TABLE 13-1. Examples of Karyotype Designations Using the 2016 International System for Human Cytogenetic Nomenclature 46,XX Normal female chromosome constitution 47,XY,+21 Male with trisomy 21 47,XX,+21/46,XX Female who is a mosaic of trisomy 21 cells and cells with normal constitution 46,XY,del(4)(p 14) Male with terminal deletion (del) of the short arm of chromosome 4 at band p 14 46,XX,dup(5)(p 14p 15.3) Female with duplication (dup) of the short arm of chromosome 5 from band p14 to band p15.3 45,XY,derCi 3;14)(q 1 O;q 10) Male with balanced robertsonian translocation (der) of the long arms of chromosomes 13 and 14-the karyotype now has one normal 13, one normal 14, and the translocation chromosome. reducing the normal 46 chromosome complement to 45 46,XX,t(11 ;22)(q23;q 11l.2) Female with a balanced reciprocal translocation (t) between chromosomes 11 and 22, with breakpoints at 11 q23 and 22q 11l.2 46,XY,inv(3)(p21 q 13) Male with inversion (inv) of chromosome 3 that extends from p21 to q 13-a pericentric inversion because it includes the centromere 46,X,r(X)(p22.1 q27) Female with one normal X and one ring (r) X chromosome, with the regions distal to p22.1 and q27 deleted from the ring 46,X,i(X)(q 10) Female with one normal X chromosome and an isochromosome (i) of the long arm of the ish 22q11l.2(HIRAx2) FISH of metaphase cells using a probe for the HIRA locus of the 22q 11l.2 region, with 2 signals identified (no evidence of microdeletion) ish del(22)(q 11.2q 11l.2) (HIRA-) FISH of metaphase cells using a probe for the HIRA locus of the 22q11l.2 region, with only one signal identified, consistent with the microdeletion arr[GRCh38] 18p 11.32q23 Microarray analysis (arr), genome build GRCh38, showing a single copy gain on (102328_79093443)x3 chromosome 18 from band p11.32 to band q23 (essentially the entire chromosome), consistent with trisomy 18 arr[GRCh38] 4q32.2q35.1 Microarray analysis (arr), genome build GRCh38, showing a copy loss on the long arm of (163146681_183022312)x1 chromosome 4 at bands q32.2 through q35.1 (19.9 Mb) arr[GRCh38] 15q 11l.2q26 SNP microarray analysis (arr), genome build GRCh 38, showing homozygosity for the entire (23123715_101888908)x2 long arm of chromosome 15 cycle regulator; SNP = single nucleotide pleomorphism.
Used with permission from Dr. Kathleen S. Wilson.
which is failure of normal chromosomal pairing and separation during meiosis. Nondisjunction may occur if the chromosomes: (1) fail to pair up, (2) pair up properly but separate prematurely, or (3) fail to separate.