Mechanisms of Gene Variation

Describe transformation experiment from Fred Griffith

he infected mice with non-pathogenic strain of Spn (they lived), pathogenic strain (died), pathogenic strain but heat killed (lived), and pathogenic strain heat killed combined with non-pathogen (killed); showed that there was some kind of transformation from pathogenic to non-pathogenic strain

What are the different types of mutations?

substitution and frameshift

What are the three different substitution mutations?

missense, nonsense, and silent

What is a silent mutation?

single substitution that codes for same amino acid

What is a nonsense mutation?

single substitution codes for stop codon too early

What is a missense mutation?

single substitution codes for different amino acid

What are the two different types of frameshift mutations?

deletion and insertion

What is deletion mutation?

one AA deleted so whole thing is shifted back by one amino acid

What is an insertion mutation?

one AA inserted so whole thing is shifted forward by one amino acid

What are examples of frameshift mutations?

Huntington’s, Tay-sachs, colon cancer, prostate cancer, breast and ovarian cancer, HIV

What is a transposon?

jumping genes; transposase cuts the DNA segment out of its original site and moves it directly to a new position without an RNA intermediate

What is a retroransponson?

transcribe DNA into an RNA intermediate and then use reverse transcriptase to copy it back into DNA before inserting it into a new location

What are the different mutagens?

radiation (UV, X-rays), chemicals (smoke, nitrate preservatives, benzoyl peroxide), infectious agents (HPV, H. pylori)

What is a mutagen?

something that can cause cancer

What are thymine dimers?

common type of damage caused by UV light; interfere with both replication and transcription of DNA

What is the repair mechanism for thymine dimers?

visible light with DNA photolyase splits the dimer and removes damaged DNA; DNA polymerase fills the gap by synthezising new DNA; DNA ligase seals the gaps

What are intercalating agents?

things that insert and distort/stretch DNA

Where do microplastics come from and where can they go?

comes from synthetic clothing, tires, nonstick pans, city dust, etc and can go in brain, fish meant, and breast milk

What are conditional mutations?

expressed depending on environmental conditions, especially temperature

What is a way to study lethal mutations?

through conditional mutation; temp sensitive mutations occur naturally, continued in offspring

What is the Ames test?

used to determine if something is a mutagen; rat liver extract with salmonella; plate one plain and one with this solution plus possible mutagen; incubate; a high number of colonies on mutagen plate suggests that the mutagen causes mutations

What is the process of vertical gene transfer?

crossing over; DNA from one cell aligns with DNA in recipient cell; DNA from donor with nick aligns with complementary base pairs in the recipients chromosome; RecA protein catalyzes the joining of the two strands; recipient chromosome has new DNA

What are the three types of horizontal gene transfer?

transformation, conjugation, transduction

What is transformation?

DNA or plasmid uptake by DNA by bacteria; will get new characteristics

What is a partial diploid?

cell or organism that has two copies of some specific genes while remaining haploid for the rest of its genome

What is the difference with site specific and homologous recombination?

only at short, precise target recognition sequences (typically 12–50 base pairs) using specialized enzymes vs swaps genetic material between long stretches of identical or very similar DNA sequences anywhere along the strand

What is conjugation?

F plasmid goes through conjugation pilus and boom

What is HFr conjugation?

a bacterial mating process where a donor cell with an F plasmid integrated into its main chromosome transfers chromosomal and plasmid genes into an F⁻ recipient

What is transduction?

use of bacteriophage to transfer genetic material

Describe the lytic cycle of transduction

phage infects, replication, assembly of progeny phage, release of phage by lysis

Describe the lysogenic cycle of transduction

cell is injected with phage genome; phage DNA integrates with bacterial DNA (prophage), integrated prophage replicates when bacterial DNA replicates