NONDISJUNCTION
=
a meiotic error that results
in a gamete with an abnormal
number of chromosomes (< 23
or >23)
This
can happen in one of two ways:
1.
matched
pair(s) of chromosomes fail to
separate during
_______________________
2.
sister
chromatids are not
pulled apart during
____________________________
If
the abnormal gamete is
subsequently involved in a
fertilization event, the
resulting embryo will inherit
an abnormal number of
chromosomes (more or less than
the normal 46 chromosomes).
This usually results in
deformities so severe that the
embryo dies (accounting for
20% of all
_______________________________).
Click here for more info on the inheritance of too few or too many chromosomes
Embryos
with <46 Chromosomes
When
nondisjunction results in an
embryo that is ______________
one or more chromosomes, the
embryo usually develops
deformities that are so severe
that the embryo dies.
There is only one exception:
inheritance of a single
X chromosome, without an
accompanying X or Y
(individual also has the
normal amount of 44 non-sex
chromosomes)
Turner’s
Syndrome (karyotype
is written as: 45, X or, if
the individual is a mosaic,
as: 45X/46XX) (=
females with
____________________
chromosome)
Click
here for more info
· Usually
results in fetal death; only
about ________________
survival rate.
· This
is the only case in
which a human can survive with
only 45 chromosomes.
· Individuals
that survive to birth may have
heart, kidney or thyroid
problems and may possess a
thick, webbed neck, but many
appear as normal females until
puberty.
· Have
normal intelligence, but some
with mild learning
disabilities.
· ________________________________________
at puberty (absence of
menstruation, no pubic hair,
and little or no breast
development.
Estrogen therapy
resolves these problems.
· Lacking
true ovaries (only streaks of
undeveloped ovarian tissue and
no oocytes), these individuals
are nearly always (99% of
cases) _________________.
· Commonly
of short stature (only 4 ½ -
5 ft. tall), but can grow
taller if hormone therapy is
administered during puberty.
· Can
occur as a
_______________________ after
fertilization, whereby some
cells contain the chromosomal
anomaly but others contain the
normal complement of 46
chromosomes.
Results from nondisjunction
during mitosis, rather than
during meiosis. Percentages of cells
with the different karyotypes
can vary widely among
individuals and does not
necessarily account for
differences in the severity of
developmental abnormalities. Click
here for more info on mosaics
· Frequency
of occurrence: 1/2500 live
female births
Embryos
with >46 Chromosomes
When
nondisjunction results in an
embryo that inherits one or
more __________ chromosomes,
the embryo usually develops
deformities that are so severe
that the embryo dies. Those
that do survive to birth are
usually severely physically
deformed and rarely survive
past infancy.
There are a few exceptions:
Down’s
Syndrome
(also known as
___________________________)
Click
here for more info
= possession of an
_______________________________________
(the individual inherits three
copies of chromosome #21
instead of two) (If male, the
karyotype is written as: 47,
XY, +21. If female: 47, XX,
+21)
o About
95% of Down’s Syndrome cases
are caused by trisomy 21; 3-4%
are caused when all or part of
chromosome 21 has been
translocated to another
chromosome.
Click
here for more info
o Can
also occur as a mosaicism
after fertilization (see
above).
o Common characteristics: mild to severe learning disabilities, bone deformities, stunted growth, abnormal facial features (e.g. flat nose, small mouth), speech and hearing problems, small hands and feet, small ears, decreased muscle tone, and shortened maximum life expectancy (~55 yrs)
o Life expectancy and
quality of life are strongly
correlated with type of
educational training and
physical therapy, as well as
the age at
which training and therapy
begins.
o Frequency
of occurrence: about 1 in 1000
live births overall, but
frequency increases
with maternal (and possibly
paternal) _________. Here
is a link that explains
paternal
The
remaining cases of chromosomal
anomalies involve individuals
that inherit one or more extra
___________
____________________________
[additional X or Y
chromosome(s)].
Physical and mental
disabilities resulting from
one extra sex chromosome are
typically quite ___________
(with the most common problem
being either low fertility or
infertility).
Sex
Chromosome Variations – incidence rates are
1/500-1000 live births
Click
here for more info
Triple-X
Syndrome (47, XXX)
(=
females with an
___________________ chromosome)
o Results
from nondisjunction of sex
chromosomes in either the
father’s or mother’s
gametes (incidence rates are equal among
the sexes)
o Can
also occur as a mosaicism
after fertilization (see
above).
o Majority
of affected individuals are
unaffected (physically and
mentally normal). Although
some have mild learning
disabilities (such as speech
and language delays and
dyslexia), others have no
problems at all and excel as
honor students.
o _____________________
and menstrual irregularities
may occur, but not in most
cases
o Adult
stature is usually taller than
average, with a tendency to be
overweight
o Not
"more feminine" than
normal females
o Frequency
of occurrence: 1/350-1000 live
female births; the most common
sex chromosome disorder in
females
Klinefelter’s
Syndrome (47, XXY)
(=
males with an
___________________
chromosome) Click
here for more info
o Results
from nondisjunction of sex
chromosomes in either the
father’s or mother’s
gametes (incidence rates are equal among
the sexes)
o Can
also occur as a mosaicism
after fertilization (see
above).
o Physical
appearance is normal, at least
until puberty
o Although
some have mild learning
disabilities (first manifested
as speech delay in toddler
years and, later, as
expressive language problems),
others have no problems at
all, excelling in school and living their lives
without ever even suspecting
that they have an additional
chromosome (often diagnosed
only when seeking diagnosis
for infertility problems)
o Sexual
maturity at puberty may appear
normal; however,
________________________
occurs in most cases (due to
low sperm production),
muscular development is less
pronounced and facial, pubic
and body hair may be sparse or
absent (all due to low levels
of testosterone); some breast
development is also common
(~1/3 of cases)
o Usually
tall and thin before and
during puberty, then tall (ave
is 6 ft ½ in) with tendency
to be overweight in adulthood
o Testosterone
therapy increases strength and
muscle size, promotes the
growth of facial and body hair
o Frequency
of occurrence: 1/500-1000 live
male births; the most common
sex chromosome disorder in
males
Double-Y
Syndrome (47, XYY)
(=
males with an
___________________
chromosome)
Click
here for more info
o Results
from nondisjunction during
_________________________ of
___________________________ in
the father’s spermatocyte (a
normal egg is fertilized by an
abnormal YY-bearing sperm). NOT
due to polyspermy as your
book.
o Can
also occur as a mosaicism
after fertilization. (see
above).
o Sexual
maturation at puberty is
normal, although many have
severe persistent acne, and IQ
is often on the low side, but
still within the normal range
o ____________________
_______ ___________________
(and offspring are usually
chromosomally normal).
o Adult
stature is tall and thin
(usually greater than 6 ft
tall)
o Not
"more masculine"
than normal males
o Incidence
of this condition tends to be
higher in prison populations
than in normal populations,
but there is no clear evidence
linking this condition to
higher levels of aggressive
behavior
o Frequency
of occurrence: ~1/1000 live
male births, but may be more
common (since most affected
men show no obvious symptoms
and are therefore not likely
to be tested)
Inheritance
of more than one extra sex
chromosome (e.g.
48, XXXX; 48 XXXY, 48 XXYY, 49
XXXXX; 49 XXXXY, 49 XXXYY)
o Very
rare. The extra sex
chromosomes do not accentuate
the sexual characteristics,
and the individual is usually
infertile. Usually, the
severity of
___________________________________
increases with the number of
extra sex chromosomes present.
o Can
also occur as a mosaicism
after fertilization (see
above).
Inheritance of a complete
extra set of 23 chromosomes
(46+23 = 69 chromosomes;
called triploidy and written
as either 69 XYY, 69 XXY, or
69 XXX)
Can
occur in two ways:
1.
nondisjunction
of an entire set of
chromosomes during Meiosis I
of gametogenesis: the sperm or
egg ends up with ______
instead of 23 chromosomes
2.
_______________________-
two normal sperm
simultaneously fertilize one
normal egg