Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 90

Figure 2.18 Conjugation in Paramecium .
Source : From http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=OLIH020P&
File_type=GIF .
cell division, growth, and metabolism, and one micronucleus, which is activated only
during conjugation.
Sexual Reproduction in Paramecium—Conjugation
Sexual reproduction in Paramecium occurs only when environmental conditions
deteriorate. Sexual reproduction involves the exchange of genetic material via cyto-
plasmic bridges during conjugation ( Figure 2.18 ). It is a relatively complex process:
two paramecia join laterally to form a cytoplasmic bridge. The micronuclei of both
conjugants divide by meiosis (producing haploid micronuclei). Each conjugant then
donates a micronucleus to its partner. After exchanging genetic material, conjugants
separate and both organisms produce a new macronucleus to replace the original
macronuclei that disintegrate during the process. Thus, half of the new nuclear appa-
ratus derives from the conjugant. The paramecia now are ready for asexual reproduc-
tion through binary fission.
Reproduction in Fungi
Fungi are a separate kingdom of eukaryote organisms with a nucleus, chromosomes,
and organelles. Yeasts, molds, and mushrooms belong to this group. Like animals,
they are heterotrophic organisms that use plant- or animal-derived materials as
sources of food, and their cell walls consist of chitin. Similar to plants, they have cell
walls and vacuoles and produce spores.