DNA Recombination- Lecture 31 Flashcards
What are the defining features of generalized recombination?
homology based
catalyzed by REC proteins
What are the defining features of transposition recombination?
not homology based
catalyzed by transposase (Tnase)
Why are children of the same parents not identical?
because there is random assortment of chromosomes and recombination occurs between the pairs of chromosomes prior to formation of gametes
Explain the events and outcome of equal crossing over.
homologous recombination between similar sequences on two chromosomes that line up perfectly
results in some diversity in the sequences of the two chromosomes
normally no major consequences
Explain the events and outcome of unequal crossing over.
homologous copies of the gene align out of register and undergo recombination, resulting in unequal distribution of gene copies
results in two or more copies of the same gene present on a chromosome
may cause disease
Explain the events and outcome of intrachromosomal recombination at inverted repeats on the same chromosome.
regions of homologous sequences at repeats can “flip” over onto each other, creating a hairpin loop-like structure and recombination occurs
results in sections of genes being inverted (in the improper order)
What is a pathogenic example of inverted repeats on the same chromosome?
hemophelia- Factor 8 does not get expressed in males with this because the X chromosome copy has inverted sequences that cannot form functioning proteins
A _____ could allow substitution of a gene mutation on a chromosome with an exogenous wild type copy that has been introduced into the cell by lentivirus vector.
double crossover event
____ is the movement of a unit of DNA called a “transposon” from one sit to a new target site.
Transposition
What is the one mentioned mechanism for movement of bacterial transposons?
cut and paste (non-replicative) mechanism
Describe the cut and paste mechanism for movement of bacterial transposons.
ends of the transposon unit in the donor DNA are recognized by transposase, which makes cuts at those ends as well as staggered cuts in target DNA site; transposon DNA is inserted in the target site (can be same of different DNA molecule as donor)
What are the two types of transposons in prokaryotes?
IS elements (insertion sequence)- carry only transposase code Complex Transposons - carry a gene for antibiotic resistance in addition to transposase
Provide examples for bacterial transposons carrying antibiotic resistance.
ampicillin resistance gene (Tn3)
tetracycline resistance gene (Tn10)
What is the eukaryotic version of movement of transposons?
eukaryotic retrotransposons (move via an RNA intermediate)
Describe the pathway of eukaryotic retrotransposons.
transposon DNA sequence is transcribed by RNA polymerase, creating an RNA copy of the transposon sequence; reverse transcriptase conversion of RNA intermediate to double stranded DNA –> integrates into target DNA via integrase protein
