eli5: if you inherit 50% of your genes from your father and 50% from your mother, what stops you from getting two of the same gene, and missing one? also why do siblings look different?

Question

eli5: if you inherit 50% of your genes from your father and 50% from your mother, what stops you from getting two of the same gene, and missing one? also why do siblings look different?

In: Biology

Answer 1

There are 23 pairs of students (46 kids) in one classroom A and another 23 pairs in different classroom, B.

you go to the first pair in A and randomly pick one. you go to the first pair in B and randomly pick one. the chosen two form a new pair and go sit in Classroom C. go back to A and B and repeat for the second pair, third pair, fourth etc.

when you are done you will have 23 pairs of students in classroom C, 50% from Classroom A and 50% from Classroom B. but the namelist would be quite unique.

because if you reset (tell everyone to go back) and go make a new Classroom C you will not get the same name list, because there were a sequence of 23 random selections. the unique name list in the new classroom is what makes a new person’s DNA unique even if they came from the same parents.

identical twins are different. once Classroom C is defined, it gets copied directly into Classroom D so the name list and thus DNA is identical.

if you mess up and accidentally pick three people per step or miss a pair, that new class will probably not even start or may start but be cancelled later on (no embryo, or spontaneous abortion). sometimes messing up can still work and you end up with deformities or something like Down Syndrome.

if one of the classrooms has a bad student (gene disease, mutation), there is a chance that he or she can be helped by their new partner and the pair can still work (recessive mutation). but it won’t be great if the new partner also has the same recessive mutation. if he or she is particular bad then no good partner can help and the new pair will be bad regardless (dominant mutation). good or bad is subjective. this explains why mutations sometimes show but sometimes only get carried.

is it possible that you can do Classroom C, reset and make Classroom D with the same name list by chance? it is always possible, except I didn’t mention that each chromosome (pair of students) can have around 1000 genes. so the closer analogy would be that each student in this experiment has 1000 pets with unique nicknames each and you are actually making a 20+ thousand pair pet name list instead of 23 pairs.