| h
f ?
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On
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II
AX
HI
Ml *
ft
Hi
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rt IV
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if ? ??
64
11
PLATE III
Karyotype of translocation-mongol boy;
note
the abnormal large acrocentric chromosome. Belozv Belozu four other mitoses.
I3-IS groups from 13?15
are
the
TRANSLOCATION MONGOLISM ARISING DE NOVO? BY P. W. SHORT
Medical Student
Mongolism extra
has
now
been shown beyond doubt to arise as a result of the presence from a small chromosome (No. 21) in the nuclei of cells of
genetic material
ected persons.
TRISOMIC MONGOLS
^he regular
or trisomic mongol has 47 chromosomes, the extra one being a third This chromosome appears in the cells as a result of non-disjunction, occurring at meiosis and occasionally during subsequent somatic divisions. Nonfunction occurs at metaphase, when both daughter 21-chromosomes becomes eluded in the same germ cell. The other daughter cell thus has no No. 21-chromo^e, and is presumably non-viable, as no metaphase plate has yet been seen with this
?- 21.
j.^ally .
formality (Fig.
1). Formation of Gametes
lethal
(a) Non-disjunction
(b) Non-disjunction at second meiotic division: formation of two normal gametes, and one gamete with an extra chromosome. chromosome,
first meiotic division: formation of two gametes with an extra chromosome. at
Fig. if
cell via,
i.
n.0n* disjunction occurs during the first mitotic division of the zygote,
will have 45. 47 chromosomes, and the other J^11 have t^le thus from the cell
one
daughter
The latter cell is not chromosomes and containing 47 emt,ry? develop be stinguishable from a mongol produced as a result of an error during meiotic 2a)- However, if non-disjunction occurs at a later mitotic division of a Iis, l?usly normal zygote, in which cell lines with 46 chromosomes are already estabnew daughter cells with 45 and 47 chromosomes will again result; but as the Cejj chromosomes is non-viable, only one new line of cells will be established, arij he 45 resultant embryo will be a mosaic composed of its original set of cells with one
'
?
.
prev-1?n
8
P. W. SHORT
46 chromosomes, together with a new set (arising from the abnormal division) with 2 47 chromosomes (Clarke et al., 1961; Heyashi et al., 1962) (Fig. 2b). It will be matter of chance which body cells have the abnormal chromosomal constitution. If non-disjunction occurs during a mitotic division of one of the cells of an alread) mongol embryo, the daughter cells resulting from this division will have 46 and 4^ chromosomes respectively and the resultant embryo will be a more complicated mosaic with three cell lines, one with 46, one with 47, and one with 48 chromosome5 (Fitzgerald et al., 1961; Gustavson et al., 1961) (Fig. 2c). Non-disjunction
in mitotic division
Non-disjunction at
occurs
this level
(a) Non-disjunction at the first somatic division of the zygote, resulting in the formation of an individual all of whose cells contain 47 chromosomes.
(b)
Non-disjunction
at
a
division subsequent to the first somatic division, resulting in a two-cell-line mosaic.
Non-disjunction
lethal
(c) Non-disjunction in a mongol embryo, at a division subsequent to the first somatic somatic division, resulting in
three-cell-line mosaic individual.
a
/
\
Fig. 2.
/
\
f ?
n |f
^.X
On
*"
II
AX
HI
Ml *
ft
Hi
?A
* ft i
4 A
rt IV
*A
??
if ? ??
64
11
PLATE III
Karyotype of translocation-mongol boy;
note
the abnormal large acrocentric chromosome. Belozv Belozu four other mitoses.
I3-IS groups from 13?15
are
the
TRANSLOCATION MONGOLISM ARISING DE NOVO? BY P. W. SHORT
Medical Student
Mongolism extra
has
now
been shown beyond doubt to arise as a result of the presence from a small chromosome (No. 21) in the nuclei of cells of
genetic material
ected persons.
TRISOMIC MONGOLS
^he regular
or trisomic mongol has 47 chromosomes, the extra one being a third This chromosome appears in the cells as a result of non-disjunction, occurring at meiosis and occasionally during subsequent somatic divisions. Nonfunction occurs at metaphase, when both daughter 21-chromosomes becomes eluded in the same germ cell. The other daughter cell thus has no No. 21-chromo^e, and is presumably non-viable, as no metaphase plate has yet been seen with this
?- 21.
j.^ally .
formality (Fig.
1). Formation of Gametes
lethal
(a) Non-disjunction
(b) Non-disjunction at second meiotic division: formation of two normal gametes, and one gamete with an extra chromosome. chromosome,
first meiotic division: formation of two gametes with an extra chromosome. at
Fig. if
cell via,
i.
n.0n* disjunction occurs during the first mitotic division of the zygote,
will have 45. 47 chromosomes, and the other J^11 have t^le thus from the cell
one
daughter
The latter cell is not chromosomes and containing 47 emt,ry? develop be stinguishable from a mongol produced as a result of an error during meiotic 2a)- However, if non-disjunction occurs at a later mitotic division of a Iis, l?usly normal zygote, in which cell lines with 46 chromosomes are already estabnew daughter cells with 45 and 47 chromosomes will again result; but as the Cejj chromosomes is non-viable, only one new line of cells will be established, arij he 45 resultant embryo will be a mosaic composed of its original set of cells with one
'
?
.
prev-1?n
8
P. W. SHORT
46 chromosomes, together with a new set (arising from the abnormal division) with 2 47 chromosomes (Clarke et al., 1961; Heyashi et al., 1962) (Fig. 2b). It will be matter of chance which body cells have the abnormal chromosomal constitution. If non-disjunction occurs during a mitotic division of one of the cells of an alread) mongol embryo, the daughter cells resulting from this division will have 46 and 4^ chromosomes respectively and the resultant embryo will be a more complicated mosaic with three cell lines, one with 46, one with 47, and one with 48 chromosome5 (Fitzgerald et al., 1961; Gustavson et al., 1961) (Fig. 2c). Non-disjunction
in mitotic division
Non-disjunction at
occurs
this level
(a) Non-disjunction at the first somatic division of the zygote, resulting in the formation of an individual all of whose cells contain 47 chromosomes.
(b)
Non-disjunction
at
a
division subsequent to the first somatic division, resulting in a two-cell-line mosaic.
Non-disjunction
lethal
(c) Non-disjunction in a mongol embryo, at a division subsequent to the first somatic somatic division, resulting in
three-cell-line mosaic individual.
a
/
\
Fig. 2.
/
\
