Is there a specific reason that the letter Y is used as the symbol for the male chromosome and X is used for the female chromosome?
The first inkling that sex chromosomes were unique from all other chromosomes came from experiments conducted by German biologist Hermann Henking in 1891… Henking saw that some wasp sperm cells had 12 chromosomes, while others had only 11. Moreover, while observing the stages of meiosis that formed these sperm cells, Henking noticed that the mysterious twelfth chromosome looked different from all the others. He thus named this chromosome the "X element," to represent its unknown nature.
The Y chromosome was identified as a sex-determining chromosome by Nettie Stevens … during a study of the mealworm Tenebrio molitor … Stevens proposed that chromosomes always existed in pairs and that the Y chromosome was the pair of the X chromosome discovered in 1890 by Hermann Henking … Stevens named the chromosome "Y" simply to follow on from Henking's "X" alphabetically.
I know that this is not the most reputable source, but it does cite a couple of books. Take it as it is. Keep in mind that all human chromosomes, even the Y chromosome, appear as X shaped when replicated and condensed. The Y chromosome is quite acrocentric and so the short arms may appear to be one, but they're not.
During metaphase, all chromosomes look like an
X with the exception of the chromosome
Y. See below
Y then? Well, according to wikipedia, just because the letter
Y follows the letter
X in the alphabet.
Note that many species don't have sexual chromosomes and note that in many species, the
Y-looking chromosome is present in the female but not in the male. In such case we call this
W and we call the
Z. Very likely this post will interest you.