Embryology for K12 Students
© Dr Mark Hill (2011)
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, it then begins to divide
2, 4, 8, 32, 64, 128 cells and so on. This cell division occurs initially
without growth, so each division results in more smaller and smaller cells.
This process of fertilization occurs in all animals and plants that have
a male and female. (Plants cannot move, how do they fertilize their eggs?)
More? Year 7-12 Detailed Embryology Notes-
Cells in the embryo have different names from those in the adult.
This is because they are special cells that only occur in the embryo, they divide and gradually change into different types of cells with new names.
Click here to Go to Week 2
Lets see what happens to this ball of cells.
- This 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 300-400 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.
- egg- the cell from the mother
that contributes half the genes of the embryo.
- fertilization- A
process where a single male (father) and female (mother)
cell are joined together.
- genes- information in the
cell that gives it rules on how to grow and what type of
cell to become. This information is stored in DNA in the
cell nucleus. (more?
see Advanced note)
- sperm- the cell from the
father that contributes half the genes of the
- uterus- the space within
the mother where the embryo grows. It also grows when the
embryo does and has lots of blood to feed the embryo and
strong muscles in its walls for childbirth.
- zygote- The first cell
formed after fertilization.
Advanced note - a few genes
are also located in each cell outside the nucleus, in
mitochondria (mitochondrial DNA) which are involved in
cellular respiration. These mitochondrial genes are always
inherited from your mother (the egg) not your father
Quick Movie Links
Movie of Human Embryo Growth (this
shows a human embryo growing, all images are to scale)
Movie of Limb Growth(this shows development
of the human arm from bud to paddle, to hand with arm)
Movie of Mouse Embryo Growth (this
shows a mouse embryo growing)
Movie of Rotating Embryo(this shows an early
embryo from all angles)
All Moviesthis shows many different ways
of looking in at changes in different embryos.
UNSW Embryology ISBN: 978 0 7334 2609 4
UNSW CRICOS Provider Code No. 00098G