Thesis (MPhil)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Tilapia is presumed to have a well-defined genetic mechanism of sex determination, but not
all sex ratios are compatible with a monofactorial sex determination model. A theory of
autosomal gene influence, as well as temperature sex determination (TSD) has been proposed
in order to explain large variations in sex ratios. This study assessed the variation in progeny
sex ratio in O. mossambicus as a basis for the application of YY male technology in the
production of all-male progeny groups.
Three populations of O. mossambicus were sampled that are representative of the
geographical distribution of the species in Southern Africa. Progeny groups were produced
from randomly selected parents and maintained at constant temperature during the labile
period of sex differentiation. Variation in sex ratios between different families of the same
strain as well as between different strains was calculated. No significant differences were
observed in sex ratio between strains, though a significant intra-group variation was
identified. This study identified both male and female-biased sex ratios. The data in general
conform to a monofactorial sex determination model. Male-biased sex ratio observed in one
strain can possibly be ascribed to temperature sex determination (TSD). This strain of
O. mossambicus originated from an area with different annual temperature patterns and the
possibility of TSD having an adaptive advantage is discussed.
This thesis also presents the results of a program to produce monosex male tilapia
through the application of the YY male technology in O. mossambicus. Viable XY female
and YY male genotypes were produced. XY females sired progenies ranging from 68-94%
male ofspring, while YY males sired a mean progeny of 94% male phenotypes. From these
results it is concluded that YY male technology provide a viable method for the production of
all-male progeny in O. mossambicus. Once available on a commercial scale, the technology
can be made more reliable through the application of the appropriate selection methods. / AFRIKAANSE OPSOMMING: Tilapia spesies is oorwegend onderworpe aan ‘n goed gedefinieerde enkelfaktor model van
genetiese geslagsbepaling, hoewel afwykings van sodanige geslagsbepalingsmodel soms
waargeneem word. Die invloed van outosomale gene, sowel as omgewings temperatuur
word voorgehou as verklaring van die waargenome variasies in geslagsverhoudings. Hierdie
studie behels die evaluasie van variasie in geslagsdifferensiasie van O. mossambicus as basis
vir die implementering van die YY manlike tegnologie vir die produksie van slegs-manlike
nageslag groepe.
Monsters is bekom van drie populasies van O. mossambicus verteenwoordigend van die
geografiese verspreiding van die spesie in Suider Afrika. Nageslag groepe is geproduseer
vanaf ewekansig gekose ouerpare en by ‘n konstante temperatuur gehuisves tydens die
sensitiewe tydperk van geslagsdifferentiasie. Variasie in geslagsverhouding tussen
verskillende families binne dieselfde subpopulasie sowel as binne verskillende populasies is
bepaal. Geen betekenisvolle verskille is waargeneem in die geslagsverhouding tussen die
verskillende populasies nie terwyl betekenisvolle verskille tussen families binne ‘n populasie
waargeneem is. Die data voldoen aan ‘n enkelfaktor genetiese geslagsbepalingsmodel, met
die uitsondering van een populasies waar ‘n moontlike omgewingsverwante
geslagsbepalingseffek waargeneem is.
Die tesis sluit ook in die resultate in van ’n program om YY-tegnologie in
O. mossambicus te vestig ten einde manlike nageslag groepe te produseer. Funksionele
vroulike XY- en manlike YY genotipes is ontwikkel. Die vroulike XY-genotipes het manlike
nageslag groepe opgelewer wat wissel van 68%-94% manlik, terwyl manlike YY-genotipes
nageslag groepe gelewer het wat gemiddeld 94% manlik was. Die resultate bevestig die
lewensvatbaarheid van YY-tegnologie vir die kommersiële produksie van manlike
nageslaggroepe in O. mossambicus.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16482 |
| Date | 12 1900 |
| Creators | Jordaan, M. S. |
| Contributors | Brink, D., Stellenbosch University. Faculty of Agrisciences. Dept. of Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | Stellenbosch University |
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