Sex in Protists
By Linda Hufnagel, University of Rhode Island
Protistan sexual activities are as diverse as the protists themselves. Providing
an opportunity for genetic recombination, protistan mating interactions may
involve gametes (+ and -, male and female, type a and type a, macrogametes and
microgametes, etc) or mating types (which can vary from two, like humans, to
many! How confusing that must be!!). Sexual reproduction is a misnomer, because
reproduction of the participants does not take place until after the important
events have occurred. The significant events of sexual processes in protists
are meiosis, to produce haploid genomes, and fusion of gametes (as in Chlamydomonas
or Plasmodium) or gametic nuclei (as in the ciliates Tetrahymena and Paramecium),
to bring about new combinations of genetic information. In many protists, a
sexual cycle has not been found, but that could be because the shy creatures
do not wish to be observed in the act! All kidding aside, in these so-called
non-sexual species the conditions required for the cells to become mating competent
may not yet have been identified.
Scientists are researching many interesting aspects of mating in protists, including
the production and properties of mating signals (pheromones) and their receptors,
secretion of mating specific agglutinins and morphogenetic changes in the participating
cells. Particularly exciting and unique is the process of macronuclear development
in mating cilioprotists, during which a new, polygenic macronucleus is formed
from a diploid micronucleus recently formed by fusion of haploid nuclei. The
old macronucleus undergoes apoptosis, but not before it leaves its mark on a
new mac, leading to the non-mendelian inheritance of phenotypic properties.
Here is a small selection of web sites with images and information about mating
a biotech company Ambion discusses gene sequence elimination during MIC to MAC
conversion in the ciliate, Tetrahymena
basic events of conjugation in Tetrahymena.
Images of mating Paramecium
Mating in Tetrahymena
is described, with accompanying fluorescent images.
Methods are described, for DNA-mediated transformation in Tetrahymena
with accompanying diagrams.
Inheritance in ciliates is summarized; from Developmental Biology, by Scott
the web site of Martin Gorovsky, with information on his research on mating
Research on mating in Chlamydomonas, from the laboratory of Ursula Goodenough.
mating research from the laboratory of William Snell.
Information on mating in Chlamydomonas
Agglutination mutant affecting mating in Chlamydomonas
a method for looking at the transmission or organellar genes during mating in
a student report on Chamydomonas
, by Alexander Cuenca, from the University
An introduction to mating in Chlamydomonas
mating in the yeast, Candida albicans
mating types in yeast.
about yeast mating type switching.
a yeast mating movie.
sex in slime molds