Download File

Meiosis and Sexual
Reproduction
I. Meiosis
Meiosis is a special type of cell division that produces
haploid cells.
It only occurs in the gametes (sex) forming cells of the
male and female organism.
When the gametes unite at fertilization, the original
chromosome number for that organism is restored in the
new individual.
The formation of gametes is essential to the continuation
of a species.
This special process of gamete formation from diploid cells
is called meiosis.
The cells produced in this process have half (haploid) the
number of chromosomes than the original cells.
There are 2 divisions in this process.
State Test Question
In order for humans to have a normal
number of chromosomes, sex cells
must be—
haploid.
diploid.
triploid.
tetraploid.
State Test Question
What is the primary purpose of
meiosis?
Production of haploid somatic cells
Production of diploid gametes
Production of proteins
Production of haploid gametes
State Test Question
Unlike mitosis, meiosis occurs only in—
reproductive cells.
muscle cells.
connective tissue cells.
nerve cells.
State Test Question
What structures carry the MOST
genetic information for a leaf cell?
Chromosomes
Ribosomes
Centrioles
Chloroplasts
•
Male and female meiosis processes are different in the number
of cells produced.
Crossing over and swapping of genetic information can
occur during Prophase I of this process.
Somatic Cell- Any “body” cell other than a sperm or egg cell.
Autosome- A chromosome found in a cell that is NOT a sex
determining chromosome.
Sex Chromosome- A chromosome that determines the
organism’s sex—male or female. XX= female and XY= male.
Ova/Egg- The sex cell formed in the female by meiosis.
Sperm- The sex cell formed in the male by meiosis.
Fertilization- Union of egg and sperm to form a new individual
organism.
Zygote- A fertilized cell. A diploid cell that results from the union
of egg and sperm.
Sex Chromosomes
Somatic Cell
(Liver Cell)
Zygote
Egg, Sperm, Fertilization
Meiosis is known as the cell division in which 1 diploid (2n) cell
produces 4 haploid (n) cells called sex cells or gametes, which have half
the number of chromosomes as a body cell of the parent cell.
K. During meiosis, the chromosome number is REDUCED by one half
and gametes are formed.
Meiosis occurs in the _REPRODUCTIVE_organs, the
_OVARIES_in females, and the _TESTES_in males.
E. The gametes are ova, or _EGG_, in females, and
_SPERM_in males.
F. The union of the egg and the sperm is called
_FERTILIZATION_and produces a zygote.
L. A sex cell begins meiosis with the diploid number (2n=46) of
chromosomes in humans.
The cell undergoes two divisions, but the chromosomes are duplicated only
once.
The two divisions result in 4 daughter cells, each having one half the
number of chromosomes of the parent cell (haploid number or n=23
chromosomes in humans.)
Egg (23)
+
Sperm (23)
→
Zygote (46)
Unlike body/somatic cells which contain 46 chromosomes (2n), the sex cells
each contain 23 (n) chromosomes, so when fertilization occurs, the zygote
will have 46 chromosomes.
**If a gamete contained the 2n number of chromosomes, fertilization would
result in a zygote with twice the diploid number, or 92 chromosomes and not
viable (not being able to survive).
Humans have 23 pairs of chromosomes. One pair are the sex
chromosomes.
State Test Question
Sexual reproduction in plants depends
on sex cells being produced by the
process of—
osmosis.
fermentation.
transpiration.
meiosis.
Formation Of Egg And Sperm
Oogenesis
The formation of the egg
cells in females occurs in
the ovaries
Produces 1 viable egg cell
and 3 POLAR BODIES.
Spermatogenesis
The formation of the sperm
cell in males occurs in the
testes
Produces 4 viable SPERM
cells
Oogenesis
Spermatogenesis
Meiosis Process
In meiosis a spindle forms and cytoplasm divides
in the same way as occurs in mitosis, but what
happens to the chromosomes in meiosis is very
different.
Meiosis has two divisions:
Meiosis I—Meiosis I begins with 1
diploid (2n) cell.
Meiosis II—By the end of Meiosis II,
there are four haploid (n) cells.
During Interphase that precedes Meiosis I, the cell
also replicates its chromosomes (DNA). Each
chromosome then consists of two identical sister
chromatids, held together by a centromere. So,
meiosis starts with homologous chromosomes
(homologous chromosomes are similar in size, shape,
and genetic content.)
Meiosis I:
There are four phases of Meiosis I:
Prophase I
Metaphase I
Anaphase I
Telophase I
* (on the following
slides) These are
unique steps to
meiosis. They do not occur in
mitosis
1. Prophase I
*Step 1—The chromosomes (DNA) coil up becoming visible
and a spindle forms. The nuclear membrane and nucleolus
disappear.
*Step 2— Synapsis occurs
Synapsis is the pairing of homologous chromosomes.
A tetrad is formed.
A tetrad is the pair of homologous chromosomes.
**Crossing over can occur here.
C. Crossing over
i. The exchange of genetic material.
ii. This allows for genetic variation among
organisms.
2. Metaphase I
Tetrads are moved by spindle fibers to the equator.
**They line up in homologous pairs. In mitosis, they line up
independently.
3. Anaphase I
Homologous chromosomes separate, chromosomes of sister
chromatids move to opposite poles.
**The chromatids do not split as in mitosis. Whole X’s
4. Telophase I
Chromosomes gather at the poles of the cell.
The cytoplasm divides.
**Each cell has 1 homologous pair. These chromosomes are
still attached by centromeres forming two daughter cells.
Another cell division is needed because each chromosome is
still doubled, containing two identical sister chromatids.
Meiosis II
Meiosis II is similar to mitosis in that the chromatids
separate.
There are four phases of Meiosis II:
Prophase II –A new spindle forms around the
chromosomes.
Metaphase II-chromosomes move to the equator of the cell.
Anaphase II-Sister chromatids separate and move to
opposite poles.
Telophase II-Spindle fibers
dissolve, nuclear membrane
reappears, and the
cytoplasm
divides.
At the end of Meiosis II, 4 haploid cells (n=23) have
been formed from the original diploid cell (2n=46)
Mitotic Cell
Division
Meiotic Cell
Division
State Test Question
During which phase of the process
pictured below is DNA replicated?
Prophase II
Metaphase II
Anaphase II
Telophase II and Cytokinesis II
23
+
Fertilization
Egg
Sperm
23
=
46
Zygote
23
+
23
=
46
When a sperm fertilizes an egg, the zygote
once again has the diploid number of
chromosomes. It can then develop by mitosis
into a multicellular organism.
Zygote→tissue→organ→organ systems→organism
(1 cell)
V. Comparison of meiosis to mitosis.
A. DNA replication takes place only once during
both meiosis and mitosis. However, there are two
nuclear divisions during meiosis and only one
during mitosis.
B. Four daughter cells (gametes) are produced
by meiosis. Mitosis results in two daughter cells.
C. The four gametes formed by meiosis are
haploid. The daughter cells produced by mitosis
have the same chromosomal number as the
parental cell (DIPLOID).
D. The four daughter cells from meiosis are not
genetically identical to each other or to the mother
cell. The daughter cells from mitosis are
genetically identical to each other and to the
mother cell.
State Test Question
Human cells have 46 total chromosomes in 23 pairs. Which of the
following represents the changes in chromosome number through
the stages of meiosis?
Which of the following is a characteristic of asexual reproduction?
Offspring identical to a single parent
Unique haploid gametes
Unique offspring from two parents
Crossing over during synapsis
State Test Question
Meiosis is different from mitosis
because meiosis produces—
consistent genetic makeup of all
gametes.
larger daughter cells.
two gametes for every original parent
cell.
cells with half the number of
chromosomes.
State Test Quesiton
The number of chromosomes in the egg
of a potato plant is 24. The number of
chromosomes in the cells of the
potato root is—
12
24
36
48
State Test Question
A species with 12 chromosomes in
each somatic cell will produce sex
cells with—
A. 3 chromosomes.
B. 4 chromosomes.
C. 6 chromosomes.
D. 24 chromosomes
State Test Question
What is a primary difference between mitosis
and meiosis?
Mitosis involves two cell divisions, and
meiosis involves only one.
Mitosis produces diploid cells, while
meiosis produces haploid cells.
Interphase and DNA replication occur only
in mitosis.
There is no difference between the two
processes.
State Test Question
The purpose of meiosis is—
production of haploid gametes.
asexual reproduction of unicellular
organisms.
duplication of diploid cells.
production of diploid gametes
State Test Question
The final products of meiosis are—
haploid cells.
diploid cells.
triploid cells.
polypoid cells.
II. Reproduction
There are two types of reproduction:
Sexual Reproduction
Asexual Reproduction
1. Sexual Reproduction
Two parents are involved, each contributing a sex cell, or
gamete.
The production of offspring through meiosis.
Gametes (egg & sperm – haploid cells) fuse to produce a
diploid zygote, which then develops into a new organism.
During meiosis, members of a pair of chromosomes tend
to exchange genetic material before they separate. As a
result, sex cells contain different sets of chromosomes
and genes. The union of a sperm
cell and an egg cell will produce
gene combinations that differ from
those of the parents. Sexual reproduction allows the recombination of
genetic information.
Asexual Reproduction
The production of offspring from 1 parent, without the
union of gametes.
Offspring are identical to parent (identical genetic
makeup.)
An individual produced by asexual reproduction is a clone.
A clone is an organism that is genetically identical to its
parents.
Only mitotic cell division occurs in asexual reproduction.
Methods of Asexual Reproduction in monerans (bacteria),
protests, fungi, and plants include binary fission,
budding, vegetative propogation, and spore formation.
The advantage for bacteria producing by binary (asexual
reproduction) is that it can be done so fast. Ex: E. coli
can produce “1 million” new cells in 7 hours!!! Asexual
reproduction allows organisms to produce many offspring
in a short period of time.
State Test Question
Meiosis results in greater genetic variation
than asexual reproduction because it—
is a lengthy process full of errors.
results in a greater number of offspring.
is more common in higher order species.
allows the recombination of genetic
information.
Binary fission in an amoeba
Binary fission in
Bacteria or amoeba
1st DNA is copied so
that each new cell
will have a copy of
the genetic
information.
2nd The bacterium
or amoeba is
pinched into 2
independent cells
Budding in yeast
New individuals split off from existing ones. The
bud may break from the parent and become an
independent organism
Vegetative Propagation: Plants
send out runners that allow new
plants to grow.
Alternation of Generation: Some
organisms, such as ferns, use both
sexual and asexual reproduction.
State Test Quesiton
Compared to sexual reproduction,
asexual reproduction results in a—
greater variation in offspring.
larger number of identical cells.
longer life span of a cell.
fewer number o cells dividing
State Test Question
What are two sources of genetic
variation associated with sexual
reproduction?
Binary fission and budding
Mitosis and meiosis
Crossing over and independent
assortment
Diploid gametes and DNA replication
State Test Question
Bacteria cells reproduce by binary
fission, a type of asexual cell division.
One advantage of binary fission is—
greater genetic variation in daughter
cells.
the ability to reproduce quickly.
greater resistance to disease.
the ability to live under anaerobic
conditions.
State Test Question
The primary difference between sexual and
asexual reproduction is—
asexual reproduction occurs only in
multicellular organisms.
asexual reproduction requires a
multicellualr parent and a single-celled
parent.
sexual reproduction combines DNA from
parent cells.
sexual reproduction occurs in only singlecelled organisms.
State Test Question
According to the graph, one reason that
more of the Animal A population
survived is because sexual
reproduction produces—
individual variation within a
population.
larger numbers of viable
offspring.
more female individuals than male.
different forms for each generation.
For Meiosis project:
Prophase 1: nuclear membrane
disappears, spindle fibers form,
centrioles move to opposite sides of
cell, chromatin becomes
chromosomes then crossing over
occurs
Metaphase 1: No nuclear membrane,
centrioles are on opposite sides of
cell, spindle fibers move chromosome
pairs to the center of the cell
For Meiosis project
Anaphase 1: No nuclear membrane,
centrioles are on opposite sides of
cell, spindle fibers split chromosome
pairs and move whole chromosomes
to opposite sides of the cell
Telophase 1: Nuclear membranes
reappear, centrioles are on opposite
sides of the cell, spindle fibers
disappear, chromosomes become
chromatin