Biotech adds genes, parenthood, polution and mechanitors to rimworld. the DLC costs € 23.49
Genes
Genes in rimworld are what makes up a pawn, up untill now all your pawns would have been baseliners who have nothing particularly exotic about them, but biotech adds special genotypes that can be found throughought the world such as wasters who thrive on polutiin and drugs, impids who are fast, potent psi casters with fire powers, hussars who are empire made super soldiers etc, you can also find gene packs with more specific uses such as acid spit or exploding on death. I also highly recommend the vanilla expanded genes from the steam workshop as it adds some truly insane additions.
Parenthood
Parenthood is the other primary way of creating pawns with varied genes and creating new pawns. Pawns who are in a relationship and have the correct means or reproduction (this may vary from geneline to genline but typically it is male + female or asexual fission) have a chance each night if they are both fertile and share the same bed to become pregnant. This will impact the pregnant pawn's capacity for work and may come with mood debuffs due to pain etc, but after 18 in game days, broken up into 3 6 day trimesters where the debuffs the pawn is subjected to will gradually get worse the baby will be born. Note that miscarraiges are possible due to malnutrition or other factors such as combat damage etc, so generally speaking make sure your pregnant pawns are not fighting on the front lines or working in hazardous enviornments, a good choice of jobs would be cutting stone bricks as anyone can do it and it has relatively few risks.The baby will have a mix of genes from both parents, note that some genes will not be inherited such as sanginophage genes, this is good and bad as if your baby becomes too genetically complex there is a chance for the cell instability trait to appear, this in short comes in varying severities and can either be you live for 10 less years with with mild risks of cancer to your life span is about 20 and your gonna be covered in tumours.
The other method of creating baby pawns is through assisted reproduction. This can be done by harvesting an ova from a female pawn using the "extract ovum for IVF" procedure in the medical tab of the pawn, a skilled doctor is recommended for this procedure, this ovum may then be fertilised by a male pawn in your colony (slave or colonist but not prisoners) this will create an embryo. which can either be implanted in a surrogate mother or a growth vat. Growth vats are used to grow embryos to babies and babies to children, note that putting a sentient creature into a vat for 18 years of their life may lead them to have some "developmental issues" and will negatively impact their stats and relationships with their parents.
The last part of parenthood is the actual raising of your children, children will wander the colony when thye are of age and do basic chores such as cleaning and hauling, time spent around other colonists and teaching assigned colomnists will improve their skills, this is to disencentivise people from making a concrete box with a food tube into it to store their children until they are of use to the colony, something something human rights on the rim.
Overall I am a big fan of the genes and parenthood system, it adds a lot of depth to the game and without it the rim feels hollow, you can completely avoid the parenting part if you like but its fun to watch your colony develop happy little families, or see what the absoulte limit of genetic tampering is before you make something truly unsalvagable.
Mechanitors are pawns who are capable of creating and controlling their own mechanoid hive. This is done by finiding the crashed exostrider on your map and calling in the mechanitor ship, inisde will be a dead mechanitor with a mech link you can have installed in a pawn along with some basic mechanoid enemies to kill. From there you can research the various tiers of mech tech by killing the mechanoid bosses and scanning their brains. This will unlock more complex mechaoids or you to create at the gestation vat. Generally they cost teel, plasteel and cores, cores can be created by scanning pawn brains, with higher elvel cores outright killing pawns in order to make them. The advantage of mechanoids is tey have no emotinal needs, dont eat but they do create polution and will need to recharge in a charging station. I wont cover each individual mechanoid as there is a lot but there is one for every basic job and several comba ones, my favourite is the centurion as it can shield nearby pawns and provide good shooting.
Despite how little I wrote about mechanitors I quite like them, they add good variety to playthroughs and can create intresting dynamics within the colony
Polution is the last main feature of biotech and it serves as an alternative way to create power and a large risk, or weapon of mass destructuion if you are creative. Polution can be created through various means but the primary one is toxifier generators or accepting waste disposal quests. Wastepacks are large chunks that will over time disolve and spread polution. Polution is bad as it will stop crops from growing, harm pawns and make them unhappy slong with drawing in insectoid infestations. So waste packs must be stored in a freezer to prevent disolving, or alternatively fired from drop pods to your enemies who will watch s 10000 pounds of nuclear run off lands in their back yard and begins to change the air from 80% oxygen to 99% carcinogencs. Note that some genelines actually gain benefits from being in polution such as wasters, so a pure polution playthrough might be a fun alternative.
Overall I am a big fan of biotech, its by far the most in depth DLC and completely tranforms the way the game plays, I only gave a briefo verview of how it works but trust me, its worth getting, I would give it a 9/10, most likely the first DLC I would say to pick up beside Royalty