The Molecular Basis of Gene conversion ppt.pptx

Its a presentation of gene conversion overview giving a concept of how this phenomenon works

1. “The Molecular Basis of Gene conversion in Ascobolus sp.” Presented by : Hunaina Tanveer Roll No. : BSBT-38F23 Presented to : Dr. Summera Jahan , Dr. Samia Akram

2. Content : Gene conversion Process Double Holliday Junction. Gene conversion in Ascobolus sp.(Howell and Lamb experiment, Yeadon et.al work.) Factors Effecting the Hybrid DNA Formation in Ascobolus Why the Ascobolus is used to study gene conversion Importance of studying Gene Conversion References. 1

3. Gene conversion : Gene conversion is a non-reciprocal recombination process where a donor sequence corrects or modifies an acceptor sequence without being altered itself. This phenomenon can occur between homologous chromosomes, sister chromatids, or even within the same chromatid. The process is initiated by a double-strand break (DSB) in the DNA, followed by 5'- end resection to form 3' single-stranded DNA tails. These tails then invade the homologous sequence, leading to the transfer of genetic information. 2 www.sciencedirect.com

4. Process: Double-Strand Break : A DSB is generated within a duplicated or repeated sequence, initiating the gene conversion process. 5’-3’ Resection: The DSB undergoes 5'-end resection, forming 3' single- stranded DNA tails capable of invasion. Strand Invasion: The 3' tails invade the homologous sequence, leading to the formation of heteroduplex DNA. Further processing: DNA Synthesis and Resolution DNA Synthesis occurs, followed by resolution of the heteroduplex, completing the gene conversion process Spo11: enzyme which causes the double strand to break for gene conversion. 3 https://images.app.goo.gl/9X2uun3X39gTZcC19

5. Double Holliday Junction Mechanism in Gene Conversion Process: Process : A double-strand DNA break is repaired by strand invasion, where one strand invades a homologous sequence. Results in two interconnected structures known as Holliday junctions. Resolution Outcomes : Crossing-Over Resolution: Cutting outer strands of both junctions. Leads to crossover events, exchanging large chromosomal segments. Non-Crossing-Over Resolution : Cutting inner strands of one junction and outer strands of the other. Results in non-crossover events, transferring small DNA segments without exchanging large regions. The DHJ mechanism is central to meiotic recombination, determining whether gene conversion involves large-scale crossover or localized non-crossover events. 4 https://images.app.goo.gl/NogzW7qDwHMok8Cg8

6. Gene Conversion in Ascobolus immersus : (Methylation Transfer & Genetic Controls ) Experimental Setup: Methylated and unmethylated alleles of the b2 spore color gene were paired during meiosis. Observation: Methylation transferred frequently to the unmethylated allele. Directionality: Transfer was polarized along the gene's 5' to 3' direction, resembling gene conversion patterns. Implications: Methylation acts as an epigenetic mutational mechanism, affecting gene expression during homologous recombination 5 https://images.app.goo.gl/QY8iK8TPpVKYfbgM6

7. 6 Results 0f Howell and Lamb experiment www.sciencedirect.com

8. Genetic Controls of Gene Conversion: Key Factors Identified: ccf-5 (w-9 locus) and ccf-6 (w-BHj locus). Forms: Each exists in two forms (A and B). Function: Regulate gene conversion rates at specific loci. Conclusion: These findings provided foundational insights into how epigenetic modifications and genetic controls influence recombination and inheritance in Ascobolus. 7

9. Yeadon et al. Study: Insights into Gene Conversion at the w-9 Locus in Ascobolus immerses: Key Findings: Hybrid-DNA (h-DNA) Formationccf-5 determines the symmetry of h-DNA formation, controls which chromatid invades during asymmetric h-DNA formation. Mismatch Correctionccf-5 influences the correction of DNA mismatches during gene conversion. Corresponding-Site Interference (CSI)ccf-5 affects CSI, altering the likelihood of h-DNA formation on chromatids. Gene Conversion Frequency Higher in ccf-5 homozygotes (10.7%) vs. heterozygotes (3%). Conclusion: Yeadon et al. expanded our understanding of Ascobolus gene conversion, highlighting the pivotal role of ccf-5 in h-DNA formation, mismatch correction, and conversion efficiency. 8

10. Factors Effecting the Hybrid DNA Formation in Ascobolus : γ 1 is CSI-focused and impacts the interaction between chromatids. γ 2 is h-DNA-focused, influencing the symmetry and chromatid invasion mechanics. ccf-5 has a broader role, linking mismatch correction, h-DNA formation, and gene conversion rates, making it the central regulatory factor. ccf-6: Focuses on gene conversion frequency specifically at the w-BHj locus, ensuring locus-specific control of recombination events. Corresponding-Site Interference (CSI): Positive CSI: Hybrid DNA formation on one chromatid increases likelihood on the other. Negative CSI :Hybrid DNA formation on one chromatid decreases chance on the other. 9

11. Why the Ascobolus is used to study gene conversion: 10

12. Importance of studying Gene Conversion: 11 Uses

13. CONCLUSION : 12 "In conclusion, studying gene conversion in Ascobolus sp. helps us understand how genetic information is transferred and modified during recombination. The process, which starts with double-strand breaks and includes mechanisms like the Double Holliday Junction, plays a key role in maintaining genetic diversity and accuracy. Research by Howell, Lamb, and Yeadon has shown how factors like methylation and specific genetic controls (ccf-5 and ccf-6) influence the process. Ascobolus sp. is an excellent model organism for studying these changes because it allows us to observe genetic and epigenetic patterns clearly. This research is important not just for understanding basic biology but also for exploring how genes are regulated and repaired."

14. References: LORENZ, A., & PAULO, S. J. (2022). GENE CONVERSION: A NON-MENDELIAN PROCESS INTEGRAL TO MEIOTIC RECOMBINATION. HEREDITY, 129, 56-63. P. JANE YEADON, HIROKAZU INOUE, FREDERICK J. BOWRING, KEIICHIRO SUZUKI,DAVID E. A. CATCHESIDE, DNA REPAIR AND RECOMBINATION, CELLULAR AND MOLECULAR BIOLOGY OF FILAMENTOUS FUNGI, 10.1128/9781555816636.CH8,(96-112), (2010). LEBLON, G. (1972). MECHANISM OF GENE CONVERSION IN ASCOBOLUS IMMERSES.II. THE RELATIONSHIPS BETWEEN THE GENETIC ALTERATIONS IN B1 OR B2 MUTANTS AND THEIR CONVERSION SPECTRUM. MOLECULAR AND GENERAL GENETICS, 116(4),322-335. HOWELL WM, LAMB BC. TWO LOCALLY ACTING GENETIC CONTROLS OF GENECONVERSION, CCF-5 AND CCF-6, IN ASCOBOLUS IMMERSES. GENETICALLY RESEARCH. 1964; 43(2):107-121. DOI:10.1017/S0016672300025830 WIKIPEDIA.COM RESEARCH GATE.COM 13

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