Notes: Types of Reproduction
***Key Idea: Genetic information is passed from
parents to offspring through CHROMOSOMES.
We have to get the chromosomes from the
parent cell the new cells that are being
produced.
In ASEXUAL reproduction, ONE organism divides in
two and makes an EXACT COPY of itself. This is
essentially MITOSIS.
Ex. Budding in yeast
Ex. Amoebas
Pros : NO ENERGY used to get together with
another organism.
Cons  : Only ONE parent contributes genes.
Sexual Reproduction: Meiosis
In SEXUAL reproduction, TWO organisms must
come together to create an offspring that is
genetically DIFFERENT than either parent.
Pros  : Genes from BOTH parents contribute to
offspring.
Cons : Must USE ENERGY to get together with
another organism.
To reproduce sexually, the organisms must first form
“gametes.” Cells of the body have two copies of sets of
chromosomes. Gametes only have one set. Why?
DIPLOID cells have two sets of chromosomes. We
represent this as 2n.
HAPLOID cells have one set of chromosomes. We
represent this as n.
Haploid
Diploid
In humans, the MALE gamete is the SPERM.
The FEMALE gamete is the EGG.
The sperm swims up the female reproductive tract and
FERTILIZES the egg.
The egg and sperm together is called a ZYGOTE
The ZYGOTE then divides by MITOSIS to form a multicellular
(many-celled) organism. Mitosis is just plain old cell
division.
Egg and Sperm!
Fertilization
Fertilization
The process of forming a gamete is called
MEIOSIS.
Steps of Meiosis
1)
2)
3)
4)
Replication
Pairing up of homologous chromosomes.
First division
Second division
Mitosis
Cell divides
once. You get
two cells
identical to the
original. Each
have two
copies of each
chromosome
Two cell divisions. You get four cells
that are genetically different than
the original cell. Each have one
copy of each chromosome.
Meiosis
2) Pairing up of homologous chromosomes.
o HOMOLOGOUS CHROMOSOMES are both sets of
chromosomes.
o Ex. Both copies of chromosome 12
o ***Genetic material is exchanged or shuffled between
the homologous chromosomes in a process called
CROSSING OVER. This produces the NEW
combinations of traits that were not seen in either
parent.
Homologous Chromosomes
Homologous Chromosomes
Crossing Over!
3) First division- Result is two haploid cells with
replicated chromosomes.
4) Second division- Result is 4 haploid cells with
unreplicated chromosomes. (Result is the egg
or sperm).
Mitosis
Meiosis
(asexual) (sexual)
# of divisions
# of cells produced
sets of chromosomes in
cells produced
1
2
2 (cells are
diploid or 2n)
2
4
1 (cells are haploid or
“n”)
type of cells it occurs all cells
in
homologous
no
chromosomes pair up?
reproductive tissues
only
yes
genetic variety of
offspring
genes are shuffled
during crossing over,
same as parent
cell