Genetic Transfer (L. 23)

Vertical gene transfer

Transfer of genes from an organism to its offspring.

Horizontal gene transfer

Transfer of genes between cells of the same generation.

What happens during horizontal gene transfer?

A donor cell gives DNA to a recipient cell, and some donor DNA is incorporated into the recipient's DNA.

What is a recombinant?

A recipient cell that has incorporated DNA from a donor cell.

What are plasmids?

Self-replicating circular pieces of DNA, usually found in bacteria, that are about 1-5% the size of a bacterial chromosome.

What types of genes can plasmids carry?

Genes that enhance pathogenicity, such as toxin production, and genes for antibiotic resistance.

What are resistance (R) factors?

Plasmids that encode antibiotic resistance; some can be transferred horizontally.

What are mobile genetic elements?

Genetic elements outside chromosomes that can move between chromosomes or cells.

What are transposons?

Segments of DNA that can move from one region of DNA to another; also called jumping genes.

What do insertion sequences (IS) in transposons encode?

Transposase, which cuts and reseals DNA.

How can transposons affect genes?

They may inactivate genes if they insert within them.

What are complex transposons?

Transposons that carry additional genes, such as genes for antibiotic resistance or enterotoxin production.

How can transposons contribute to horizontal gene transfer?

They can move genes from a chromosome to a plasmid, which can replicate and be transferred between cells.

What is transformation?

Transfer of genes from one bacterium to another as naked DNA.

Where can bacteria obtain DNA during transformation?

From DNA released by dead bacteria into their surroundings.

What did Griffith demonstrate?

Non-encapsulated Streptococcus pneumoniae can take up DNA and become encapsulated.

How can transformation increase bacterial virulence?

Bacteria can acquire genes for capsule formation, allowing them to become more virulent.

What is conjugation?

Transfer of plasmids from one bacterium to another through cell-to-cell contact.

How does conjugation occur in Gram-negative bacteria?

Sex pili, encoded by a conjugative plasmid, attach the cells and allow transfer.

How do Gram-positive bacteria hold together during conjugation?

A sticky substance holds the participating cells together.

What is required for bacterial conjugation?

Opposite mating types: a donor with a conjugative plasmid and a recipient lacking that plasmid.

What is transduction?

Transfer of DNA from a donor cell to a recipient cell through a bacteriophage.

What is generalized transduction?

Random bacterial DNA is packaged inside a phage and transferred to a recipient cell.

What is specialized transduction?

Specific bacterial genes are packaged inside a phage and transferred to a recipient cell.