Principles of Genetics and Breeding

8.1.1.1 Methods of chromosome manipulation

1. Inactivation of gametes

• This involves irradiating spermatozoa with gamma radiation, X-ray or U-V light or by chemical treatment (like dimethylsulphate) to destroy the genetic material without inactivating the spermatozoa.
• UV irradiation form pyrimidine dimers in DNA leading to its genetic inactivation. For complete inactivation of genomes the optimum dose of UV varies with spermatozoa concentration.
• By using these de-chromosomed spermatozoa to activate the eggs followed by shock treatment (to prevent II Pb release), XX condition is established.
• To induce androgenesis, the maternal (egg) genome is inactivated by irradiation and fertilized with normal sperm.
• Fish eggs are more difficult to manipulate than spermatozoa for their large size.
• Gynogenetic and androgenetic individuals are normally haploids with low survival rate. To improve their survival rate, they have to be diploidized by shock treatment.