The correct answer is option 4, XY. In humans, sex is determined by the presence of either an X or Y chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The Y chromosome contains the SRY gene, which triggers the development of male reproductive structures during embryonic development.

Option 1, XO, is the chromosomal combination found in individuals with Turner syndrome, a condition where females have only one X chromosome. This leads to various physical and developmental issues.

Option 2, XXX, represents a chromosomal abnormality called Triple X syndrome. It occurs in females who have an extra X chromosome. This condition may cause physical and developmental differences, but it does not determine maleness.

Option 3, XX, is the typical chromosomal combination found in females. It does not result in maleness.

Alert - correct answer should be 5: None of the above.