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#gene conversion

3 public questions tagged with this topic.

Linkage Mapping and Tetrad analysis

Gene conversion is detected when tetrad shows

Canonical meiosis predicts 2:2 segregation within tetrad for heterozygous marker reflecting equal replication of alleles. Appearance aberrant ratios 3:1 or 1:3 and even more extreme 4:0 or 0:4 signifies gene conversion where heteroduplex DNA formed during recombination repaired nonreciprocally, replacing one allele with other via mismatch repair bias. Conversion tract copying during homologous recombination intermediate repair converts markers asymmetrically, producing excess one parental allele over other. Detection possible only when all four chromatid products recovered together, providing molecular evidence recombination and repair mechanisms operating during meiosis.

Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 5: Gene Conversion Detected by 3:1, 4:0 Tetrad Ratios

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Recombination

SDSA pathway mainly results in

Synthesis-dependent strand annealing represents predominant mitotic homologous recombination pathway designed to avoid crossovers. After limited invasion and extension of one 3' end using donor chromatid as template, polymerase delta synthesizes short tract, then disrupted D-loop releases nascent strand through action of Mph1, Srs2, RTEL1, or FANCM helicases, restoring donor duplex unchanged. Dissociated strand anneals to second broken end, allowing fill-in synthesis and ligation without formation of stable double Holliday junction. Genetic markers flanking break remain parental configuration, thereby generating only non-crossover recombinants, critical for genome stability.

Ref: NCBI Bookshelf, Biochemistry, SDSA Pathway Results in Non-Crossover Products

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Recombination

Non-reciprocal homologous recombination results in

Non-reciprocal homologous recombination leads to gene conversion, phenomenon where heteroduplex formed between polymorphic parental duplexes contains mismatched base pairs subject to mismatch repair that can correct either direction. If repair copies information from one allele converting other to same sequence, one allele replaces another without reciprocal product, producing 3:1 segregation instead of 2:2. Mechanism involves double-strand break repair with synthesis-dependent strand annealing. Gene conversion underlies concerted evolution of ribosomal DNA arrays, antigenic variation, and loss of heterozygosity driving tumor suppressor inactivation in somatic cells.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 12: Gene Conversion from Non-Reciprocal Recombination

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