That's how come strait run chicks are about half boys and half girls. Now, here is the cool part. Remember that each chomosome has many genes on it. That's how come Sex-Link chicks can be told apart,boy from girl,right at hatch. The boys have color genes from both parents, and the girls have color genes only from their dad.
Hens only have ONE sex chromosome.
Hope this helps. I found one here but fear its to be to technicall. Haven't found a fun book on poulty genetics, just the basics of sex-link chicken genetics. I'd like to wade through it. Genetics is so fascinating.