Absolutely. The "gravity" is merely the ratio of water to sugar (malt extract or whatever you use as a fermentable). So by adding more water, you've diluted the mixture and lowered the gravity.
If you had 1.045 before dividing, and divided equally, then your gravity would be 1.022 in each. That is a very "small" beer and will very likely taste thin and watery, and not very bitter or hoppy.
One of the major aspects of brewing is getting the gravity right. Boiling too long, or too short, mash efficiency, grain absorption, etc. all play into the variables that give a certain gravity. When you use extract a lot of this is moot because extract has a very determinable amount of sugar in it. It's very easy to measure. So if you can measure the right amount of extract and water, and boil for a certain length of time, you should hit your gravity pretty good.
For a 1 gallon batch I would be tempted to make a slightly stronger (higher gravity) wort and then dilute to the gravity you really want and fill the fermentor with it. If there is a little extra, don't sweat it. If you end up a little short on volume, don't sweat it. Try to get the gravity as close as you can to the recipe and don't worry about whether or not you get a perfect amount of beer.
