Human fertilization and early development | High school biology | Khan Academy | Summary and Q&A

TL;DR

Fertilization is the process of the sperm cell fertilizing the egg cell, resulting in the formation of a zygote, which then undergoes cell division to develop into an embryo and eventually a fetus.

Key Insights

• 💁 Fertilization is the process of sperm and egg cells combining to form a zygote.
• ➗ The zygote undergoes cell division through mitosis and develops into a blastocyst.
• ❓ Development from blastocyst to embryo and then fetus occurs over several weeks.
• ❓ Viability, the ability to survive outside the womb, typically occurs around the 24th week of gestation.
• 💁 The genetic information from both parents is combined in the zygote, determining the traits of the developing organism.
• 💯 Each individual starts as one out of hundreds of millions of sperm cells competing to fertilize the egg cell.
• ❓ The similarity in early development among species indicates common ancestry.

Transcript

• [Instructor] What we're gonna do with this video is talk about fertilization and development in human beings or at least early development in human beings. And this right over here is an actual image of fertilization about to happen or happening. So this right over here is a sperm cell. One of the many sperm cells that will come from a male human... Read More

Questions & Answers

Q: What is fertilization?

Fertilization is the process in which a sperm cell from the father joins with an egg cell from the mother, resulting in the formation of a zygote that has the combined genetic information of both parents.

Q: How does cell division occur after fertilization?

After fertilization, the zygote starts to divide through mitosis. It first splits into two cells, then four, and so on, leading to the formation of a morula consisting of 16 cells. This division continues until a blastocyst with hundreds of cells is formed.

Q: What is the difference between an embryo and a fetus?

An embryo is the term used to describe the developing organism from fertilization until around the 12th week of gestation. Afterward, it is considered a fetus. The transition is not well-defined, but the 12-week mark is commonly used.

Q: When does viability occur during pregnancy?

Viability refers to the point in pregnancy when there is a significant chance of survival if the baby were to be born prematurely. It is generally considered to be around the 24th week of gestation, although there is a roughly 50% survival rate at the sixth month.

Summary & Key Takeaways

• Fertilization occurs when a sperm cell from the father comes into contact with and penetrates the egg cell from the mother, resulting in the creation of a zygote.

• The zygote undergoes cell division through mitosis, splitting into two cells, then four, and so on. After several days, it forms into a blastocyst consisting of hundreds of cells.

• The blastocyst continues to divide and develop, transitioning to an embryo, which eventually becomes a fetus by around the 12th week of gestation.