The 23rd pair is an exception and determines gender. The 23rd chromosomal pair differs according to whether you're a male or a female. Males have an X and a Y chromosome, while females have two Xs for this 23rd pair of chromosomes. Every female gets one X chromosome from her mother and one X from her father. Every male gets an X chromosome from his mother and a Y from his father.
Y chromosomes are unique to males and, in fact, determine maleness.
Autosomal dominant conditions require only one mutation to show themselves. They also mean that the condition caused by the mutation can occur even if only one of the two paired autosomes carries the mutation. It's a way of saying that the mutated gene is dominant over the normal gene. In autosomal dominant disorders, the chance of having an affected child is 50 percent with each conception. Autosomal recessive conditions require two mutations to show themselves.