To give a short excerpt from the help center, specifically What topics can I ask about? (Emphasis mine):
- Creation of elements of a world (languages, species, buildings, etc.)
- How to achieve a specified effect in a defined world, including the use of biology, technology or magic, while maintaning in-universe consistency
These are just two lines from the site to show that we welcome questions that are not about creating a whole world, but about an element of a world. And biology is an element of a world. As long as your question is answerable in the usual Q&A-style of StackExchange and you show that you are trying to build your own "world" or creature or whatever with them, instead of asking a canonical question that would be better at SF.SE, you can ask about the topics you mentioned in your question.
If you want to talk about your theories in an open-ended brainstorming style I recommend the chat. There we often have longer open discussions about topics that would not be good for the Main Site. This is also a great place to start if you are thinking about writing a question and want to get a bit of feedback on what things you should keep in mind when writing the question.
We have a Sandbox on the Meta Site. It is designed to help people who are not sure if their question is ready for the Main Site. If you have a draft you can post it there together with your intended title and the tags you want to use. People can give you feedback on that specific question and show you how to improve it.
You should wait at least 24 hours after posting a question there before it moving it to the Main Site to give users in different timezones a chance to have a look at it. People will comment and vote to show whether your question is ready for the Main Site or not.
The following are a few examples that I had in mind when reading your question to show that we welcome questions about existing "worlds", though they are not necessarily about genetics:
There are many, many more on our site. Browsing the genetics might give you an idea about this specific topic.