A different combination of allele within their genes.
1.) latitude
2.) Air mass
3.) Ocean currents
4.) Proximity to water
Crossing over can create genetic variation. Crossing over is when chromosomes cross over they give + take a part of another chromosome which can create different variation in genes.
B right atrium it receives both from the superior vena cava venea cavae
I would say A just because if your dad has a genetic disease and you mom does not have it you have about a 50 50 chance of having that disease in a perfect control that's assuming that its recessive and that your moms side does not present this disease
that's how its always been taught to me