You flat out shouldn't be mating mice unless you have the genetics and are ready for it.
Genetics are tricky and ever species has LETHAL genes and mutation that should never be mixed because of hundreds of reasons.
Breeding mice together doesn't mean your a breeder.
It just means you let nature happen in a controlled environment.
A breeder a has a goal they work for to better the species they breed. Do you?
Or do you just want to breed cute mice and watch the magic?
Im sure youve heard it before but there enough pets in this world that are "cute" and "never bite!" but you need to hear it again.
There are few that live much longer than expected or dont have a genetic disease their species is known for. Or die from old age.
So tell me, do you know if your mice will live up/past 2 years?
Do you know the likeliness of them having cancer or passing it down to their generation?
Do you know if they are Lethal Yellows or just Argentes?
Saying your prepared doesnt mean when their old enough you give them away,
it means when the mother is in agony because a head or a body part of the pups is stuck in the birth canal,
you do everything possible to save her. Including paying that $700 vet bill even if she dies after all that work.
It means retiring the female at right ages and calculating that colour and coat is not even the tip of the iceburg.
It means staying up late after work or school trying to decided to breed or not to breed.
It means scouting the area and deciding not to breed because "this area has too many mice already, ill wont be helping anyone even if they are genetically sound mice.".
To answer your questions, Yes, gender is semi random.
A friend and well educated mouse breeder has had a number of litters just boys and just girls.
Yes the genders are mostly random unless youve had several litters with one pair
(should NEVER happen, females can only have two litters not back to back before it becomes a strain),
even then you can only do a rough guess at the genders. You still may be way off too.
Though you say youve read you need to study GENETICES, GENOTYPES AND PHENOTYPES more.
The albino gene is recessive. It takes TWO copies from each parent to have Albino pups.
If you Black has Albino pups per say, somewhere along his lines there was an Albino parent and his mate also has an Albino gene.
There are many genes your mice could be carrying without you knowing.
Phenotypes are sometimes hard to pin, this is why usign and knowing exact Genotypes is more than needed.