o = child with original gene
M = child with mutated gene
Mutant parent's family #1: o o o M o o o o M M = 3 mutant children
Mutant parent's family #2: M M o M o o M o o o = 4 mutant children
Mutant parent's family #3: o M o o M o M o o o = 3 mutant children
Mutant parent's family #4: M o o o M o o M M M = 5 mutant children
Mutant parent's family #5: o o M M M o o M o o = 4 mutant children
Mutant parent's family #6: M M M M o o M M o o = 6 mutant children
Mutant parent's family #7: M o M M M o o M o o = 5 mutant children
Mutant parent's family #8: o o M o M o M o o M = 4 mutant children
Mutant parent's family #9: o M o o M o o o o M = 3 mutant children
Mutant parent's family #10: o M o M M M M M M M = 8 mutant children
Out of 100 children, 45 were mutants. Pretty close to 50% odds per child, wouldn't you say? In fact, if it wasn't for that last outlier family the results would've been 41% mutants instead of 45%. Maybe the mutation was slightly harmful! LOL!
3. that the duplicate gene gets spread through the species at chances of 50% survival at each generation (note no selective advantage since the gene is just a duplicate at this point).