How does the chance of a coin landing on each side compare to the chance that a gamete cell will receive a particular gene at meiosis?

The chance of a coin landing heads or tails is 50% for each individual time. It doesn't matter what the previous throws resulted in. If you flip a coin ten times you can get ten heads, but the probability is still 50% for each toss. The same holds true with gametes. The probability is 50% at the production of each individual cell.