Isogamy is a form of sexual reproduction that involves gametes of similar morphology (similar shape and size), differing in general only in allele expression in one or more mating-type regions. ... In all cases, fertilization occurs when gametes of two different mating types fuse to form a zygote.

Isogamous cannot be a feature of internal fertilization
Internal fertilization is a reproductive strategy in which the fusion of gametes occurs inside the body of one of the individuals involved. In this process, the male gamete typically needs to reach the female gamete for fertilization to occur.

Isogamous
- Isogamy is a type of sexual reproduction in which both gametes are similar in size and structure.
- In isogamous organisms, there is no distinction between a motile male gamete and a non-motile female gamete.
- Since isogamous organisms do not have distinct motile and non-motile gametes, they do not require the specialized mechanisms associated with internal fertilization, such as the transfer of sperm to the female reproductive system.

Oogamous
- Oogamous is a type of sexual reproduction in which the female gamete (egg) is larger and non-motile, while the male gamete (sperm) is smaller and motile.
- This type of reproduction is commonly associated with internal fertilization, as the motile male gamete needs to reach and fertilize the non-motile female gamete inside the female reproductive tract.

Motile male gamete
- Having a motile male gamete is a common feature of internal fertilization.
- The ability of the male gamete to move towards the female gamete increases the chances of successful fertilization, especially in environments where the gametes need to travel through complex reproductive structures.

Non-motile gamete
- In internal fertilization, the female gamete is often non-motile, as it remains in place within the female reproductive system awaiting fertilization by the motile male gamete.
- The non-motile nature of the female gamete allows for the efficient and controlled fertilization process that occurs inside the body.
In conclusion, isogamy, which involves similar-sized gametes that are not specifically motile or non-motile, cannot be a feature of internal fertilization, as it does not require the specialized mechanisms associated with the fusion of motile and non-motile gametes inside the body.