Binary Fission, Budding and Conjugation

0:00How do microbes multiply and share genes? Let's compare binary fission, budding and conjugation.

0:08Fission and budding are asexual reproduction: one parent makes offspring with the same genes.

0:15Binary fission means splitting in two. A bacterium's main DNA is usually one loop: a circular chromosome.

0:24First, the bacterium copies its DNA, making two identical loops.

0:30Next, the cell grows, the loops move apart, and the middle pinches in.

0:36Then it splits into two daughter cells, each with a full copy of the DNA.

0:42In ideal conditions, some bacteria split every 20 minutes: one becomes two, then four, then eight.

0:50After seven hours, 21 doublings, there could be over 2 million.

0:56Yeast, a single-celled fungus, often reproduces by budding.

1:01A bulge called a bud grows out, and the nucleus divides so the bud gets a copy.

1:07The bud then breaks off as a new cell with the same genes.

1:12Hydra, a small freshwater animal, buds too.

1:16Conjugation is different. Many bacteria carry a plasmid, a small extra loop of DNA.

1:24First, two bacteria join by a thin tube called a pilus.

1:29Then a copy of the plasmid passes across, so both cells now carry it.

1:35The cells separate. One has new genes, but there are still only two cells.

1:41So conjugation shares genes but makes no new cells: it is not reproduction.

1:48Fission and budding make new cells; conjugation only shares genes.