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It does absolutely nothing for your current character, at least not more than sleeping during the night normally does. If you make more than one gene, the later genes will replace the existing gene file for that character. Really, the primary benefit of baby-making is the inheritance of inventory. A very commonly recommended strategy for a new player is to start with an "easy" class like Warrior, that can plow through the early game and stock up stuff to pass on to a child who is of a much harder class. One interested in playing classes like a Wizard or Pianist or Tourist might consider this strategy to make it not as much of a punch-to-the-face for a first play.
There are limits, as explained in the article:
No Kitty Banks, so no passing on gobs of ludicrous early game fortune
No Deeds, so no inheriting very nice properties
No Figurines/Cards, these aren't baseball cards you can just pass on to your kid
No small medals/music tickets, as these are basically alternatives to cashmonies
No precious items. This is the big one, as it includes all pre-generated artifacts, diaries, most goods from Miral and Garokk's Workshop, Statues, fusion-made high potions, and about any kind of quest prize consumable that directly improves your stats (as well as hermes blood).
That is a fair much, but then what can you pass on? Your only limit is your weight capacity and your inventory limit (which is about 12 pages). Here's some advice on what to think on.
Almost any item you can wish for. Seven league boots, vindale cloaks, astral light pens, secret experience of Kumiromi... basically you can save your new game a lot of wish usage by having this stuff already prepared.
For that matter, rods of wishing can be passed on if you choose to save them up. Rods of domination can also be handy to pass on.
Piles of useful potions: holy water, unholy water, cure corruption, evolution, descent, speed upper, acidproof and fireproof liquids, antiseptic, soda. As well, useful scrolls: vanish curse, growth, gain attribute, faith, (greater) enchant weapon/armor, flying, wonder. Having just such a major supply of these goods to start a new game can make a lot of the early game dangers much softer.
Multi-use tools like a leash, stethoscope, tamer whip, fishing rod, and pot for fusion which, while moderately easy to find, can be nice to get guaranteed early. Disguise kits may also be handy, but scrolls of incognito are much lighter to stack even if they're single use.
Extra copies of the Rachel books for the one quest. As well, unicorn horns for a later quest are also helpful.
Whatever ridiculous non-pregen artifacts you may have scrounged up in your journey is fair game. Plan not just for yourself, but your future allies as well!
The six different evolution hearts can all be passed on. Guaranteed sources of God, King, Machine, and Magic Hearts are pretty late game typically, so if you save one or two up as a parent, your child can play with the results.
Monster Balls with anything inside can be passed on to allow your progeny to have friends. High powered friends that are tens if not hundreds of levels above the starting enemy challenge. Unlike the method I'll detail next, there are essentially no penalties to these other than the 10.0s they weigh.
For a different approach, a carpenter can also make what is known as a Soul Spindle. It allows one to essentially transfer a copy of an ally. The process to use one, and the penalties to a transferred ally, are detailed in this article. While the penalties look a bit steep, this is the only way to transfer unique allies that can't be caught in monster balls, and they do retain all of their special abilities and gene-engineering results. Stat penalties can be fixed with effort, in the long run.
If you spent a good amount of time nabbing an altar of your own, you can also pass that on as well to save your descendent from having to figure how to haul their own.
Do keep in mind that inheritance items use the same colors as they were in the parent game. The same items in the new game will possibly be of a different color, so not only do these not auto-identify the versions for the new game, but they also will not stack with items of the same type in the new game. To this point, it's pretty helpful to do all your blessings and such ahead of time before you sleep with your mate that night.
Aside from inheriting inventory, the only other "bonus" I can think of from having actual parents is that, if your parent used the Secret Treasure of Lomias (which is randomly dropped by Lomias the Messenger from Vindale, the jerk who kills a beggar and tries to feed you it in the game's beginning), then you will have the Beggar's Pendant artifact in your inventory to start. Thievery protection and the Charisma boost are actually pretty nice to start, and unlike the inherited goods you do not need to use a Deed of Heirship to acquire the pendant.
