Final answer:
In XX, XO sex determination, males carry a single X chromosome, represented as 'XO,' where 'O' indicates the absence of a second sex chromosome, not an actual 'O' chromosome. The correct option is a.
Step-by-step explanation:
In the XX, XO sex determination system, males have a single sex chromosome, which is an X chromosome. The correct answer to the question is 'a. a single X chromosome.'
This sex determination system does not involve a Y chromosome as seen in humans and other mammals; instead, the absence of a second sex chromosome is represented by 'O' which stands for 'null' or absence of a sex chromosome.
Therefore, in this system, females are XX, having two X chromosomes, while males are XO, where 'O' signifies the lack of a second X or Y chromosome.
To clarify, the XO terminology is somewhat misleading because males do not have an 'O' chromosome; 'O' simply indicates that there is only one X chromosome, without a corresponding second sex chromosome. The correct option is a.