Castration of an animal is forbidden to Gentiles (according to most opinions) so a Jew cannot tell him to do so. If he does he is forbidden to eat that animal. But if the gentile has already castrated the animal it is permitted for a Jew to eat that animal.
The Shulchan Aruch (Rabbinic Authority) Even Haezer 5,14 says:
אסור לומר לכותי לסרס בהמה שלנו. ואם לקחה הוא מעצמו וסרסה, מותר. ואם הערים ישראל בדבר זה, קונסין אותו
It is forbidden to tell a Gentile to castrate an animal, but if the Gentile castrated it himself without consent form any Jew it is fully permitted to have benefit from. But if the Jew told the Gentile to castrate the Animal for him he cannot benefit from the animal as a penalty.
Chelkas Mechokek (Rabbinic authority) elaborates:
ישראל אחר מותר לאכול אף על גב שהוא בכלל תעבתי לך מ"מ מדאסור לגבוה ש"מ להדיוט שרי מרדכי פ' ש"ש וישראל שסירס או שסירס העכו"ם בשבילו משמע דאסור לאכול ממנו
We only punish him since he told the Gentile to castrate the Animal or castrated it himself he cannot eat it, but we don't punish other Jews that were not involved in telling the gentile to castrate the Animal i.e they can eat those castrated animals as long as it was Slaughtered properly.
Kilayim: A Gentile is not commanded regading cross breed of seeds .
Rather a Gentile is only commanded regarding crossbreeding trees for fruit, and cross breeding animals species. Rambam Melachim 10,6:
מִפִּי הַקַּבָּלָה שֶׁבְּנֵי נֹחַ אֲסוּרִין בְּהַרְבָּעַת בְּהֵמָה וּבְהַרְכָּבַת אִילָן בִּלְבַד
A Noachide is commanded not to crossbreed animals and trees
So since a gentile can make genetically modified seeds and feed his animals, those animals are fully permitted for a Jew to buy as no transgression has happened.