Among living organisms, there are two
types of reproduction-asexual and
sexual.
 Each type of reproduction has
advantages and disadvantages.

Sexual Reproduction
Two parent cells join together to form
offspring that are different from the
parents.
 These parent cells are called sex cells
and are different from ordinary body
cells.
 Human body cells have 46 (or 23 pairs
of) chromosomes.
 Sex cells have only 23 chromosomes,
half of the usual number.

Sexual Reproduction

Information contained on chromosomes
determines many of our traits.
 Eye color
 Hair color
 Blood type
Sex chromosomes determine gender.
 In humans, females carry two X
chromosomes.
 Males have one X chromosome and one Y
chromosome.

Sexual Reproduction
Sex cells in females are called eggs and
carry an X chromosome.
 Sex cells in males are called sperm and
carry either an X or a Y chromosome.
 Egg and sperm combine to form either
XX (female) or XY (male).

Sexual Reproduction
The result: the offspring will carry half of
each parent’s traits. Each time offspring
are formed, a new combination of traits
is passed.
 So, sexual reproduction produces
offspring that have a different
combination of traits than their parents
and their siblings.

Sexual Reproduction

Advantage- variation among offspring
allows for adaptations and natural
selection to occur.

Disadvantage- organisms must find a
mate in order to reproduce.

sexual reproduction in plants
Asexual Reproduction

In asexual reproduction, a new organism
(sometimes more than 1) is produced
from only one organism.

New organisms have the exact same
DNA as the parent.

This is known as Mitosis
Mitosis:
Happens
in all cells
Cell division process
5 major stages
Prophase:
Nuclear envelope disappears
 Chromosomes condense – can see
sister chromatids

and centromere
 Spindle forms
Prophase:
Metaphase:
 Chromosomes
move to the
equator of spindle
 Each chromatid is attached to
spindle with centromere
Metaphase:
Anaphase:
 Centromeres
split
 Sister chromatids are pulled
apart to opposite poles of the
cell
 Each chromatid is now a
separate chromosome
Anaphase:
Telophase:
 Nuclear
envelopes (2) reform
 Chromosomes begin to uncoil
Telophase:
Cytokinesis:
 Cytoplasm
divides
 Two new daughter cells are
now separate
Cytokinesis:
Organisms can asexually
reproduce by:
 Budding-
new
organism
grows from the
parent.
 Examplesprickly pear
cactus and
potatoes.
Organisms can asexually
reproduce by:

Fission- single
celled bacteria
without a nucleus
copies its genetic
material and
divides to form an
exact copy of itself.

fission in bacteria
Organisms can asexually
reproduce by:

Regeneration-
some organisms
can grow an
entirely new
organism from a
broken piece
(sea stars for
example).
Asexual Reproduction

regeneration
Asexual Reproduction

Advantage- no need to find a mate!

Disadvantage- offspring are exact
copies of their parents, so organisms
don’t change much over generations.
Doesn’t allow for adaptations and
natural selection.
Meiosis:Terms you need to know 
• Zygote: The fusion of sperm and egg.
• Gamete: A mature male (sperm) or female (egg)
germ cell that is able to unite with another of the
opposite sex to form a zygote.
• Homologous Chromosomes: are chromosome pairs,
one from each parent, that are similar in length, gene
position and centromere location.
Meiosis
• Meiosis is a special type of cell division that produces
gametes with half as many chromosomes.
• In sexual reproduction, two parents provide an
offspring with an unique gene combination. Each
parent gives 1/2 of his/her genes (Chromosomes) to
the offspring.
Video Clip
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9.swf::Stages%20of%20Meiosis
Prophase 1
• Homologous chromosomes pair up and form tetrad
Metaphase 1
• tetrads of homologous chromosomes become
attached to the spindle fibers and move to equator
Anaphase 1
• Microtubules of the
spindle fiber shorten
and pull the
chromosomes toward
the poles, taking both
sister chromatids with
them.
Telophase 1
• The nuclear membrane
reforms around the
daughter nuclei. Each
daughter nucleus
contains two sister
chromatids for each
chromosome, attached
to a common
centromere.
Prophase 2
• Nuclear envelope breaks down and a new spindle
forms.
Metaphase 2
• Spindle fibers bind to both sides of the centromere.
Anaphase 2
• Spindle fibers
contract and the
sister chromatids
move toward the
opposite side.
Telophase 2
• Nuclear envelope
reforms around the set
of daughter
chromosomes.
Four daughter cells are created with
the perfect amount of DNA.