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Chromosomal disorders may be due to abnormalities of chromosome number or structure and may involve autosomes or sex chromosomes. Somatic cells are diploid, with a complement of 46 chromosomes, whereas gametes (ova and sperm) are haploid, with only 23 chromosomes following reduction division in meiosis. Numerical abnormalities that involve the gain or loss of one or more chromosomes are known as aneuploidies. The traditional approach to studying chromosomal anomalies involved karyotype or fluorescent in situ hybridization analysis. However, in recent years the development of array comparative genomic hybridization (or microarray) has been developed and is becoming the primary genetic tool in examining chromosomes for abnormalities of chromosome number (aneuploidy) and structure (deletions/duplications/inversions). This chapter reviews the common chromosomal abnormalities including Down syndrome and Turner syndrome, and their dermatological manifestations.
Keywords gene, chromosome, ploidy, trisomy, ploidy, fluorescent in situ hybridization, FISH, karyotype, microarray, syndrome