Principles of Genetics and Breeding

8.1.2 Androgenesis

Androgenesis is a developmental process, facilitating the inheritance of an exclusively paternal genome. It involves two steps:

• elimination or inactivation of the egg’s genome and
• monospermic or dispermic activation of embryonic development by the haploid or diploid gamete;

Haploid monospermic activation requires restoration of diploidy by suppression of the first mitotic cleavage.

• Reliable protocol for inducing androgenesis, requiring the suppression of the first mitotic cleavage, however, is available for less than a dozen species only.
• Due to irradiation damage suffered by eggs,homozygous expression of lethal genes and damage inflicted by thermal shock treatment to suppress the first mitotic cleavage, survival of the androgenotes is very low.
• Androgenesis is induced in fish by fertilizing irradiated eggs (gamma or X ray or U-V ray) with normal spermatozoa.
• U-V (254 nm) irradiation is easy, inexpensive and can be easily set up under laboratory condition.
• Diploid androgenetic individuals can then be produced by various treatments (thermal, pressure or chemical shock) to suppress the first cleavage division yielding a homozygous diploid.
• Theoretically 50% XX and 50% of YY homozygous individuals will be produced.
• The resultant YY males, if viable and fertile, can be crossed with females to produce XY isogenic (genetically uniform) all-male progeny.
• Androgenetic trout was produced using sperm from tetraploid males and found that these males showed better viability than androgenetic diploid.
• Among the aquarists the male fishes are often found more colourful and beautiful thus commanding a greater demand. It would also be advantageous for species in which the male shows better characteristics for culture, like tilapia.
• In androgenesis, polyploidization by inhibition of meioticphase I and II is impossible due to the distruption of the female nucleus.
• Androgenesis results in a rather low rate of development compared to gynogenesis since the egg cytoplasm as well as the egg nucleus is affected by radiation treatment.
• Androgenesis has not been widely investigated in fish as gynogenesis.
• Like gynogenesis,androgenesis can be used to generate clonal lines.
• An advantage of androgenesis is the option of storing and regenerating lines from cryopreserved sperm by androgenesis; eggs have not yet been successfully cryopreserved in fish and this precludes the storage of gynogenetic lines in that way.
• Androgenetic fishes were successfully produced in tilapia, rainbow trout and Siberian sturgeon. Androgenetic tilapia can beuseful for monosex fish culture.