Mistakes in Meiosis
Problems with DNA
Human Chromosomes


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46 chromosomes in 23 pairs.
22 pairs of autosomes (44)
2 sex chromosomes
XX = female
XY = male
Y has few active genes &
carries genes for maleness.
Nondisjunction



Failure of
homologous
chromosomes to
separate during
meiosis.
Can result in
severe
abnormalities.
Diagram(right) Anaphase I
Results of
Nondisjunction


Monosomy - possess one less
copy of an chromosome.
Trisomy - possess one extra
copy of a chromosome.
Disorders caused by
Nondisjunction

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
Downs Syndrome (trisomy)
Turners Syndrome (monosomy)
Klinefelters Syndrome (trisomy)
Downs Syndrome



Extra
chromosome 21.
Affects physical
& mental
development.
More likely to
occur in
pregnancy of
older women.
Klinefelters Syndrome


Xy plus an
extra X results
in XXY
individual.
Sterile male
with female
characteristics.
Turners Syndrome


Missing an X
results in XO
individual.
Sterile female
with
characteristic
appearance.
Nondisjunction - Sex
Chromosomes

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
XX plus a normal X results in
XXX individual.
Sterile, but otherwise normal
female.
YY plus normal X results in XYY
individual. Fertile males with
normal appearance - Greater
numbers of individuals in penal
institutions.
Other Chromosomal
Mutations




Translocation
Duplication
Deletion
Inversion
Translocation

Transfer of one
section of a
chromosome to
a non homologous
chromosome.
Deletion

A portion of a
chromosome is
taken away from
a chromosome.
Duplication

A portion of the
is duplicated so
that there are
multiple copies
of that sequence
on the
chromosome.
Inversion

A portion of a
chromosome
breaks off &
then becomes
reattached to
the same
chromosome in
an inverted
fashion.
Techniques for Detecting
Genetic Disorders


Genetic Screening - analysis of
blood or urine for presence of
enzymes or chemicals.
Karyotyping - photograph of
paired homologous
chromosomes.
More Techniques


Amniocentesis Removal of
amniotic fluid
for chemical
analysis.
Chorion villi
sampling
Mutagenic Agents


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Radiation - X-rays, UV
rays, radioactive
substances & cosmic
rays.
Chemicals formaldehyde,
benzene, asbestos,
nicotine
Non-disjunction
increases as mother’s
age increases.