Differentiation in Hermaphrodites - Genetic Sex Differentiation in Fish - page 114

Among the gonochores, the role of sex determination by the Dmy/
Dmrt1bY has been unquestionably confi rmed in a couple of medaka fi shes.
The claim of amh in tilapia (Shirak et al., 2006), Dmrt1 in sturgeon (Hale et al.,
2010) and Dmrt1/cyp21a2 in zebrafi sh (Bradley et al., 2011) as candidate genes
for sex determination remains to be confi rmed. So far no sex determination
gene has been identifi ed in any of the hermaphroditic fi sh.
By pedigree based genetic parameter estimates, Batargias (1998) has
established a genetic correlation between body weight and sex change
in the gilthead seabream S. aurata . Through an interesting investigation,
Loukovitis et al. (2011) have brought evidence for the genetic control of
sex change in this non-model seabream. Combining body growth and sex
change to non-monogenic traits, they have demonstrated a fast and effective
strategy for QTL (Quantitative Trait Loci) detection through comparative
genomics and linkage analysis. A BAC sequence information for SNP
detection to enable fi ne mapping of QTL has also been developed. Analysis
of 10 paternal half sib-families comprising of 409 progenies has revealed
the presence of two sex linked loci in saLG21 group, namely one QTL for
body weight and another affecting sex determination.
By estimating sex specifi c growth from a comparative study of growth
rings in otoliths of α females with highest potential for sex change in harems
of different densities of the wrasse H. miniatus, McCormick et al. (2010)
have noted that the α female underwent growth acceleration at sex change.
Hence, it is likely that S. aurata change sex at specifi c body size, whereas
in the haremic H. miniatus the α female undergoes growth acceleration at
sex change.
3.6 Sex differentiation genes
The subfamily Epinephlinae, commonly known as groupers, includes 159
species in 15 genera; the genus Epinephelus alone comprises of 98 species.
Groupers are widely distributed throughout the tropical and subtropical
waters of the world. Being a favorite marine food-fi sh, they are commercially
important. They are amenable for culture, grow fast and resist diseases.
Hence there is a growing interest for aquaculture of groupers. Being
protogynous hermaphrodites, the males are however not readily available.
Chinese scientists seem to have launched a major program to understand
the molecular mechanism of sex change in the groupers. Not surprisingly,
almost all available information on sox genes concerns the orange-spotted
grouper E. coioides (Table 26). Using cDNA plasmid libraries from pituitary,
hypothalamus and gonads at different phases of the orange spotted grouper,
many scientists have constructed a set of SMART (switching mechanism
at 5΄ end of the RNA transcript). To date, Chinese scientists have cloned
and identifi ed the following genes: 1. sox3, which plays a regulatory role