Some genes are dominant and some are recessive. Dominant genes override recessive genes regardless of which parent it’s inherited from. Some genes that simply aren’t compatible with each other are altered during fertilization. These altered genes are called mutations. Some are beneficial, some are harmful, but most are benign. Some genes only come from the Mother, which would be the genes for the mitochondria. While some will only come from the father, which would be the genes for the nucleus.
As for X and Y chromosomes. The X chromosome contains a lot of info you need in order to live while the Y chromosome just codes for what makes a being male. If you have a defective gene in your X chromosome and are male, chances are that it’s going to present itself. If you’re female, it depends on if that gene is dominant. One notable case is the genes for the cones in your eyes. They reside in the X chromosome and sometimes one of those genes has mutated. If you only have the mutated version you may be unable to see some colors. As [email protected] pointed out, this has advantages and disadvantages.
Disclaimer: I’m going by what I remember from high school biology. If I made an error, then please correct me.
EDIT: Corrected my wording in regards to colorblindness.
I didn’t mean to imply it was bad. I’ll reword my comment.