatic cells have 22 pairs of
autosomes
Sex Chromosomes
Chromosomes that determine an
individual’s sex (23rd pair)
Humans have 1 pair of sex chromosomes.
Karyotype Analysis (analyze the physical
appearance of chromosomes)
Obtain a sample of
cells; ex. Red blood
Stimulate mitosis with
chemical & incubate.
Add COLCHICINE to
arrest mitosis at
metaphase.
Draw off medium, add saline
solution, and then a fixative.
Centrifuge machine
Take picture of chromosomes; cut and arrange.
Stain cells
1
2
3
4
13
14
15
16
5
17
6
7
8
9
18
19
20
21
10
22
11
12
XX (or XY)
Human Karyotyping
of somatic cells with
22 pairs of autosomes
and 1 pair of sex
chromosomes.
diploid
germ cells
in female
diploid
germ cells
in male
eggs
Meiosis, gamete
formation in both
female and male:
Sex
Determination
in Humans
sperm
X
x
Y
X
x
X
Fertilization:
XY
X
X
X
XX
XX
Y
XY
XY
sex chromosome
combinations
possible in new
individual
XX
Fig. 12.4, p. 196
Characteristics of the Y
Chromosome
Y Chromosome
 The Y chromosome spans about 50 million
base pairs (1.5 – 2% of total DNA).
 The Y chromosome likely contains
between 70 and 300 genes.
 Involved in male sexual determination
and development.
 9 "disease genes" found on chromosome Y
Characteristics of the X
Chromosome
 The X chromosome spans about 155
million base pairs (about 5 percent of
the total DNA in cells)
 The X chromosome likely contains
between 900 and 1,200 genes.
 304 "disease genes" are found on
chromosome X
Human Embryo and Sex
Organ Development
 XY Embryo
 8 Weeks old
 Gene on Y chromosome
governs development of
testes (SRY: Sex-determining
Region on the Y Chromosome).
umbilical cord (lifeline
between the embryo
and the mother’s tissues)
amnion (a protective, fluidfilled sac surrounding and
cushioning the embryo)
homozygous dominant female
recessive male
X-Linked Genes as Clues to
Inheritance Patterns.
Gametes:
1.
1900’s Thomas Morgan
2.
Link between sex
determination & some
non-sexual traits.
(ex. Hemophilia; more
in males)
3.
White eyed flies
appeared genetic
mutations.
4.
Recessive sex-linked trait
or X-Linked)
x
X
X
X
Y
All F1 offspring have red eyes
Gametes:
x
X
X
X
1/2
1/2
1/4
1/2
1/2
1/4
F2
generation:
1/4
1/4
Y
-Why were there no white eyed flies in the 1st
generation?
-Using a punnett square show the cross of
the 2 parents & ratio of F1 offspring.
-Ratio of F2 offspring?
Comparing X-Linked and
Sex-Influenced Traits
A
B
C
A
B
C
Crossing Over and Recombination
• One pair of homologous chromosomes in a
duplicated state (each has 2 sister chromatids)
a
b
c
a
b
c
A
B
C
a
b
c
• 1 Blue & 1 Purple each with 3 different genes
• During prophase of meiosis 2 non-sister
chromatids exchange segments.
• This represents 1 crossover event.
a
B
C
A
B
C
A
b
c
a
b
c
• This is the outcome of the crossover.
•Genetic recombination between non-sister
chromatids.
Chromosomes that can be
distinguished physically with
a special feature are called
cytological markers.
Wx
c
Wx
c
normal chromosome 9
wx
C
wx
C
An abnormal event caused a piece of a
different chromosome to become
attached.
Creighton &
McClintock’s
Experiment
abnormal chromosome 9 (part of
another chromosome attached to it
C = colored seeds;
c = colorless seeds
crossing over
During meiosis crossing over
sometimes occurs.
Notice that the mutant
chromosome is now associated
with c.
Wx
c
wx
C
Wx
C
Wx
c
wx
c
wx
C
recombinant chromosomes
Wx = 2 forms of
starch; wx = 1 form
of starch.
Fig. 12.8, p. 199
Recombination Patterns and
Chromosome Mapping
 Experimental crosses
with Drosophila (fruit
flies)
Crossing over
disrupts linkage
groups (not rare)
Linkage: tendency of genes located
on the same chromosome to be
transmitted together in heritance.
Proved: Certain alleles tend to remain together during meiosis more often than
others because they are positioned closer together on the same chromosome.
Linkage Mapping
 Drosophila melonogaster Chromosomes
X Chromosome
1 Map Unit = 1%
frequency of a crossover
What is the percent frequency
between complete wings & long
wings?
36.1 – 20 = 16.1% (chance of a
recombination)
Probability that crossing over will disrupt linkage genes
is proportional to the distance that separates the 2 loci.
Probability of a Crossover
A
B
C
D
Suppose genes A and B are twice as far apart as two other genes, C and D.
What would be the probability that genes A and B would cross over as
compared to genes C and D?
The probability that crossover will disrupt their linkage is Proportional to the
distance that separates the 2 loci; So…
AB are TWICE as likely to be disrupted by a crossover vs CD which are
HALF as likely to.
Human Genetic Analysis
Pedigrees
Genetic corrections
Polydactyly
Regarding Human
Genetic Disorders
 Genetic abnormality (a rare uncommon version of a trait,
Polydactyly; not life threatening)
 Genetic disorder (inherited condition that sooner or later
will cause mild to severe medical conditions.
 Genetic disease (When workable genes get altered in away
that disrupts body functions)
 Genetic Examples of Disorders and Abnormalities:
 Autosomal recessive/dominant inheritance
 X-Linked dominant/recessive inheritance
 Changes in chromosome number
 Changes in chromosome structure
Disease: an illness caused by infectious, dietary, or
environmental factors; not by inherited traits.
Genetic Disorder
Some Important Genetic Disorders
Patterns of
Autosomal Inheritance
 Autosomal Recessive Inheritance
 Galactosemia (homozygous recessive)
lacking enzyme to digest lactose
 Tay-Sachs
Jewish descent metabolic disorder
Gene #15 mutated; enzyme hexa
produced (dissolves nerve and brain
cells fatty acids)
Harmful quantities of fatty acid are
deposited in the nerve cells of the
brain.
Die by age 5
EXTRA CREDIT (10 PTS): Review the
the movie Lorenzo’s Oil and do a
report (get form online)
Galactosemia
enzyme 1
LACTOSE
enzyme 2
GALACTOSE
enzyme 3
GALACTOSE-1PHOSOPHATE
+
glucose
GALACTOSE-1PHOSOPHATE
intermediate
in glycolysis
• 1 in 100,000 chance of getting this inheritance.
•Enzyme 3 is not produced, so high levels of galactose start to accumulate.
•Galactose can be detected in urine.
•Damages: eyes, liver, and brain
•Untreated = death
•Treatment: restrict dairy products.
Patterns of Autosomal Inheritance
 Autosomal Dominant
Inheritance
Progeria (rapid aging)
Huntington disorder
Progressive involuntary
movements
Deterioration of the
nervous system
Can cause death
Usually noticeable after age
40 causing parents to pass
this on without their
knowledge
Progeria – Too Young to be Old
Fig. 12.16, p. 206
Patterns of
X - Linked Inheritance
 X-Linked Recessive
Inheritance
 Hemophilia
 1 in 7000 males
 Genes do not code for
clotting agent
 Duchenne Muscular
Dystrophy
 X-Linked Dominant
Inheritance
 Faulty Enamel
Fragile X Syndrome (X-Linked recessive
disorder)
•Causes a mutant gene
•Within this gene a segment of DNA is repeated several
times; What kind of mutation is this:
•known as Expansion mutation
•Can you find the Fragile Site????
Fig. 12.15, p. 205
Chromosome Aberrations
The physical structure of chromosomes can change resulting in a genetic disorder
or abnormality. These can occur spontaneously.
Inversion
Translocation
Philadelphia
Chromosome
Chromosome Aberrations
Deletion
Triggered by:
•Viral attacks
•Irradiation (ionization radiation)
•Chemical assaults or other
environmental factors.
Duplication
Note: happens for chromosomes that code
for polypeptides of hemoglobin and is not
harmful.
Changes in
Chromosome Number
Aneuploidy - One extra or one less
chromosome
Polyploidy - Three or more of each
chromosome
Nondisjunction causes changes in
chromosome number (failure to
separate during meiosis or mitosis)
Changes in the
Number of Autosomes
Down Syndrome - Trisomy 21
•1 in 1100 in North America
•Show mental retardation
•40% have heart defects
Changes in the Number
of Sex Chromosomes
 Turner Syndrome X0
 One X chromosome; 1 out of 2500 to 10,000 newborn girls.
 Non-disjunction in sperm accounts for 75% of cases.
 98% abort early in pregnancy.
 Klinefelter’s Syndrome XXY
 1 out of 500-2000 newborns
 Non-disjunction; 67% in moms and 33% in fathers
 Most infertile
 XYY Condition
 1 out of 1000 males
 Tall; mildly retarded; most phenotypically normal
Changes in
Chromosome Structure
Categories of chromosome aberration
Deletion
Duplication
Inversion
Translocation