DNA recombination

Question 1

recombination

Answer 1

physical exchange of DNA sequences between chromosomes, to be recombinant, the DNA must have exchanged both of its strands with the other chromosome

Question 2

recombination functions

Answer 2

1. repair DNA damage
2. restart replication forks
3. in bacteria, bacteriophage DNA integration/conjugation
4. in euks, chromosome segregation during meiosis, VDJ antibody, gene expression regulation
5. source of new alleles, diversity, and harmful mutations/disease

Question 3

4 types of recombination

Answer 3

1. HR (least drastic changes)
2. NHEJ
3. transposons
4. conservative site-specific recombination

Question 4

HR

Answer 4

recombination between two homologous DNA molecules; forms Holliday junction in the DNA. Allows for reassortment of genes, gene conversion, new alleles, repair of ss & ds breaks, repair of replication forks, and for meiosis in euks

Question 5

reassortment of genes

Answer 5

when you cross a green pea - tall plant with yellow pea-short plant and get new assortment of green-short and yellow-tall

Question 6

gene conversion

Answer 6

occurs during meiosis when homologous recombination between heterozygotic alleles results in a mismatch in base pairing. This mismatch is then recognized and corrected by MMR causing one of the alleles to be converted to the other. = total loss of 1 allele

Question 7

generation of new alleles

Answer 7

occus by HR, mismatch base pair occurs which is repaired by MMR, repair can cause generation of new alleles

Question 8

Spo11

Answer 8

protein that is expressed during prophase of meiosis, makes ds breaks in DNA to initiate recombination. If nonfunctional, decreased rate of HR can cause nondisjunction, causing trisomy e.g. down syndrome; mutations in SpoII are also the most common cause of infertility

Question 9

errors in HR (ectopic/aberrant recombination)

Answer 9

primarily due to tandem repeats of nucleotides i.e. in microsatellite regions, can cause chromosomal abnormalities i.e. with SpoII

Question 10

unequal crossing over

Answer 10

can cause gene duplication or deletion, can occur due to misalignment at meiosis which can be due to the repeats causing the chromosomes to line up wrong

Question 11

retrotransposon

Answer 11

copy & paste mechanism, RNA transposons, use reverse transcriptase and endonuclease

Question 12

DNA transposons

Answer 12

cut & paste mechanism, DNA transposons use transposase

Question 13

poly-A retrotransposons

Answer 13

retrotransposons that use their poly A tail to bind a T on the DNA and reverse transcribe themselves into the DNA; may recruit cellular mRNA to form processed pseudogenes.

code for RNA binding protein ORF1 and an endonuclease/Reverse transcriptase protein

Question 14

pseudogenes

Answer 14

genomic DNA sequences similar to normal genes but non-functional; lack of promoter, lack of introns, missing 5’ ends, have a series of polyA at the 3’ end, errors in the open reading frame because RT has no proof reading mechanism

Question 15

combinatorial diversity

Answer 15

VDJ recombination for antibodies

Question 16

junctional diversity

Answer 16

NHEJ pathway joins the two gene segments during VDJ, which can result in changes in the DNA sequence at the junction of the two fragments