Recombination Final.ppt
- 1. PRESENTED BY PRASHANT VC DEPT OF ZOOLOGY GUK Recombination
- 2. Definition of recombination Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
- 3. Types of recombination A- B- C- B+ C+ A- A+ B+ C+ A+ B- C- Homologous or general Nonhomologous or illigitimate A B C D E F A B C D E F Replicative recombination, transposition A B C A B C transposase Transposable element att E. coli Site-specific att l att att l integrase l
- 4. Definition of recombination Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
- 5. Definition of recombination Breaking and rejoining of two parental DNA molecules to produce new DNA molecules Reciprocal recombination: New DNA molecules carry genetic information from both parental molecules. Gene conversion: One way transfer of information, resulting in an allele on one parental chromosome being changed to the allele from the other homologous chromosome
- 6. Gene Conversion Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event. Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another. A+ B+ C+ A- B- C- A+ B+ C- A- B+ C+
- 8. Gene Conversion – Characteristics Gene conversion involves the unidirectional transfer of genetic material from a ‘donor’ sequence to a highly homologous ‘acceptor’ and occurs in both meiosis and mitosis. Gene conversion is initiated by DNA double‐strand breaks and appears to arise from different mutually exclusive pathways. The rate of gene conversion is mainly determined by sequence homology and by the distance between the interacting sequences. Interallelic gene conversion events occur between alleles on homologous chromosomes whereas nonallelic or interlocus events can occur between paralogues on the same chromatid, sister chromatids or homologous chromosomes.
- 9. Gene Conversion – Characteristics Interlocus gene conversion events have driven the concerted evolution of many human gene families whereas interallelic events have generated a high level of allelic diversity at certain loci. Gene conversion has also been implicated as the cause of a variety of different human inherited diseases. In stark contrast to the frequent detection of pathogenic interlocus gene conversion events, the occurrence of interallelic gene conversion events causing human inherited disease is quite rare. Only a few well‐documented examples of gene conversion events in cancer have been reported in the literature. Gene conversion can account for the occurrence of some recurrent mutations on different chromosomal backgrounds in different ethnic groups. Gene conversion may provide a possible future means to bring about ‘natural gene therapy’ by offering an important alternative to the introduction of an entire functional gene.
- 10. Holliday model
- 13. Resolution of joint molecules Can occur in one of two ways The Holliday junction can be nicked in the same strands that were initially nicked = “horizontal resolution.” This results in NO recombination of flanking markers. The Holliday junction can be nicked in the strands that were not initially nicked = “vertical resolution.” This results in RECOMBINATION of flanking markers.
- 14. Holliday Junction Model THANK YOU