You are correct it is genetics. Genetics make most plants green, some other factor, sometimes its a virus causes them to become variegate. Sometimes it is in the plants genes like blue eyes, but not all the time. When a variegated plant is starting to show solid green leaves it's called reversion. The chances are the green parts will grow faster and bigger than the variegated part, to a point that there is very little left that is variegated after many many months or years. The parts that are variegated will stay variegated. That will not change. If you take a baby from the green side the chances are that baby will be solid green and always be green. In some cases they will grow at the same speed or perhaps the variegated on a rare chance might grow faster, but odds are really against this. The solid green leaf has more green to capture more light to grow bigger. The white part lacks chlorophyll, so it is unable to absorb the sun's rays. Many variegated plants would never survive in the wild. The next time you are near a natural area, you will probably not find any plants that are actually variegated. Humans like variegated plants, so we breed lots of plants with variegation.