Genetic ppt

1. Mitotic Recombination
By
Name:- JYOSHNA RANI KHURA
Branch:-M.Sc.Zoology
School:-School of applied science
Regd.no. :-220705180058

2. • Chromatin recombination is a type of DNA repair
mechanism
• Mitotic recombination was first described by Stern
in his classic drosophila Experiment. For stern,
recombination refers to reciprocal cross-over
(RCOs).
• Most spontaneous RCOs are initiated by DNA
double-stranded breaks(DSBs) and this DSBs
repair requires a template and homologous
chromosomes serve that role it providing the
opportunity for an RCO.
INTRODUCTION

3. When does mitotic recombination occure
Analysis of gene conversion tracts associated with
RCOs provides clues about when during interphase
mitotic recombination takes place.
Normal gene conversion between homologous
chromosomes produces a 3∶1 ratio of alleles
Lee et al. argue that a 4∶0 tract most likely results
when a break occurs prior to DNA replication, but
repair takes place after replication.

4. • It is believed that some sites are hotter for DSB
formation.
• Common fragile sites (CFSs), regions of the
genome prone to chromosomal DSBs, are a normal
feature of mammalian chromosomes, and
analogous regions have been identified in yeast.
• The sites of RCOs, and therefore the initial sites of
spontaneous damage,
Are there hotspots for mitotic
recombination?

5. • RECOMBINATIONAL REPAIRED OF DSB is initiated by 5’-3’
resection and the ssDNA is bound by RPA to control its
accessibility to the Rad51 recombinase.
• 3’ single-stranded ends invade a homologous duplex to
prime DNA synthesis by the process of the DSBR model.
• Now the displaced stranded from the donor duplex pairs
with a 3’ single-stranded DNA tail. Which primes the second
round of DNA synthesis.
• After the ligation of the newly synthesized DNA a double
holiday junction is formed.
• The DHJ can be dissolved by branch migration or
endonucleolytic cleavage .
Repair of DOUBLE STRAND BREAK (DSb)

7. References
• Lisby, M & Rothstein, R.(2015). Cell biology of
mitotic recombination. Cold Spring Harb Perspect
Biol.
• Lafave, Mc & Sekelsky ,J.(2009). Mitotic
recombination: Why? When? How? Where?. PLoS
genet.