Speaking of DNA sexing... I learned recently that birds have sort of an opposite sex determination system than humans do.
Human gender is determined by the presence of sex chromosomes X and Y, XX (female) or XY (male) and males essentially determine the gender of the progeny. There are variants of this as well when people lack a sex chromosome or have an extra chromsome. (XO = Turner Syndrome, Klinefelter's Syndrome = XXY ... etc) And the presence of a certain gene called SRY will make a genetic female human develop male characteristics.
Apparently birds have a system that works in the opposite way, called a ZW system. The letters ZW are apparently used so that people do not confuse it with the XY system. Apparently female birds determine the gender of the progeny. Female birds are ZW, while males are ZZ. I imagine they use these to determine the sex of birds when birds are tested.