hereditary diseases caused by changes in the number of chromosomes (genomic or chromosomal mutations). These disorders occur as a result of mutations in the germ cells of one of the parents. Examples of abnormalities in the number of chromosomes: Down syndrome – trisomy 21, Patau syndrome – trisomy 13, Edwards syndrome – trisomy 18. Examples of disorders of the number of sex chromosomes: Shereshevsky-Turner syndrome – the absence of one X chromosome (45 X0), Klinefelter syndrome – polysomy on X chromosomes in boys (47, XXY), polysomy on the X chromosome – trisomy, tetrasomy, pentasomy.