12.
G E N E T I C
C Y T O L O G Y
409
Another type of hermaphroditism, known as testicular feminization,
is characterized by a normal male karyotype, negative sex chromatin,
and a female phenotype (Jacobs, Baikie, Court Brown, Forrest, Roy,
Stewart and Lennox, 1959a). The gonads are ofthe male type, however.
This type of anomaly is thought to be inherited through an autosomal
gene (Stewart, 1959).
E .
T R I S O M Y
The most well-known example of trisomy in man is mongolism.
Since the report of Lejeune, Gautier and Turpin (1959), a large number
of mongol cases have been analyzed to substantiate their conclusion
(Book et al., 1959; Lehmann and Forssman, 1960; Makino, Tonomura
and Matsunaga, 1960; Levan and Hsu, 1960). The basic chromosomal
number for mongols is 47, with one of the smallest pair, most probably
pair 21, being trisomic.
Theoretically, the types of trisomy for each species should be exactly
the same as its haploid number. In man, whose haploid number is 23,
therefore, there should be twenty-three possible types of trisomies.
Since the sex pair is dimorphic, trisomy of this pair should have four
possible types, viz. X X X , X X Y , X Y Y , and Y Y Y . Thus trisomy in
man is expected to be of twenty-six types. In Datura stromonium, for
example, all possible types of trisomy have been discovered and described. The addition of an extra chromosome to the genotype usually
causes great disturbances in the phenogenetic processes of the plants,
and the disturbances are usually characteristic for each trisomic type.
It is therefore not completely surprising to geneticists to hear that a
syndrome, such as mongolism, in which multiple congenital deformations exist, is the expression of trisomy. Besides the mongolism and the
sex chromosome trisomy, several other types of trisomy have been
recorded. These include a chromosome belonging to group D (Patau,
Smith, Therman, Inhorn and Wagner, 1960), group C (De Carli,
Nuzzo, Chiarelli and Poli, 1960; Smith, Patau, Therman and Inhorn,
1960), group E (Edwards, Harnden, Cameron, Crosse and Wolff, 1960),
and chromosome No. 22 (Hayward and Bower, 1960; Turner and
Jennings, 1961). Probably more trisomies will be found in man, but it
is doubtful that all trisomies can develop into viable embryos.
So far no clear-cut example of autosomal monosomy is known. The
patient studied by Turpin, Lejeune, Lafourcade and Gautier (1959)
had 45 chromosomes, missing one of the smallest autosomes (21 or 22).
However, in the same karyotype one of the chromosomes appeared
to be abnormal. The authors interpreted it as a translocation product
between chromosomes 13 and 22. If true, there is no real loss of a
G E N E T I C
C Y T O L O G Y
409
Another type of hermaphroditism, known as testicular feminization,
is characterized by a normal male karyotype, negative sex chromatin,
and a female phenotype (Jacobs, Baikie, Court Brown, Forrest, Roy,
Stewart and Lennox, 1959a). The gonads are ofthe male type, however.
This type of anomaly is thought to be inherited through an autosomal
gene (Stewart, 1959).
E .
T R I S O M Y
The most well-known example of trisomy in man is mongolism.
Since the report of Lejeune, Gautier and Turpin (1959), a large number
of mongol cases have been analyzed to substantiate their conclusion
(Book et al., 1959; Lehmann and Forssman, 1960; Makino, Tonomura
and Matsunaga, 1960; Levan and Hsu, 1960). The basic chromosomal
number for mongols is 47, with one of the smallest pair, most probably
pair 21, being trisomic.
Theoretically, the types of trisomy for each species should be exactly
the same as its haploid number. In man, whose haploid number is 23,
therefore, there should be twenty-three possible types of trisomies.
Since the sex pair is dimorphic, trisomy of this pair should have four
possible types, viz. X X X , X X Y , X Y Y , and Y Y Y . Thus trisomy in
man is expected to be of twenty-six types. In Datura stromonium, for
example, all possible types of trisomy have been discovered and described. The addition of an extra chromosome to the genotype usually
causes great disturbances in the phenogenetic processes of the plants,
and the disturbances are usually characteristic for each trisomic type.
It is therefore not completely surprising to geneticists to hear that a
syndrome, such as mongolism, in which multiple congenital deformations exist, is the expression of trisomy. Besides the mongolism and the
sex chromosome trisomy, several other types of trisomy have been
recorded. These include a chromosome belonging to group D (Patau,
Smith, Therman, Inhorn and Wagner, 1960), group C (De Carli,
Nuzzo, Chiarelli and Poli, 1960; Smith, Patau, Therman and Inhorn,
1960), group E (Edwards, Harnden, Cameron, Crosse and Wolff, 1960),
and chromosome No. 22 (Hayward and Bower, 1960; Turner and
Jennings, 1961). Probably more trisomies will be found in man, but it
is doubtful that all trisomies can develop into viable embryos.
So far no clear-cut example of autosomal monosomy is known. The
patient studied by Turpin, Lejeune, Lafourcade and Gautier (1959)
had 45 chromosomes, missing one of the smallest autosomes (21 or 22).
However, in the same karyotype one of the chromosomes appeared
to be abnormal. The authors interpreted it as a translocation product
between chromosomes 13 and 22. If true, there is no real loss of a