2. WHAT IS JACOB
SYNDROME?
Jacob's syndrome is a rare
chromosomal disorder
that affects males. It is
caused by the presence of
an extra Y chromosome.
3. Males normally have
one X and one Y
chromosome.
However, individuals
with Jacob's syndrome
have one X and two Y
chromosome.
4. Males with
Jacob's
syndrome, also
called XYY males.
5. What causes Jacob's syndrome?
Jacob's syndrome occurs when
a male inherits two Y
chromosomes from his father
instead of one. He is an XYY
male. Most males are XY.
The exact cause of the XYY
aberration is unknown.
6. WHAT ARE SYMTOMS
OF JACOB
SYNDROME?
learning problems at
school
delayed emotional
maturity
7. What are the Physical
Characteristics of Jacob's
Syndrome?
Males with Jacob’s
syndrome are tall, thin,
have acne, speech
problems, and reading
problems.
9. In 1956, Drs. Joe Hin Tjio and Albert Lavan
confirmed that there were 23 pairs of
chromosomes in humans. Up until that
time, it had been thought that there were
48 chromosomes. However, using a more
advanced experimental technique, Tjio and
Lavan were able to confirm that there are
typically, in fact, only 46 chromosomes.
Because men commonly have 22 pairs of
autosomes, plus one X and one Y sex-
determining chromosome,
10. men are referred to as 46,XY; and
because women commonly have the
same 22 pairs of automsomes plus two
X chromosomes, they are referred to by
geneticists as 46,XX. The discovery by
Tjio and Lavan is generally considered
to be the beginning of modern
“cytogenetics,” which is the study of
chromosomes and the diseases caused
by either numerical and/or structural
abnormalities in them.
11. Three years following this discovery, in 1959, a
young English researcher named Patricia Jacobs
and her associate described the first chromosmal
abnormality in man, the extra
X chromosome that is found in an estimated
80% of the men with klinefelter syndrome; and
later that year, Dr. Jacobs identified the extra X in
trisomy X (47,XXX). Approximately two years
later, in 1961, Dr. Avery Sandberg and his
associates published a paper in the medical
journal Lancet reporting the first man to be
discovered with an extra Y chromosome in his
cells.
