Fertilisation

Fertilization Process

Fertilization is the process by which male and female gametes (sperm and ovum) fuse to form a zygote.

Steps of Fertilization

1. Semen release: During sexual intercourse, the male ejaculates semen containing sperm from the testes.
2. Sperm journey: The sperm travels through the vas deferens to the urethra and is introduced into the female's vagina.
3. Ovum release: The female releases an ovum from the ovary into the fallopian tube.
4. Fusion: If a sperm meets the ovum in the fallopian tube, they fuse to form a zygote.
5. Prevention of multiple fertilizations: Once one sperm fuses with an ovum, the fusion of other sperm is prevented, ensuring that only one sperm fertilizes the ovum.
6. Embryo development: The zygote grows and forms an embryo, which then travels down the fallopian tube to the uterus.
7. Implantation: The embryo implants itself in the uterine wall where it begins to grow and develop into a fetus.

Fertilization process

Fertilization Leading to Multiple Embryos

Normally, a female gives birth to a single child per pregnancy. However, in some cases, a female can give birth to two or more children during a single pregnancy. These children are called multiples.

Twins

Twins occur when a female gives birth to two children in a single pregnancy. They can either be identical or fraternal.

Identical Twins

• Formation: Identical twins result from the division of a single ovum fertilized by a single sperm.
• Process: After fertilization, the fertilized egg splits to form two zygotes.
• Characteristics: These twins share almost identical genetic material, including sex, and will often look alike. They develop in the same uterus and share a placenta.

Male identical twins

Female identical twins

Fraternal Twins

• Formation: Fraternal twins arise when two separate ova are fertilized by different sperm.
• Process: Each ovary releases an ovum, and each is fertilized by its own sperm.
• Characteristics: The zygotes implant independently in the uterus and grow in their own placentas. Fraternal twins do not necessarily resemble each other and can be of different sexes (one male and one female, or both male or both female).

Fraternal twins