In understanding their application to forensic casework, the
unique inheritance pattern of both chromosomes needs to be
considered. Whereas with the autosomes, one chromosome of
each pair from both the mother and the father is passed on to both
male and female offspring, the X chromosome is passed from both
the mother and the father in female offspring, while male offspring
receive only one X from the mother. The Y chromosome, present
only in males, is passed down in its entirety from father to son, and
the alleles combine to form a profile known as a haplotype.
Therefore, female offspring have two X chromosomes (one from
the mother and one from the father) and male offspring have one
X chromosome (from the mother) and one Y chromosome (from
the father).