CHLAMYDOMONAS MATING AND CHLOROPLAST INHERITANCE
Introduction :
In addition to the genes on chromosomal DNA in the nucleus, all eukaryotic cells also have DNA in mitochondria
and chloroplasts that is transmitted to and expressed in offspring. The transmission of these organellar genes
differs somewhat from that of nuclear genes. In humans, for example, all mitochondrial genes are transmitted
maternally; your mitochondrial genes came from your mother. In addition to mitochondria, plants also have
another DNA-containing organelle, the chloroplast.
These cells exist in two different "sexes":
mating type plus (mt+) and mating type minus (mt-).
If mitotically dividing cells are deprived of nitrogen, they are induced to become sexually active gametes. When
compatible mating types (+ and -) are mixed, the cells' flagella entwine and clumps of mating cells form.
Eventually the clumps break up into mating pairs of a single mt+ and a mt- cell. These two gametes fuse, initially
forming a cell with four flagella and two separate nuclei (a “quadriflagellate dikaryon”). After a short time
period, the flagella are resorbed into the cell body, the nuclei fuse, the cell wall surrounding the cell thickens, and
a diploid zygote is formed. This diploid zygote is very stable and can exist in nature for very long periods of
time. When conditions are favorable for mitotic growth (i.e., there is enough nitrogen), the diploid zygote
undergoes meiosis to yield four vegetative haploid cells.
The endosymbiont hypothesis proposes that chloroplasts evolved from a once free-living photosynthetic
prokaryotic organism. The genes that have been retained in plant and algal chloroplasts encode a large number
of structural proteins and enzymes of the organelle, together with a number of RNA molecules, including
ribosomal RNAs (rRNAs) and transfer RNAs (tRNAs). Because of the evolutionary origin of chloroplasts, their
Introduction :
In addition to the genes on chromosomal DNA in the nucleus, all eukaryotic cells also have DNA in mitochondria
and chloroplasts that is transmitted to and expressed in offspring. The transmission of these organellar genes
differs somewhat from that of nuclear genes. In humans, for example, all mitochondrial genes are transmitted
maternally; your mitochondrial genes came from your mother. In addition to mitochondria, plants also have
another DNA-containing organelle, the chloroplast.
These cells exist in two different "sexes":
mating type plus (mt+) and mating type minus (mt-).
If mitotically dividing cells are deprived of nitrogen, they are induced to become sexually active gametes. When
compatible mating types (+ and -) are mixed, the cells' flagella entwine and clumps of mating cells form.
Eventually the clumps break up into mating pairs of a single mt+ and a mt- cell. These two gametes fuse, initially
forming a cell with four flagella and two separate nuclei (a “quadriflagellate dikaryon”). After a short time
period, the flagella are resorbed into the cell body, the nuclei fuse, the cell wall surrounding the cell thickens, and
a diploid zygote is formed. This diploid zygote is very stable and can exist in nature for very long periods of
time. When conditions are favorable for mitotic growth (i.e., there is enough nitrogen), the diploid zygote
undergoes meiosis to yield four vegetative haploid cells.
The endosymbiont hypothesis proposes that chloroplasts evolved from a once free-living photosynthetic
prokaryotic organism. The genes that have been retained in plant and algal chloroplasts encode a large number
of structural proteins and enzymes of the organelle, together with a number of RNA molecules, including
ribosomal RNAs (rRNAs) and transfer RNAs (tRNAs). Because of the evolutionary origin of chloroplasts, their
