Video Transcript
The diagram shows a basic outline
of the process of fertilization. After fertilization, a zygote
forms. The zygote shown in the diagram has
four cells. How many chromosomes will be in the
nucleus of each of these cells?
Humans reproduce by sexual
reproduction. During this process, a biological
female and a biological male both produce sex cells, which are also known as
gametes. The female gamete is called an egg
cell or ovum, and the male gamete is called a sperm cell. These gametes each contain 23
chromosomes in their nuclei, which is half the number of a regular body cell.
Next, one egg cell and one sperm
cell join together in a process called fertilization. During fertilization, the nucleus
of the sperm cell combines with the nucleus of the egg cell. This produces a new cell called a
zygote. Because the zygote has both sets of
chromosomes from the two gametes in its nucleus, it has 46 chromosomes
altogether.
Once the zygote has formed, it
undergoes cell division so that it can grow. It’s this process of cell division
that causes the ball of four cells that you see here to eventually develop into a
human baby. Every time a cell divides in this
way, it produces genetically identical daughter cells, which therefore also have 46
chromosomes in their nuclei. We have therefore determined that
the nucleus of each cell of the zygote will contain 46 chromosomes.