s notes: karyotypes human chromosomes- what you know… humans have 46 chromosomes (diploid-2n) 2 of...
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s Notes:
Karyotypes
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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
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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 chemicals3. Culture the dividing cells to get a lot of cells4. Add chemical to stop cell division when chromosome is
compacted5. Lyse the cells6. Stain the chromosomes (stain sticks to regions with a lot of
“A” and “T” bases7. Analyze!
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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
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Chromosome Spread
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Karyotype
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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
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Is this offspring a girl or boy? How do you know?
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Are there any abnormalities in this offspring?
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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.
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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
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Figure 14-15page 352
Nondisjunction(after anaphase I)
Metaphase I
“Trisomy” = 3 copies of a chromosome
End of Meiosis—4 gametes produced
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Examples of Chromosomal Disorders
• Down Syndrome (3 #21 chromosomes)• Klinefelter’s Syndrome (XXY)• Turner’s Syndrome (XO)• Triple X Syndrome (XXX)
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• 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).
Examples of Nondisjunction resulting in Chromosomal
Disorders
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Chromosomal Mutations
• Chromosomal Mutations
– Deletion
– Duplication
– Inversion
– Translocation
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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
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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
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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
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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
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Review question..Who determines the sex of a child?
The mother or the father?
THE FATHER!!!!Why?
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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