Download Karyotype

Karyotypes
&
Chromosomal Disorders
Journal Notes
Human Karyotype
Karyotypes
• photograph of one’s chromosomes, grouped
in pairs of homologous chromosomes by size
• Humans have 1 pair of sex chromosomes
(XX or XY) and 22 pairs of autosomes
(chromosomes that are not sex
chromosomes).
Chromosome Abnormalities
• All abnormalities result from an error
during meiosis, called “nondisjunction”
non – dis – junction
• The problem arises when during meiosis
there is a failure of homologous
chromosomes to separate.
Non-disjunction of chromosomes
Nondisjunction of chromosomes
• If non-disjunction occurs, one gamete gets both
chromosomes, the other gamete gets nothing.
Analyzing Karyotypes:
1. Are there 46 chromosomes?
2. Are there 2 identical chromosomes in
each pair of autosomes and 2 sex
chromosomes?
3. Are there any rearrangements between
chromosomes or large, obvious deletions?
Karyotypes DO NOT show:
1. Individual DNA strands or genes or the
DNA sequence
2. The number of genes in a chromosome
3. The presence of gene mutations
6 Chromosome Disorders caused
by Nondisjunction
1.
2.
3.
4.
5.
6.
Down syndrome (trisomy 21)
Edwards syndrome (trisomy 18)
Klinefelters syndrome (trisomy XXY)
XYY syndrome (trisomy XYY)
XXX syndrome (trisomy X)
Turners syndrome (monosomy XO)
**Nearly all other nondisjunctions lead to
death of embryo or child before adulthood!
Chromosome Abnormalities
• Down Syndrome – Extra copy of
chromosome 21. Also called “Trisomy 21”
– Have 47 chromosomes.
• One of only a few trisomy disorders in which the
child has high probability of living to adulthood
– Short stature
– Mental retardation
– Reduced life span
– Characteristic features
Down Syndrome
Lauren Potter from “Glee”
Klinefelter Syndrome
• XXY – Male
– trisomy of the sex chromosomes
•
•
•
•
•
47 Chromosomes
Sterile
Low testosterone
Taller than average
Often don’t know they have it unless
tested.
Klinefelter Syndrome XXY
XYY Syndrome
•
•
•
•
Males with extra Y.
47 chromosomes
Taller than average
Normal development – never know they
have it unless tested.
• May have sterility problems
XXX Syndrome
•
•
•
•
Females with extra X
47 chromosomes
Taller than average
Often develop normally – never know they
have it unless tested.
• May have sterility problems
Turner Syndrome
• XO females.
• Missing 2nd sex chromosome.
– This is the only monosomy in which the
embryo survives. If any other chromosomes
are missing then embryo/fetus does not
survive.
•
•
•
•
45 chromosomes
Sterile
Shorter than average
various other characteristic symptoms
Turner Syndrome - XO