Recombinatins .pptx

genetic recombination
types of genetic recombination,how recombination occur, intergenic & intragenci recombination.

1. Recombination ANAND P P 2 ND SEM MSc

2. Genetic Recombination Genetic recombination is the reassortment of genes or nucleotide sequences to produce non parental gene combinations or new linkage relationship of genes. It plays a central role in the evolution of gene diversification. Genetic recombination requires the intimate association of the whole or a part of the genetic material of two or more different genotypes.

3. Why do chromosomes undergo recombination? S pecialized DNA repair systems, S pecialized activities in DNA replication, R egulation of expression of certain genes, F acilitation of proper chromosome segregation during eukaryotic cell division, Maintenance of genetic diversity, I mplementation of programmed genetic rearrangements during embryonic development.

4. Mitotic and meiotic recombination Recombination can occur both during mitosis and meiosis Only meiotic recombination serves the important role of reassorting genes Mitotic recombination may be important for repair of mutations in one of a pair of sister chromatids

5. Genetic Recombination Interchromosomal recombination Intrachromosomal recombination Intergenic Intragenic

6. Genetic recombination 1.Intrachromosomal recombination 2.Interchromosomal recombination Intrachromosomal : take place within one DNA molecule to produce deletions,duplications,inversions & transpositions. Interchromosomal : occurs between two parental DNA molcules,linkage groups or chromosomes to produce a recombinant DNA or recombinant chromosome. # is restricted to Eukaryotes ---- mitotic & meiotic c ross over

7. Intrachromosomal intergenic recombination # Occurs at different loci on the same DNA or chromosome. # It common among Viruses, Prokaryotes & Eukaryotes. # It occurs by mitotic & meiotic crossing over , both these mechanisms are reciprocal. 1.Intergenic 2.Intragenic Intrachromosomal recombination

8. Intrachromosomal intragenic recombination # It occurs between the mutational sites of genes & its rare phenomenon. # It may take place at many sites called Recons . # It may be reciprocal and non-reciprocal

9. Based on the genetic mechanism Homologous / generalized recombination having perfect sequence similarities Non-homologous recombination Site-specific recombination Transposition

10. Homologous recombination

11. Homologous recombination : is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in  non-homologous end joining (NHEJ ).

12. Recombination between homologous DNA sites Homologous recombination allows for the exchange of blocks of genes between homologous chromosomes and thereby is a mechanism for generating genetic diversity Recombination occurs randomly between two homologous sequences and the frequency of recombination between two sites is proportional to the distance between the sites

13. Non homologous recombination

14. Non homologous recombination: When the fragments of DNA are exchanged between two non homologous chromosomes ( dissimilar molecules ) . T ranslocations between different chromosomes or deletions that remove several genes along a chromosome. However, when the DNA sequence at the breakpoints for these events is analyzed, short regions of sequence similarity are found in some cases. For instance, recombination between two similar genes that are several million bp apart can lead to deletion of the intervening genes in somatic cells.

15. Eg : Translocation mutation # Chronic Myelogenous leukaemia ( CML ) : Translocation of long arm of chromosome 22 usually on chromosome 9. Translocation of chromosome generate Philadelphia chromosome is Chromosome 22 & 9

16. Recombination repair DNA breaks Homologous recombination Resection Rad50, Mre11, Xrs2 complex Strand invasion Rad52 Rad51; BRCA2 DNA synthesis     Ligation, branch migration, Holliday junction resolution DSB Non-homologous end-joining Ku70, Ku80 Ligation DSB DNA-PKcs Rad50, Mre11, Xrs2 complex “Cleaning up” of ends XRCC4/Ligase IV

17. Site specific recombination

18. Specialized recombination called Site-specific recombination, first characterized in prokaryotes SSR is responsible for integration of phage genomes into the bacterial chromosomes. Enzymes that catalyze site specific recombination are generally called Recombinase & more than 100 of them are known. Phage integration or related to these enzymes are also known as the Integrase family Classical model of site specific recombination is illustrated by Phage lambda… in lysogenic cycle-------- Prophage formation

19. SSR can generate three different types of DNA rearrangements: 1.Insertion is the addition of one or more nucleotide base pairs into a DNA sequence 2.Deletion ( also called deficiency ) is a mutation in which a part of a chromosome or a sequence of DNA is missing . 3.Inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end, shortly reversing the orientation of a chromosomal segment.

20. Transposition

21. Some genetic elements move to new chromosomal locations by transposition Transposition is a specific form of genetic recombination that moves certain genetic elements from one DNA site to another within the genome. These mobile genetic elements are called transposable elements or transposons or jumping gene or mobile gene.

22. Types of Transposition Cut and paste Transposition ( Conservative ) Replicative transposition Retrotransposition

23. C ut -and- P aste transposition (conservative) In cut-and-paste transposition , an element is cut out of one site in a chromosome and pasted into a new site . The movement is double stranded piece of DNA.

24. Replicative transposition In replicative transposition , an element is replicated, and one copy is inserted at a new site; one copy also remains at the original site . Single Strand is moved

25. Retrotransposition In retrotransposition , t he element makes an RNA copy of itself which is reversed-transcribed into a DNA copy which is then inserted (cDNA )

26. Types of recombination A+ B+ C+ A- B- C- A+ B+ C+ A- B- C- Homologous or general A B C D E F A B C D E F Site-specific att att l att att l integrase Replicative recombination, transposition A B C A B C transposase l E. coli Non homologous recombination

27. Refferences Lewin’s Genes X1 Jocelyn E Krebs Elliotts Goldstein Stephent T Kilpatrick Cell and molecular biology P K Gupta Cell and molecular biology Gerald Karp Lewin’s essential Cell & molecular biology,Genetics & human genetics K K Bhaskaran

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