Why does
reproduction require
2 types of cell
division?
Asexual & Sexual
Reproduction
• NOVA-How Cells Divide
– http://www.pbs.org/wgbh/nova/body/howcells-divide.html
• NOVA- Cancer
– http://www.pbs.org/wgbh/nova/body/howcancer-grows.html
• Cancer Video (50min)
– http://video.pbs.org/video/1872446235/
• Cancer Video (12 min youtube)
– https://www.youtube.com/watch?v=46Xh7O
FkkCE
• Meiosis
– https://www.youtube.com/watch?v=rqPMp0
Asexual reproduction & cell division
• Asexual reproduction
is reproduction
involving only one
source of genetic
material (i.e. one
parent).
• This means that
offspring are genetically
identical to the parent,
or clones.
Several types of asexual
reproduction:
• Binary fission occurs
when a unicellular
organism (such as
bacteria or an amoeba)
divides into two equally
sized cells for the
purpose of
reproduction.
Several types of asexual
reproduction:
• Budding occurs when
simple organisms (such
as yeast or hydra)
produce much smaller
cells than those of the
parent organism.
Several types of asexual
reproduction:
• Sporulation occurs
when an organism (such
as mushrooms) produce
spores - tiny packets of
DNA - for the purpose of
reproduction.
Several types of asexual reproduction:
• Vegetative
propagation occurs
when a portion of a
plant goes through cell
division in order to
produce another plant.
Several types of asexual reproduction:
• Regeneration occurs
when a part of an
animal (such as an
earthworm) undergoes
cell division to produce
a new organism.
Fill It In …
Simple pictures of asexual
reproduction:
Binary fission
Budding
Sporulation
Vegetative propagation
Regeneration
Advantages & Disadvantages of
Asexual Reproduction
• Advantages
– Advantages of asexual
reproduction include
speed of reproduction
and producing multiple
copies of successful
genetic combinations.
Advantages & Disadvantages of
Asexual Reproduction
• Disadvantages
– Disadvantages of asexual
reproduction include
increased risk of a single
factor affecting an entire
population due to lack of
genetic variation
• Mitosis is usually the
mechanism that allows
asexual reproduction to
occur.
• For example, when an
earthworm is cut in half,
cells must use mitosis to
divide in order to
produce cells which will
reconstruct the missing
portion
Sexual reproduction & cell division
• Sexual reproduction is
reproduction involving
two sources of genetic
material (i.e. two
parents).
• This means that offspring
will be genetic
combinations of the two
parents.
Sexual reproduction & cell division
• Gametes are sex cells,
such as sperm and egg
• The purpose of a
gamete is to fuse with
another gamete to
combine genetic
material (fertilization).
Sexual reproduction & cell division
• A zygote is the cell
which is produced by
fertilization.
• The zygote will develop
into an embryo.
Fill It In …
Picture of fertilization:
Advantages & Disadvantages of
Sexual Reproduction
• Advantages
– The main advantage of
sexual reproduction is
genetic variation.
– With many genetic
possibilities, the likelihood
of a successful combination
of traits for a particular
environment is high
Advantages & Disadvantages of
Sexual Reproduction
• Disadvantages
– The disadvantages of sexual
reproduction include the
necessity of mating for
fertilization (which requires
more time) and the risks of
unfavorable genetic
combinations.
Fill It In …
Summary:
Advantage Disadvantage
Asexual
Sexual
• Although sexual reproduction begins differently
than asexual reproduction (with two parents as
opposed to one parent), sexual reproduction
also relies on cell division
Crossing Over- MYP
Segregation of Alleles- MYP
Meiosis
• Meiosis is a type of cell
division which produces
gametes.
• Meiosis is a unique type of
cell division because it
divides the genetic
material in half, allowing
for fertilization.
• Example: Human body
cells contain 46
chromosomes
• In order for a zygote
(fertilized egg) to
contain 46
chromosomes, the
sperm and egg must
each contain only 23
chromosomes
Meiosis
• Mitosis is the process which
allows the zygote to begin
dividing to produce a
multicellular organism.
• The cells must also
differentiate (become
different types of cells to
carry out different
functions)
Fill It In …
In sexual reproduction …
Job of meiosis Job of mitosis -
Check Yourself!
1. How many sources of genetic material are
involved in asexual reproduction? In sexual
reproduction?
2. Name five types of asexual reproduction.
3. Why is mitosis necessary for asexual
reproduction?
4. Name one advantage and one disadvantage of
asexual reproduction.
5. What are gametes? How is a zygote produced
from gametes?
6. Name one advantage and one disadvantage of
sexual reproduction.
7. How are both mitosis and meiosis necessary for
sexual reproduction?
Check Yourself!
1. How many sources of genetic material are
involved in asexual reproduction? In sexual
reproduction?
ASEXUAL - ONE SOURCE/ONE PARENT
SEXUAL - TWO SOURCES/TWO PARENTS
Check Yourself!
2. Name five types of asexual reproduction.
BINARY FISSION
BUDDING
SPORULATION
VEGETATIVE PROPAGATION
REGENERATION
Check Yourself!
3. Why is mitosis necessary for asexual
reproduction?
TO PRODUCE GENETICALLY IDENTICAL
DAUGHTER CELLS
Check Yourself!
4. Name one advantage and one disadvantage of
asexual reproduction.
ADVANTAGE - SPEED
MULTIPLE COPIES
DISADVANTAGE - NO GENETIC VARIATION
Check Yourself!
5. What are gametes? How is a zygote produced
from gametes?
GAMETES ARE SEX CELLS (SPERM OR EGG)
ZYGOTES ARE PRODUCED BY THE
FERTILIZATION OF GAMETES
Check Yourself!
6. Name one advantage and one disadvantage of
sexual reproduction.
ADVANTAGE - GENETIC VARIATION
DISADVANTAGE - TAKES TIME
RISK OF UNFAVORABLE
GENETIC COMBINATIONS
Check Yourself!
7. How are both mitosis and meiosis necessary for
sexual reproduction?
MEIOSIS - CREATES GAMETES; CUTS
CHROMOSOME NUMBER IN HALF
MITOSIS - GROWTH OF A MULTICELLULAR
ORGANISM
How does meiosis
produce gametes?
• Recall that a gamete is
very different from a
somatic (body) cell.
Somatic cells & gametes
• A somatic cell is diploid,
which means that it
contains two of each
type of chromosome.
•
Somatic cells &
gametes
These chromosome pairs are
called homologous
chromosomes.
• For example, a human has 23
types of chromosomes.
• A human somatic cell has 46
total chromosomes, consisting
of 23 homologous pairs.
Somatic cells & gametes
• A gamete is haploid, which
means it contains only one of
each type of chromosome (one
from each homologous pair).
• For example, a human egg cell
(ovum) contains 23 total
chromosomes.
Diploid vs Haploid
Diploid vs Haploid
Fill It In …
# of chromosomes in a human …
DIPLOID cell ______
HAPLOID cell ______
Meiosis
Eukaryotic Cell Cycle & Meiosis
• At the end of interphase
(the longest part of the
cell cycle in which the cell
completes normal life
functions), the cell
duplicates the DNA.
• This creates doubled
chromosomes.
• The cell is now ready to
divide.
Meiosis requires 2 cell divisions:
• Meiosis I is called the
reduction division.
• In this division, the
homologous pairs of doubled
chromosomes are separated.
• The end result of Meiosis I is
two daughter cells, each of
which is haploid but contains
doubled genetic material
Meiosis requires 2 cell divisions:
• Meiosis II uses the same basic
steps as mitosis.
• In this division, the doubled
chromosomes are separated.
• The end result of Meiosis II is
four daughter cells, each of
which is haploid and contains
no duplicated DNA.
Graphical representation of Meiosis:
Meiosis I
46
doubled
23
doubled
23
doubled
Meiosis II
23
singled
23
singled
23
singled
23
singled
Fill It In …
Meiosis I
46
doubled
23
doubled
Label each of
the cells in the
diagram as
“diploid” or
“haploid”
23
doubled
Meiosis II
23
singled
23
singled
23
singled
23
singled
Meiosis provides several sources of
genetic variation:
• Gene mutations can
occur during the
duplication of DNA at the
end of interphase before
meiosis (or mitosis)
begins.
Meiosis provides several sources of
genetic variation:
• Crossing over occurs
when the homologous
pairs come together
during Meiosis I (Prophase
I).
• In crossing-over, a part of
one chromosome can
switch places with the
same part of the
homologous chromosome.
Meiosis provides several sources of
genetic variation:
• Then, when the
homologous pairs are
separated, each
chromosome will be
different than the original.
Meiosis provides several sources of
genetic variation:
• Random assortment of
chromosomes into
daughter cells during
Meiosis I allows for a
mix of the chromosomes
inherited from each
parent.
Meiosis provides several sources of
genetic variation:
• Nondisjunction, when
homologous
chromosomes do not
properly separate, may
occur during Meiosis I or
II, creating a gamete
with one too many or
one too few
chromosomes.
Meiosis provides several sources of
genetic variation:
• The random
fertilization of any one
egg by any one sperm
allows for numerous
genetic combinations in
offspring.
Warm- Up
Mitosis
1. Number of cells at the
beginning and the end?
2. Number of divisions?
3. Haploid or diploid at the
end?
4. Number of
Chromosomes at the
beginning and the end
5. Are daughter cells
identical to the parent
cells?
6. Advantages of this type
of division
Meiosis
1. Number of cells at the
beginning and the end?
2. Number of divisions?
3. Haploid or diploid at the
end?
4. Number of
Chromosomes at the
beginning and the end
5. Are daughter cells
identical to the parent
cells?
6. Advantages of this type
of division
Fill It In …
Summary of sources of genetic
variation:
1.
2.
3.
4.
5.
Check Yourself!
1. How is the chromosome number of a gamete
different from the chromosome number of a
somatic cell?
2. What types of cells are diploid? Haploid?
3. What is the purpose of meiosis?
4. What is another name for Meiosis I?
5. How is the purpose of Meiosis I different from the
purpose of Meiosis II?
6. Name five sources of variation Meiosis provides.
7. Describe crossing-over.
Check Yourself!
1. How is the chromosome number of a gamete
different from the chromosome number of a
somatic cell?
GAMETES HAVE 1/2 THE NUMBER OF
CHROMOSOMES
Check Yourself!
2. What types of cells are diploid? Haploid?
DIPLOID = SOMATIC OR BODY CELLS
HAPLOID = GAMETES OR SEX CELLS
Check Yourself!
3. What is the purpose of meiosis?
TO CREATE HAPLOID CELLS (CELLS WITH 1/2
THE “NORMAL” CHROMOSOME NUMBER)
Check Yourself!
4. What is another name for Meiosis I?
REDUCTION DIVISION
Check Yourself!
5. How is the purpose of Meiosis I different from the
purpose of Meiosis II?
MEIOSIS I CREATES HAPLOID DOUBLED
CHROMOSOMES
MEIOSIS II CREATES HAPLOID SINGLE
CHROMOSOMES
Check Yourself!
6. Name five sources of variation Meiosis provides.
GENE MUTATIONS
CROSSING OVER
RANDOM ASSORTMENT
NONDISJUNCTION
RANDOM FERTILIZATION
Check Yourself!
7. Describe crossing-over.
CROSSING-OVER OCCURS WHEN
HOMOLOGOUS PAIRS COME TOGETHER
(OVERLAP) DURING PROPHASE I.
PART OF ONE CHROMOSOME SWITCHES
PLACES WITH THE SAME PART OF THE
HOMOLOGOUS CHROMOSOME.
THIS RESULTS IN A NEW COMBINATION OF
GENETIC MATERIAL.