1. Fertilization and Development

2. Gamete formation Before sexual reproduction can occur, both male and female gametes need to be produced. They are formed through meiosis, which means the gametes will be haploid in chromosome number (n). In humans each gamete will contain 23 chromosomes.

3. Spermatogenesis The formation of sperm cells by Meiosis. The formation of sperm cells by Meiosis. Results in 4 sperm cells. Results in 4 sperm cells.

4. Oogenesis The formation of egg cells by meiosis Results in one egg cell and three polar bodies. Polar bodies, which are much smaller than egg cells, are broken down and reabsorbed.

5. Fertilization The union of the sperm and the egg cells. Occurs in the fallopian tube (oviduct) Results in the formation of a zygote. A zygote is a single cell that has a diploid number of chromosomes.

6. Cleavage The zygote begins to divide by a type of mitosis called cleavage. In cleavage the cell undergoes many mitotic division with no increase in size. Cleavage continues and the zygote becomes a hallow ball of cells called a blastocyst or blastula.

7. Blastula The blastula, also called a blastocyst or blastosphere is a hollow fluid-filled ball of cells. All the cells are exactly the same

8. Gastrula In this stage, the different germ layers begin to form. The cells begin to differentiate into many types of cells. These cells each utilize different parts of the genetic information in the DNA

9. Implantation The developing gastrula, now known as an embryo implants itself into the uterine wall. At the spot of implantation the placenta forms. The placenta attaches to the embryo by means of the umbilical cord. The lining of the uterus is called the endometrium.

10. Ovulation to Implantation diagram

11. Early development It is in the first trimester (3 months) of development that the embryo, then fetus are most susceptible to drugs/alcohol/environmen tal changes. During this stage all the organs of the body begin to form. At around 8 weeks, the embryo is now a fetus.

12. Second trimester The fetus begins to resemble a baby during this stage. Facial features form, hormones guide the development of both boys and girls and the fetus is able to see and hear. The fetus begins to become active(kicking).

13. Third trimester During this trimester, the fetus puts on a lot of weight. At 6 months the fetus is able to survive outside the womb in an incubator. The lungs are the last organ system to fully develop

14. Childbirth As the due date nears, the fetus changes position in the womb. The fetus moves into what is referred to as the birthing position, which is head-down.

15. Birth and nursing After giving birth, the mother’s breast will begin to express milk. The action of the baby feeding stimulates the mom’s endocrine system to continue to produce progesterone and prolactin. During breastfeeding the mother does not menstruate.