Another helpful resource, although very much oriented to knitters and what’s available in the USA only, is https://yarnsub.com/.
If the pattern calls for a specific yarn, and they have it listed (even discontinued yarns), this site can give good guidance on what yarn could be substituted.
The article suggests that the environment plays a significant role in gasturlation, especially the chemistry.
If identical twins develop in the same uterine environment, there would be greater likelihood of the same genes expressing.