The developmental period during which a being grows from a single cell to an organism complete with brain and behavioral capabilities in 9 months is called

Prenatal.

Explanation:

The sexual reproduction may be defined the process of fusion of the male sperm and female ovum that leads to the formation of the zygote. Zygote is diploid in nature.

The prenatal development includes all the stages that are involved in the development of the single cell till the completion of the nine months of the fetus. The development of all organs and the process of the cell specification all occurs in the prenatal development stage.

Thus, the answer is prenatal.

Prenatal development

Explanation:

Prenatal development is the phase of growth and development in which a single-celled zygote grows into an embryo followed by the fetus and then a baby in the womb of a lady.

The process of prenatal development is very complicated which is divided into three phases:

1. Germinal phase: during the first two weeks after the conception in which the single-celled zygote develops.

2. Embryonic period: during which the zygote grows into the embryo and lasts from the second week to the eighth week.

3. Fetal period: During which the embryo grows to form a fetus which matures into a baby and is born.

Thus, Prenatal development is the correct answer.