Types of Reproduction Notes
Notes: Types of Reproduction
***Key Idea: Genetic information is passed from
parents to offspring through CHROMOSOMES.
Remember that chromosomes are DNA and
PROTEIN. 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 ENEGY 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
plan old cell division.
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
(asexual)
Meiosis
(sexual)
1
2
2
sets of chromosomes
in cells produced
2n
n
type of cells it occurs
in
all cells
# of divisions
# of cells produced
homologous
chromosomes pair
up?
genetic variety of
offspring increased
NO
NO
4
reproductive tissues
only
yes
YES
Mitosis
Here are the two
chromosome #5s in a 2n
(diploid cell).
Replication occurs. Each
chromosome is copied to
prepare for division.
The cell division occurs. The
replicated chromosomes are
separated.
Homologous chromosomes
DO NOT pair. All
chromosomes line up in the
middle of the cell “single
file.”
The product is 2
cells that are
diploid (2n). This is
exactly what we
started with.
Meiosis
Replication occurs. Each
chromosome is copied to
prepare for division.
Here is one set of chromosomes.
For example, the two sets of
chromosome #5. We call the two
sets “homologous chromosomes.”
This is a diploid (2n) cell.
The first division occurs.
Homologous chromosomes
separate.
The second division occurs
and the replicated
chromosomes separate.
We now have haploid (n)
cells with replicated
chromosomes.
We now have 4
haploid (n) cells with
unreplicated
chromosomes.
Mitosis
2n diploid
cell
REPLICATI
ON
Chromosomes line
up single file in
middle of cell.
DIVISION
Meiosis
2n diploid
cell
REPLICATION
Homologous
chromosomes pair and
line up “two by two.”
Crossing over occurs to
increase genetic variety.
FIRST DIVISION
Haploid (n) cells
with replicated
chromosomes.
SECOND DIVISION
4 haploid (n)
cells with
unreplicated
chromososo