CHROMOSOME ANALYSIS
CHRONIC FATIGUE SYNDROME
cells instead of 2, causing physical
abnormalities, defective sexual develop-
ment, and infertility. A boy with 1
or more
extra X chromosomes has
Klinefelter's
syndrome,
which causes defective sexual
development and infertility. The pres-
ence of an extra X chromosome in women
or an extra Y chromosome in men nor-
mally has no physical effect but increases
the risk of mild mental handicap.
Chromosomal abnormalities are diag-
nosed by
chromosome analysis
in early
pregnancy, using
amniocentesis
or
chori-
onic villus sampling.
chromosome analysis
Study of the
chromosom es
in body cells to discover
whether a
chromosomal abnormality
is
present or to establish its nature. Fetal
cells for analysis can be obtained in the
uterus by
amniocentesis
or
chorionic vil-
lus sampling
. If a serious abnormality
such as
Down's syndrome
is identified,
termination of the pregnancy and
gen-
etic counselling
is offered. Chromosome
analysis is also carried out when a baby
is stillborn without an obvious cause,
or is born with abnormal physical char-
acteristics that suggest a chromosomal
defect, such as
Turner's sydrome.
Chromosome analysis in children and
adults uses white blood cells taken from
a blood sample. Analysis of the sex
chromosomes may be carried out to
establish the chromosomal sex of a child
in cases where the genitals have an
ambiguous appearance (see
genitalia,
ambiguous
); to confirm or exclude the
diagnosis of
chromosomal abnormalities
;
or to investigate
infertility
.
chromosomes
Thread-like structures in
the nuclei of cells. Chromosomes carry
inherited information in the form of
genes, which govern all cell activity and
function. Each chromosome contains
up to several thousand genes arranged
in single file along a long double fila-
ment of
DNA.
The sequence of chemical
units, or bases, in the DNA provides the
coded instructions for cellular activities.
All an individual's body cells (with the
exception of egg or sperm cells) carry
precisely the same chromosomal mate-
rial copied by a process of
cell division
from the original material in the fertil-
ized egg. Each human cell normally
contains 46 chromosomes made up of
23 pairs. Half of each pair is of maternal
and half of paternal origin. 22 pairs are
autosomal chromosomes, which are the
same in both sexes; the remaining pair
is made up of 2 sex chromosomes. In
females, the sex chromosomes are a
pair of X chromosomes. In males, 1
is
an X chromosome and the other is a Y
chromosome. One sex chromosome (an
X) originates from the mother's egg and
the other (an X in girls; a Y in boys)
from the father's sperm.
CHROMOSOMES
Chromosome pair
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SET OF HUMAN CHROMOSOMES
ch ron ic A term describing a disorder or
set of symptoms that has persisted for a
long time. A chronic illness implies a
continuing disease process with little
change in symptoms from day to day.
(See also
acute.)
chronic fatigue syndrome
A condition
causing extreme fatigue over a prolonged
period, often over years. It is most com-
mon in women aged between 25 and 45.
The cause of the condition is unclear.
In some cases, it develops after recovery
from a viral infection or after an emo-
tional life event such as bereavement.
In other cases, there is no such preced-
ing illness or event. The main symptom
is persistent tiredness. Other symptoms
of the syndrome vary, but commonly
include impairment of short-term mem-
ory or concentration, sore throat, tender
lymph nodes, muscle and joint pain,
129
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