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Mr. Altorfer
Science
Meiosis
Section 5.3
What You Will Learn
► Explain
the difference between meiosis and
mitosis.
► Describe how chromosomes determine your
gender. (male or female)
► Explain why sex linked disorders occur in
one sex more often than others.
Asexual Reproduction
► Asexual
Reproduction- (Mitosis): One
parent cell is needed. The result is an exact
copy of the cell that you started with.
 Most of the cells in your body reproduce
in this way.
 The chromosomes are copied and then
divided into two new cells.
Asexual Reproduction
Mitosis
Mitosis results in two exact copies of the cell that we started with.
Sexual Reproduction
► Sexual
Reproduction- Two parent cells
join together to form offspring that are
different from both parents.
► Sex Cells- The cells that come from the
parents to form offspring.
 Sperm and egg cells are examples of sex
cells.
Sexual Reproduction
► Homologous
Chromosomes- Chromosomes
that carry the same set of genes.
 HINT: Imagine a pair of shoes. Each shoe is
like a homologous chromosome. The pair of
shoes represents a homologous pair of
chromosomes.
 Human Body Cells have 23 pairs of
chromosomes or 46 chromosomes.
 Human Sex Cells have half the number of
chromosomes. Why?
Sexual Reproduction
Human body
cells have 23
pairs of
chromosomes
(46 total).
Sexual Reproduction
Sperm and egg
cells have half the
number of
chromosomes.
(23 chromosomes)
Why only half?
Meiosis
► Meiosis-
The process that produces sex
cells with half the number of chromosomes.
► Human sperm cells and human egg cells
have 23 chromosomes.
► 23 chromosomes from the sperm and 23
chromosomes from the egg gives you a
complete set of 46 chromosomes.
Meiosis
As a result of
meiosis, these
cells end up
with half of
the number of
chromosomes.
Meiosis
Sex Chromosomes
► Sex
Chromosomes- The chromosomes
that determine our gender.
 Females have two “X” chromosomes.
 Males have an “X” and a “Y”
chromosome.
Sex-Linked Disorders
► Sex-Linked
Disorders- Certain diseases
or conditions are caused by genes that are
located on the “X’ chromosome.
 Examples: Color blindness, hemophilia
Sex-Linked Disorders
“A” is dominant
for normal
vision
“a” is recessive
for
colorblindness.
What gender
will be
colorblind in
this cross?