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Fig. 1 | BMC Medical Genetics

Fig. 1

From: Validation of a high resolution NGS method for detecting spinal muscular atrophy carriers among phase 3 participants in the 1000 Genomes Project

Fig. 1

Evolution of the human SMN locus. a. The human SMN1 and SMN2 genes were derived by duplication of a proto-SMN gene after the human-chimpanzee split. The yellow bar represents the only functional base change that distinguishes SMN2 from SMN1 (on chromosome 5 at position 69,372,353 in the GRCh37/hg19 reference genome) which is signified on the canonical transcript position as c.840C > T. The copy number of each gene on a single chromosome is indicated in the bracket and colon formulation [SMN1:SMN2]. A canonical SMN chromosomal locus consists of one copy of each gene in the centromere-telomere order SMN2-SMN1. A canonical homozygous genotype is represented as [1:1]/[1:1]. b. Comparison of SMN1 and SMN2 sequences on either side of the gene-defining c.840C > T base difference. c. Three categories of interlocus homologous recombination between SMN1 and SMN2 generate copy number variants of the SMN locus. 1. Recombination and exchange on the centromeric side of the SMN2-defining base; 2. recombination and exchange on the centromeric side of the SMN2-defining base; 3. interlocus gene conversion across the SMN2-defining base region, indicated with the double-arrowed line. d. Each recombination event produces two variant SMN chromosome types which are cross-referenced from panel c. Variant chromosomes are ordered by total SMN copy number

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