Overview of Cell Division Processes: Mitosis and Meiosis
Cytokinesis
•
Divides cytoplasm
•
Animal Cells
–
Microfilaments constrict/pinch the cytoplasm
•
Plant Cells
–
Cell plate forms between two daughter nuclei
–
Cell walls then form on either side of cell plate
Mitosis Review
•
Interphase
•
Prophase
•
Metaphase
•
Anaphase
•
Telophase
•
Cytokinesis
MITOSIS
Meiosis
Meiosis
”gametes”,
”gametes”,
with
half
half
the number of
chromosomes,
chromosomes,
are produced.
During Meiosis diploid cells are reduced to haploid cells
Diploid (2n)
Diploid (2n)
Haploid (n)
Haploid (n)
If Meiosis did not occur the chromosome number in
If Meiosis did not occur the chromosome number in
each new generation would double…. The
each new generation would double…. The
offspring would die.
offspring would die.
MEIOSIS
Interphase
Meiosis I
Meiosis II
Metaphase I
Prophase I
Anaphase I
Telophase I
Telophase II
Prophase II
Metaphase II
Anaphase II
2n
2n
2n
4n
n
n
n
n
Interphase/
DNA
replicates
Meiosis I
Meiosis II
Prophase I
Prophase I
-
-
Synapsis
Synapsis
Homologous Chromosomes
Homologous Chromosomes
(
(
because a homologous pair consists of 4 chromatids it is called a “Tetrad”)
because a homologous pair consists of 4 chromatids it is called a “Tetrad”)
Meiosis I
•
Interphase –replication
•
Prophase I - homologous chromosomes pair
–
Crossing over! -
creates variation (diversity)
creates variation (diversity)
n
o
n
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Meiosis I
•
Metaphase I
–
Homologous pair line up at center (tetrad)
–
INDEPENDENT ASSORTMENT OCCURS:
INDEPENDENT ASSORTMENT OCCURS:
1. Orientation of homologous pair is random
2. **Variation**
produces 2
produces 2
n
n
distinct gametes, where n = the number of unique
distinct gametes, where n = the number of unique
chromosomes.
chromosomes.
In humans, n = 23 and 2
In humans, n = 23 and 2
23
23
= 6,000,000
= 6,000,000
Meiosis I
•
Anaphase I
–
Homologous pairs move to opposite sides of cell
•
Telophase I/Cytokinesis
–
Cell divides
Quick Questions
1.
How many cells are at the end of Meiosis 1?
2.
How many chromosomes are in each cell at
the end of meiosis 1?
2n
2n
2n
4n
n
n
n
n
Interphase/
DNA
replicates
Meiosis I
Meiosis II
Meiosis II
•
Prophase II - no DNA replication!!!
•
Metaphase II
•
Anaphase II
•
Telophase II/Cytokinesis
Quick Questions
1.
How many cells are at the end of Meiosis 2?
2.
How many chromosomes are in each cell at
the end of meiosis 2?
How many cells are at the end of meiosis?
How many chromosomes are in each cell?
Mitosis vs. Meiosis
1. Number of Cells
–
Mitosis creates 2 identical cells
–
Meiosis creates 4 individual cells
2. Number of chromosomes
–
Mitosis creates cells with 46 chromosomes (2n – diploid)
–
Meiosis creates cells with 23 chromosomes (n – haploid)
3. Locations
–
Mitosis – somatic (“normal”) cells
–
Meiosis – gametes (sex) cells
•
The Key Difference Between Mitosis and
The Key Difference Between Mitosis and
Meiosis is the Way Chromosomes Uniquely
Meiosis is the Way Chromosomes Uniquely
Pair and Align in Meiosis
Pair and Align in Meiosis
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Importance of Meiosis
•
Genetic Variation
•
Random distribution of
chromosomes
•
Chromosomes are passed
to offspring independently
of each other
A Sweet Animation!!!!!!!!!!!!!!!!!!
http://wps.prenhall.com/esm_freeman_biosci_1/7/1948/498784.cw/index.html
Fertilization
Fertilization
•
The fusion of a
sperm
sperm
and
egg
egg
to form a
zygote
zygote
.
•
A zygote is a fertilized egg
Asexual reproduction
•
Asexual reproduction
involves a single parent.
•
genetically identical offspring
•
All prokaryotes and some eukaryotes
•
can be very rapid
–
allows them to crowd out other organisms that
reproduce more slowly
Three types of asexual
Binary fission -
a parent cell splits into two identical daughter cells (E. Coli)
Fragmentation
- a parent organism breaks into pieces and each piece develops
into a new organism (Starfish – sailors thought they were killing them… not so
much
)
Budding
- a parent cell forms a bubble-like bud. The bud stays attached to the
parent cell while it grows and develops. When the bud is fully developed, it breaks
away from the parent cell and forms a new organism.
-
JELLYFISH don’t rely solely on budding to reproduce – 1
st
release a sperm & egg
into the H20. Zygote grows into a basic organism called a polyp, which lives
attached to the base of a rock. The polyp then grows, before releasing a
genetically identical bud of itself, that grows into an adult jellyfish.
Sexual Reproduction
•
involves two parents
•
parents produce
gametes
•
Gametes are
haploid
cells
•
two gametes unite is called
fertilization
•
The fertilized cell is a
zygote
.
•
A zygote is
diploid
cell
Sexual vs. Asexual Reproduction
Asexual
•
Organisms inherit all
chromosomes from single
parent
–
Genetically identical
•
Little energy
•
No mate needed
•
Good for stable env’t
•
Bacteria
Sexual
•
Chromosomes from 2
parents
•
Genetic variation
–
Good for changing env’t
•
Most animals/organisms
Why reproduce sexually?
Greater chance of beneficial mutations
•
Crossing over, random assortment
Check the correct box for each description
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase/Cytokinesis I
1.
Prophase II
Cells from Meiosis I
2. Metaphase II
3. Anaphase II
4. Telophase II
/Cytokinesis II
Cell division involves two main processes: mitosis and meiosis. Mitosis is responsible for the division of somatic cells, producing identical daughter cells. It consists of prophase, metaphase, anaphase, and telophase, followed by cytokinesis. In contrast, meiosis is crucial for the formation of gametes with half the chromosome number, allowing for genetic diversity. Meiosis involves two rounds of division (Meiosis I and Meiosis II) and includes processes like synapsis, crossing over, and independent assortment, leading to the generation of genetically distinct gametes.
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Presentation Transcript
Cytokinesis Divides cytoplasm Animal Cells Microfilaments constrict/pinch the cytoplasm Plant Cells Cell plate forms between two daughter nuclei Cell walls then form on either side of cell plate
Mitosis Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis MITOSIS
Meiosis gametes , withhalfthe number ofchromosomes, are produced. During Meiosis diploid cells are reduced to haploid cells Diploid (2n) Haploid (n) If Meiosis did not occur the chromosome number in each new generation would double . The offspring would die.
MEIOSIS Interphase Prophase I Metaphase I Anaphase I Telophase I Meiosis I Prophase II Metaphase II Anaphase II Meiosis II Telophase II
2n 2n 4n Meiosis I Interphase/ DNA replicates 2n Meiosis II n n n n
Prophase I - Synapsis Homologous chromosomes sister chromatids sister chromatids Tetrad
Homologous Chromosomes (because a homologous pair consists of 4 chromatids it is called a Tetrad ) eye color locus eye color locus hair color locus hair color locus Paternal Maternal
Meiosis I Interphase replication Prophase I - homologous chromosomes pair Crossing over! - creates variation (diversity) nonsister chromatids Tetrad chiasmata: site of crossing over
Meiosis I Metaphase I Homologous pair line up at center (tetrad) INDEPENDENT ASSORTMENT OCCURS: 1. Orientation of homologous pair is random 2. **Variation** produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223 = 6,000,000
Meiosis I Anaphase I Homologous pairs move to opposite sides of cell Telophase I/Cytokinesis Cell divides
Quick Questions 1. How many cells are at the end of Meiosis 1? 2. How many chromosomes are in each cell at the end of meiosis 1?
2n 2n 4n Meiosis I Interphase/ DNA replicates 2n Meiosis II n n n n
Meiosis II Prophase II - no DNA replication!!! Metaphase II Anaphase II Telophase II/Cytokinesis
Quick Questions 1. How many cells are at the end of Meiosis 2? 2. How many chromosomes are in each cell at the end of meiosis 2?
How many cells are at the end of meiosis? How many chromosomes are in each cell?
Meiosis Mitosis Two cell divisions Half the original chromosomes Homologous Chromosomes pair up Cytokinesis Four daughter cells 46 Chromosomes at end
Mitosis vs. Meiosis 1. Number of Cells Mitosis creates 2 identical cells Meiosis creates 4 individual cells 2. Number of chromosomes Mitosis creates cells with 46 chromosomes (2n diploid) Meiosis creates cells with 23 chromosomes (n haploid) 3. Locations Mitosis somatic ( normal ) cells Meiosis gametes (sex) cells
The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis
Whiteboard Questions 1. If a cell has 40 chromosomes, how many are in each cell at the end of meiosis 1? 2. Meiosis 2? 3. Mitosis? 4. T/F: Mitosis creates 2 different cells 5. T/F: A difference between meiosis & mitosis is that meiosis occurs in gametes and mitosis occurs in somatic cells.
Meiosis Mitosis Chromosome Number: Reduced by half (haploid) Remains the same (diploid) Pairing of Homologues: Yes No Cellular (asexual) Reproduction; general growth and repair of the body Function: sexual reproduction #of Divisions: 2 1 #of Cells produced: 4 2 Creates: Sex cells (Gametes) Somatic Cells Crossing Over: Yes No Genetically: different identical
Importance of Meiosis Genetic Variation Random distribution of chromosomes Chromosomes are passed to offspring independently of each other
A Sweet Animation!!!!!!!!!!!!!!!!!! http://wps.prenhall.com/esm_freeman_biosci_1/7/1948/498784.cw/index.html
Fertilization The fusion of a sperm and egg to form a zygote. A zygote is a fertilized egg sperm n=23 n=23 egg 2n=46 zygote
Asexual reproduction Asexual reproduction involves a single parent. genetically identical offspring All prokaryotes and some eukaryotes can be very rapid allows them to crowd out other organisms that reproduce more slowly
Three types of asexual Binary fission - a parent cell splits into two identical daughter cells (E. Coli) Fragmentation - a parent organism breaks into pieces and each piece develops into a new organism (Starfish sailors thought they were killing them not so much ) Budding - a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops. When the bud is fully developed, it breaks away from the parent cell and forms a new organism. - JELLYFISH don t rely solely on budding to reproduce 1st release a sperm & egg into the H20. Zygote grows into a basic organism called a polyp, which lives attached to the base of a rock. The polyp then grows, before releasing a genetically identical bud of itself, that grows into an adult jellyfish.
Sexual Reproduction involves two parents parents produce gametes Gametes are haploid cells two gametes unite is called fertilization The fertilized cell is a zygote . A zygote is diploid cell
Sexual vs. Asexual Reproduction Asexual Organisms inherit all chromosomes from single parent Genetically identical Little energy No mate needed Good for stable env t Bacteria Sexual Chromosomes from 2 parents Genetic variation Good for changing env t Most animals/organisms Why reproduce sexually? Greater chance of beneficial mutations Crossing over, random assortment
Check the correct box for each description Meiosis Mitosis 1. Two cell divisions 2. Occurs in gametes 3. Half the original chromosomes 4. Homologous Chromosomes pair up 5. Creates identical cells 6. Four daughter cells 7. Same #of chromosomes at end
2. Metaphase I 1. Prophase I 3. Anaphase I 4. Telophase/Cytokinesis I
3. Anaphase II 1. Prophase II Cells from Meiosis I 2. Metaphase II 4. Telophase II /Cytokinesis II
