Meiosis
introduction
CSCOPE
Unit 08
Lesson 02
Chromosomes
What is a chromosome?
 A piece of coiled DNA
How many chromosomes do
human cells have?
 46 (in non-sex cells)
Do ALL humans have the same number of
chromosomes in their cells?
 YES! (Except people with genetic disorders causing
extra chromosomes or
missing chromosomes)
Where did the 46 chromosomes come
from?
Turn to a friend and
discuss…
If we get our
chromosomes from our
parent, why do we not
have a total of 92 (46 from
mom and 46 from dad)?
How does each parent
manage to only give 23
chromosomes to their
child?
So…
YOU were made from one cell from
your mom and one cell from your
dad. So, how is it the same?
Shouldn’t you have double the
number of chromosomes?
 No, the number is the same because the
egg and sperm cells only have half the
number of chromosomes, so when they
combine they have the full 46.
SO, sex cells have how many
chromosomes?
 23 chromosomes
Sex Cells -- gametes
How are gametes (sex
cells) formed, if they only
have 23 chromosomes?
 Through a process called
MEIOSIS
Meiosis is similar to
mitosis but has some
differences.
Mitosis — quick review
Four Phases:
 Prophase
 Metaphase
 Anaphase
 Te l o p h a s e
DNA replication happens before
mitosis during the synthesis phase
of interphase.
Mitosis — quick review
Meiosis
Embed animation of meiosis here.
Mitosis vs. meiosis—primary
difference
 Mitosis results in…
Two IDENTICAL daughter cells—no genetic
diversity
 Meiosis results in…
FOUR daughter cells—that are different
from parent cells, resulting in genetic
diversity