3.1.3 Transmission of mutations by vertical gene transfer

Vertical gene transfer is the transfer of genetic information, including any genetic mutations, from a parent to its offspring. Bacteria reproduce by binary fission, where the cell grows to twice its original size and then divides into two identical daughter cells. As in humans, the genetic information in bacteria is encoded in DNA, which is packed into chromosomes. During binary fission, the chromosomal DNA is copied, so that each new daughter cell inherits an exact copy of the parent cell’s chromosomes (Figure 21).

Figure 21 The stages of binary fission.

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This figure is a schematic diagram showing the process of binary fission. The bacteria cell is represented as a blue oval surrounded by a blue plasma membrane and a brown cell wall. The chromosomal DNA is represented as a purple squiggle inside the bacterial cell. The process begins with duplication of the chromosomes, represented by an increase in the amount of purple. This DNA is then separated, represented by the presence of two purple squiggles. During this process the cell grows, represented by elongation of the oval. The cell divides giving two cells that are identical to the first image.

Figure 21 The stages of binary fission.

Vertical gene transfer is only one of the ways in which bacteria can spread antibiotic resistance genes. In the next section you will look at another – horizontal transfer.