K12 Week 1

Week 1 after Fertilization

• The first week of human development begins with fertilization of the egg by sperm forming the zygote.

Zygote with 2 pronuclei Dr S. J. DiMarzo

• The zygote is the first cell of the new embryo containing a new combination of genes from mother and father.
• The zygote is a large single cell still floating free inside the uterus.
• The zygote then begins to divide each day into 2 cells, then again into 4 cells, 8, 32, 64, 128 cells and so on.
• Cell division makes each cell smaller and smaller again.

This process of fertilization occurs in all animals and plants that have a male and female.

Question: Plants cannot move, how do they fertilize their eggs?

Facts

• The process of fertilization occurs in all animals and plants that have a male and female.
• A fertilized egg does not mean it will go on to form an embryo. Many fertilized eggs do not develop into embryos.
• In humans, usually only 1 egg is released at a time each month.
• A women will release between 300 to 400 eggs during their adult life.
• In cats, dogs and other animals several eggs can be released at once. This is one reason why these animals have many babies at once.

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Cite this page: Hill, M.A. (2024, April 26) Embryology K12 Week 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Week_1

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G