Reproduction by Conjugation

One of the main methods of reproduction by protazoa is conjugation. Ciliated protazoa, namely Paramecium, are the most common forms of protozoa which carry out conjugation. The overall process involves the switching of gametes between paired ciliates or conjugants. Conjugation begins with the joining of two ciliates by their pellicles at the point of interaction.The macronucleus of both conjugants are then broken down and their micronuclei divide by meiosis to form four genetically different pronuclei. Three of these nuclei are destroyed and the fourth divides mitotically to form two genetically identical nuclei. So now there are two genetically identical nuclei within both conjugants. One of these nuclei remains in the original ciliate and the other moves into the paired ciliate. The two conjugants then seperate and the two genetically different nuclei within both ciliates fuse to form a diploid zygote nucleus. The diploid zygote undergoes three rounds of mitosis to form eight identical nuclei. Three of these are destroyed while one stays as the micronucleus and four develope into the macronucleus. Both ciliates now have a micronucleus and a macronucleus that are geneticallly different to their original. The two ciliates then divide by fission to form a number of progeny with one macronucleus and one micronucleus .