CORE CONCEPTS (Microbial Genetics – Week 2)
Haploid vs Diploid
Feature Bacteria (Prokaryotes) Eukaryotes (Humans etc.)
Copies of each
1 (haploid) 2 (diploid)
gene
No recessives → gene always Dominant / recessive / co-
Trait expression
expressed dominant possible
Key phrase: Bacteria = haploid → traits always expressed.
Polyploid Bacteria Example
Deinococcus radiodurans
• Has 4–10 copies of its genome.
• Multiple chromosomes + plasmids.
• Benefit: Massive DNA repair ability → radiation resistant.
Plasmids
• Extra circular DNA.
• Provide bonus traits (e.g., antibiotic resistance).
• Can carry chromosomal genes → when transferred:
→ The receiver becomes merodiploid (= 2 copies of some genes).
How Bacteria Gain New Genes
Mechanism DNA Source Key Feature Example
Free DNA from Streptococcus
Transformation Cell must be competent
environment pneumoniae
Another bacterial
Conjugation Pilus + plasmid transfer F-plasmid
cell
Haploid vs Diploid
Feature Bacteria (Prokaryotes) Eukaryotes (Humans etc.)
Copies of each
1 (haploid) 2 (diploid)
gene
No recessives → gene always Dominant / recessive / co-
Trait expression
expressed dominant possible
Key phrase: Bacteria = haploid → traits always expressed.
Polyploid Bacteria Example
Deinococcus radiodurans
• Has 4–10 copies of its genome.
• Multiple chromosomes + plasmids.
• Benefit: Massive DNA repair ability → radiation resistant.
Plasmids
• Extra circular DNA.
• Provide bonus traits (e.g., antibiotic resistance).
• Can carry chromosomal genes → when transferred:
→ The receiver becomes merodiploid (= 2 copies of some genes).
How Bacteria Gain New Genes
Mechanism DNA Source Key Feature Example
Free DNA from Streptococcus
Transformation Cell must be competent
environment pneumoniae
Another bacterial
Conjugation Pilus + plasmid transfer F-plasmid
cell
