Biology Reference
In-Depth Information
phenotypic diversity, explosive speciation rate, and unique endemism,
the African cichlids have attracted the attention of researchers (Gunter et
al., 2011). More than 1,000 species of cichlids representing about 10% of
the world's freshwater species, have arisen within the past million years
in Lakes Malawi and Victoria in eastern Africa (Allender et al., 2003). The
mouthbrooding tilapias also share a common and more recent ancestry
of less than 5 million years (My). Hence the differentiation process of sex
chromosome is of interest. Gnaani et al. (2008) identifi ed DNA markers
linked to sex determining genes in six closely related species of tilapias.
In the female heterogametic
Oreochromis karongae
and
Tilapia mariae
, the
sex determining locus is on linkage group LG3 but it is in LG1 in male
heterogametic
O. niloticus
and
T. zilli
(Table 7). Comparison of genetic
and physical maps suggests relatively stronger sex specifi c suppression
of recombination due to accumulation of repetitive elements in the sex
determining region in female heterogametic
O. aureus
than in male
heterogametic
O. mossambicus
; notably the W and Z homologues of LG3 in
O. aureus
remain cytologically indistinguishable, suggesting one or more
inversions in the W chromosome.
Table 7.
Known linkage groups and sex chromosome systems in selected fi sh
Species
Sex chromo-
some system
Linkage group
(LG)
Reference
Gasterosteus aculeatus
XX/XY
19
Ross and Peichel (2008)
Pungitius pungitius
XX/XY
12
Shapiro et al. (2009)
Oreochromis niloticus
XX/XY
1
Gnaani et al. (2008)
Tilapia zilli
XX/XY
1
Gnaani et al. (2008)
O. karongae
ZZ/ZW
3
Gnaani et al. (2008)
T. mariae
ZZ/ZW
3
Gnaani et al. (2008)
O. mossambicus
XX/XY
3
Gnaani et al. (2008)
O. aureus
ZZ/ZW
3
Gnaani et al. (2008)
Takifugu rubripes
XX/XY
19
Kikuchi et al. (2007)
Oryzias latipes
XX/XY
1
Tanaka et al. (2007)
O. curvinotus
XX/XY
1
Tanaka et al. (2007)
O. luzonensis
XX/XY
12
Tanaka et al. (2007)
O. mekongnensis
XX/XY
2
Tanaka et al. (2007)
O. minutillus
XX/XY
8
Tanaka et al. (2007)
O. dancena
XX/XY
10
Tanaka et al. (2007)
O. hubbsi
ZZ/ZW
5
Takehana et al. (2007)
O. javanicus
ZZ/ZW
16
Takehana et al. (2007)
Poecilia reticulata
XX/XY
12
Watanabe et al. (2005)
Xiphophorus maculatus
XX/XY
24
Bohne et al. (2008)
Salmo salar
XX/XY
2
Artieri et al. (2006)
