The Torah commands in Parashat Kedoshim (Vayikra 19:19), “Behemtecha Lo Tarbi’a Kil’ayim,” which forbids mating a male animal and a female animal from different species. Crossbreeding is forbidden regardless of whether one mates two Behemot (domesticated animals) from different species, or two Hayot (non-domesticated animals) from different species. This prohibition applies also to mating land creatures with sea creatures.
The Sefer Ha’hinuch explains that G-d forbade crossbreeding because He created the world with the precise species with which He wanted the world to be inhabited. The Torah tells that after the process of creation, “G-d saw everything He made, and behold, it was very good” (Bereshit 1:31). He was pleased with His creations, and does not want more species to come into existence. Therefore, He forbade creating new species through crossbreeding. The Sefer Ha’hinuch warns that G-d’s blessing is not bestowed upon new species which are created through the mating of different animal species.
Nevertheless, if one violated this prohibition and mated animals of different species, the product is permissible for benefit. If both parents’ species are kosher, then the animal they produced is permissible for consumption. There is some discussion as to how the offspring’s status is determined – whether it assumes the status of the father’s species or the mother’s species. Halacha treats Behemot differently from Hayot, and thus if a Behema is mated with a Haya, we must determine whether to regard the offspring as a Behema or a Haya. It appears from the Rif (Rav Yishak of Fez, Morocco, 1013-1103) that the product of crossbreeding assumes the status of the mother, and thus, for example, if the mother is a Haya, then the offspring is treated as a Haya.
This prohibition applies in all places, in all times, and to both men and women. One who actively mates animals of different species has violated this prohibition and is liable to Malkut. Since this violation is transgressed through committing an action, violators are liable to Malkut for their offense. If one causes the animals to mate indirectly, such as by making certain sounds, or bringing them together into the same pen, then he is guilty of violating a Rabbinic enactment, and receives Malkut for disobeying this provision.
Hacham Bension Abba Shaul (Jerusalem, 1924-1998), in one of his responsa (Or Le’sion, vol. 2, p. 141), addresses the status of fruits produced via grafting a branch of one species onto a tree of a different species. He writes that one who eats this fruit for the first time in a year does not recite the Beracha of “She’he’hiyanu,” which is normally recited when one eats a fruit for the first time that year. We obviously cannot celebrate the opportunity to enjoy something which the Torah did not want produced, and thus reciting “She’he’hiyanu” would be inappropriate. If, however, seeds from this hybrid fruit were planted, and yielded additional fruit, one who eats that fruit does, in fact, recite “She’he’hiyanu,” because planting these seeds is entirely permissible, and thus the fruit has been produced through permissible means.
Hacham Bension also addresses the question of whether one would recite “She’he’hiyanu” over such a fruit if he had already eaten that season both species from which it was produced. One might figure that this fruit is not new for the individual, since he had already eaten the two “parent” fruits. However, Hacham Bension rules that one does, in fact, recite “She’he’hiyanu” in such a case, because this fruit is considered an entirely new entity, fundamentally different from the two species from which it was produced.