Principles of Genetics and Breeding

8.1.3 Gynogenesis

Gynogenesis is a natural form of reproduction in the teleost, Mollienesia formosa.

• Studies by Russian scientists in the early 1960s indicated that gynogenesis also occur in fish under natural condition.
• According to Thorgaard(1986), gynogenesis is an “all-maternal” type of inheritance, where the genetic material of the sperm cell does not contribute to that of embryo.
• It was first described by Hertwig (1911) in frog embryos after the spermatozoa were irradiated with radium gamma rays, prior to fertilization.
• Hertwig showed that with an increasing radiation dose to sperm,the survival of embryos decreased to a zero point, after which a further increase in dose led to an improvement in survival rate and this phenomenon is known as the ‘Hertwig effect’.
• In the normal case, one set of chromosomes from each sperm and egg combine, generating a diploid fertilized egg. However in this case, a haploid embryo containing only one set of chromosomes is generated.
• A small haploid embryo whose eyes are small and whose organs are formed incompletely develop but dies either before or just after hatching.