bio214e - Biology 214/414 2009 Packet #4 Omit sections 6.8,...

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Biology 214/414 2009 P a c k e t # 4 Omit sections 6.8, 6.9 Suggested problems: Chapter 6: 1, 2, 3, 4, 5, 6, 7, 11, 12, 16, 22 Bacterial genetics I. The genetic information of bacteria (ie, their DNA) comes in several forms. a. the main chromosome i. almost always circular ii. can contain anywhere from ~ 450 to > 7000 genes iii. During rapid growth ( Figure 6-1 ) bacteria can contain 2 copies of the chromosome, but they are identical, not homologous, copies, so, in the genetic sense, the cells are still haploid. b. “plasmids i. also circular ii. variable in size (a few to several hundred genes) iii. A cell can have 11 or more different plasmids, with various plasmids in characteristic copies per cell (from 1 to several hundred). iv. Some are always autonomous, being independent within the cell, although depending on the cell’s enzymes and resources for replication. c. “Episomes ” are plasmids that can exist either autonomously or integrated into the host’s main chromosome. (eg, Figure 6-10 ) i. There can also be several different ones in a single cell. d. Plasmids and episomes are not essential for cell survival, and in fact are sort of intracellular parasites; but they can provide advantages for the cells as well (eg, resistance to drugs or heavy metals, ability to metabolize otherwise unmetabolizable chemicals, ability to transfer genes to other cells) e. “transposons ” = “transposable elements ” are mobile, semiautonomous DNA molecules f. “temperate” bacteriophage genomes integrated in a quasi-stable way into the bacterial host chromosome
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II. Genetic recombination (defined in its most general sense as the rearrangement of alleles into new combinations) is an extremely important part of life, as it is a crucial part of the process which produces the genetic diversity needed for species survival and evolution. a. In eukaryotes this occurs by crossing over during the first meiotic division during gamete formation and by fusion of the egg and sperm during sexual reproduction. b. But bacteria do not have either of these processes! i. Still, genetic recombination is very important to them as well. ii. Bacteria have 3 processes that allow transfer of DNA between cells so that genetic recombination can occur. 1. These are “transformation ”, “transduction ”, and “conjugation ”. 2. can be transfer of a whole plasmid, part or all of the main chromosome, the genome of a bacteriophage (see below) 3. This is what bacteria have instead of the fusing of sperm and egg. iii. After the transfer, but before the actual crossing over step, cells can be partially diploid for the genes that have been transferred in, and in some cases the partial diploid (“merozygote ”) state is fairly stable. (eg, Figure 6-11 ) iv. After the transfer, crossing over can occur new combinations of DNA as occurs in first meiotic prophase in eukaryotes. III.
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bio214e - Biology 214/414 2009 Packet #4 Omit sections 6.8,...

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