Notes: Karyotypes
s
Human Chromosomes- what you know…
• Humans have 46 chromosomes
(diploid-2N)
• 2 of them are sex chromosomes (X
and Y) they determine what sex
you are
– XX = female
– XY = male
• 44 of them are autosomes  they
do not determine the sex of an
individual.
Sex chromosomes
How is a KARYOTYPE Made?
1. Collect sample:
a. Fetus: amniotic fluid collected during an amniocentesis
or a piece of the placenta collected during a chorionic villi
sampling test (CVS).
b. Newborn: white blood cells
2. Separate dividing & non-dividing cells using chemicals
3. Culture the dividing cells to get a lot of cells
4. Add chemical to stop cell division when chromosome
is compacted
5. Lyse the cells
6. Stain the chromosomes (stain sticks to regions with a
lot of “A” and “T” bases
7. Analyze!
How is a KARYOTYPE Analyzed?
• Use computers to match the homologous pairs.
• We will cut out the chromosomes from a
chromosome spread then arrange them to match
the banding patterns of the homologous pairs
– Use banding patterns, size of chromosome, and
position of centromere
• This type of picture is called a
KARYOTYPE
Chromosome Spread
Karyotype
What does a Karyotype
tell you?
– Sex (male or female)
– Irregular numbers of chromosomes
– Any mutations in the chromosomes
• Basically: all the chromosomes in a cell are
displayed and can be examined for
abnormalities
Is this offspring a girl or boy? How do you know?
Are there any abnormalities in this offspring?
Chromosomal Disorders
• Most of the time, the mechanisms that separate
human chromosomes in meiosis work very well,
but things can go wrong
• The most common error: NONDISJUNCTION
– The chromosomes fail to separate in Anaphase I or II
– The result? Abnormal numbers of chromosomes in
gametes.
Nondisjunction
Prefixes:
dis = absence of / opposite of
non = not
Root Word:
Junction = joining together
• disjunction = the act of separating
• nondisjunction = the act of not separating
Figure 14-15
page 352
Metaphase I
“Trisomy” = 3 copies of
a chromosome
Nondisjunction
(after anaphase I)
End of Meiosis—4 gametes produced
Examples of Chromosomal
Disorders
•
•
•
•
Down Syndrome (3 #21 chromosomes)
Klinefelter’s Syndrome (XXY)
Turner’s Syndrome (XO)
Triple X Syndrome (XXX)
Examples of Nondisjunction resulting in
Chromosomal Disorders
• Down's Syndrome: 47 chromosomes with 3
#21 chromosomes.
• Triple-X Syndrome: 47 chromosomes caused
by 3 X chromosomes.
• Klinefelter's Syndrome: 47 chromosomes
caused by 2 X chromosomes and 1 Y
chromosomes.
• Turner's Syndrome: 45 chromosomes with 1
X chromosome (caused by the absence of one
of the X chromosomes or a Y chromosome).
Chromosomal Mutations
• Chromosomal Mutations
– Deletion
– Duplication
– Inversion
– Translocation
Chromosomal Mutation
(change in number)
• If an organism is
born with the
incorrect number
of chromosomes
– Ex: 47 human
chromosomes
instead of 46
• Result of
nondisjunction
Down Syndrome
• 3 copies of chromosome #21
• 1 in 800 babies in the US is born with this
disease
• produces mild to severe mental retardation
• May not live as long
Klinefelter’s Syndrome
• This is a sex chromosomal disorder
associated with males.
• Nondisjunction causes an extra X
chromosome to be passed along
during meiosis (XXY).
• Resulting male cannot reproduce
• Cases have been found in which
individuals were (XXXY) or
(XXXXY)
• Decrease muscle mass and body
hair
Turner’s Syndrome
• This is a sex chromosomal disorder
associated with females.
• Nondisjunction causes offspring to
inherit only one X chromosome
(genotype = XO).
• Resulting female is sterile due to
underdeveloped sex organs.
• 1/2500 females
Review question..
Who determines the sex of a child?
The mother or the father?
THE FATHER!!!!
Why?
Why does the father determine
the sex of the offspring???
• Mom is XX: she can donate either one
X chromosome or the other X
chromosome to the offspring
(mom can only donate an X)
• Dad is XY: he can donate either an X
chromosome or a Y chromosomes.
– If the offspring receives an X from dad, it is
female
– If the offspring receives a Y from dad, it is
male