How is a fertilized egg formed?

A fertilized egg, also known as a zygote, is formed through the process of fertilization, which involves the union of a sperm cell and an egg cell. Here's a breakdown of the process:

1. Ovulation: The female reproductive system releases an egg cell from the ovary, a process called ovulation.

2. Sperm Transport: Millions of sperm cells are deposited in the vagina during intercourse. They then travel through the cervix, uterus, and into the fallopian tubes, where the egg cell is located.

3. Penetration: A single sperm cell successfully penetrates the outer layer of the egg cell, called the zona pellucida.

4. Fusion: The sperm and egg cell nuclei fuse together, combining their genetic material. At this point, the egg is now a zygote.

5. Completion of Meiosis: The egg cell was initially in a state of meiosis II (a type of cell division) but is arrested until fertilization occurs. Upon penetration by the sperm, meiosis II is completed, resulting in a haploid egg nucleus.

6. Zygote Formation: The fusion of the sperm and egg nuclei creates a single cell with a complete set of chromosomes, half from the mother and half from the father. This cell is now a zygote.

7. Cleavage: The zygote begins to divide rapidly, forming a ball of cells called a morula.

8. Implantation: The morula travels down the fallopian tube and implants in the uterine lining, where it will continue to develop into an embryo.

Key Points:

* Haploid vs. Diploid: Sperm and egg cells are haploid, meaning they contain half the number of chromosomes found in a normal cell. The zygote is diploid, containing a complete set of chromosomes.

* Genetic Diversity: Fertilization is a key process for genetic diversity, as it combines the genetic material from two parents.

* Conception: Fertilization marks the beginning of pregnancy.

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