The human life cycle involves two types of cell divisions: mitosis and meiosis. 386
19.2 Mitosis
Mitosis, nuclear division in which the chromosomal number remains constant, is involved in growth and repair. 387Cytokinesis divides the cytoplasm and organelles between the daughter cells. 389
19.3 Meiosis
Meiosis, nuclear division in which the chromosomal number is reduced by one-half, is involved in gamete production. 390
19.4 Chromosomal Inheritance
Normally, humans inherit 22 pairs of autosomes and one pair of sex chromosomes for a total of 46 chromosomes. 395Normally, males have the sex chromosomes XY and females have the sex chromosomes XX. 395Abnormalities arise when humans inherit abnormal chromosomes or an abnormal number of chromosomes. 396-98