Here are the key points about meiosis:
1. Mitosis produces genetically identical diploid body cells.
2. Meiosis produces genetically unique haploid gametes (sperm and egg cells) with half the number of chromosomes as body cells.
3. Humans have 23 chromosomes in their haploid gametes.
4. Meiosis involves two cell divisions (Meiosis I and Meiosis II) which results in four haploid daughter cells from one original diploid cell.
5. Chromosomes are replicated once before meiosis, not between the two meiotic divisions.
6. Cells become genetically different during meiosis due to independent assortment of homologous chromosomes and crossing over.
The study of the cell cycle focuses on mechanisms that regulate the timing and frequency of DNA duplication and cell division. As a biological concept, the cell cycle is defined as the period between successive divisions of a cell. During this period, the contents of the cell must be accurately replicated.
The cell cycle is regulated by cyclins and cyclin-dependent kinases.
How long is one cell cycle?
Depends. Eg. Skin cells every 24 hours. Some bacteria every 2 hours. Some cells every 3 months. Cancer cells very short. Nerve cells never.
Programmed cell death:
Each cell type will only do so many cell cycles then die. (Apoptosis)
4. Cell division - Anatomy - BSc Nursing 1st Semester - by M. Thirumurugan.pptxthiru murugan
It is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle.
It is an essential biological process in many organisms. It is the means used by multicellular organisms in order to grow, repair, and reproduce.
Types of Cell division:
Mitosis
Meiosis
Mitosis: Mitosis is a division of the nucleus to produce two new daughter cells containing chromosomes identical to the parent cell.
Phases of Mitosis:
Mitosis is a continuous process and divided into different phases based on the appearance and behavior of the chromosomes.
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
1.Prophase:
Early prophase:
During prophase chromatin (the complex of DNA and proteins contained in the nucleus), condense and become visible in a light microscope
Nucleolus disappears & Paired centrioles move to opposite ends of the cell.
The replicated chromosomes have an X shape and are called sister chromatids. The sister chromatids are joined at a point called the centromere.
Late prophase:
Nuclear membrane disappears
a structure called the mitotic spindle begins to form at opposite ends of the cell (responsible for separating the sister chromatids into two cells)
2. Prometaphase: Prometaphase is the second stage of mitosis. In prometaphase,
Chromosomes continue to condense
Kinetochores appear at the centromeres
Mitotic spindle attach to kinetochores
Centrosomes move toward opposite poles
3. Metaphase:
Metaphase is the third step in mitosis.
Mitotic spindle is fully developed
Sister chromatids line up at the spindle equator
At the end of metaphase, the centromeres start to divide
4.Anaphase:
Anaphase begin with the separation of the centromeres
Sister chromatids together break down
Sister chromatids (now called chromosomes) are pulled toward opposite poles
The sister chromatids are drawn to opposite poles of the cell by contraction of spindle fibers
5.Telophase:
Telophase begin when the two sets of daughter chromosomes have reached the two poles of the cell.
The spindle fibers breaks down,
The nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappear
The chromosomes uncoil and become less visible under the light microscope
6. Cytokinesis:
Cytokinesis is the sixth and final step of mitosis & A cleavage furrow separates the daughter cells
Cytokinesis is the process of cytoplasmic division to form two daughter cells.
Cytokinesis takes place when the Cytoplasm divides and two cells with identical genetic material are formed Daughter Cells
Meiosis:
Meiosis Takes place in the Gametes of an organism
People have a Chromosome count of 46
When an egg joins a sperm the count must stay at 46 to remain human
So, the egg can only have 23 chromosomes, and the sperm can only have 23 chromosomes
But, the integrity of the organism must be maintained.
During Meiosis diploid cells are reduced to haploid cells
Diploid (2n) to Haploid (n):
During Meiosis gamete (sex
Cell Biology (Reproduction in Cell))
Best notes for Botany/Zoology/Chemistry/Molecular Biology/Biotechnology and Biochemistry Students
Genetics
UCMS Khanewal
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The study of the cell cycle focuses on mechanisms that regulate the timing and frequency of DNA duplication and cell division. As a biological concept, the cell cycle is defined as the period between successive divisions of a cell. During this period, the contents of the cell must be accurately replicated.
The cell cycle is regulated by cyclins and cyclin-dependent kinases.
How long is one cell cycle?
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4. Cell division - Anatomy - BSc Nursing 1st Semester - by M. Thirumurugan.pptxthiru murugan
It is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle.
It is an essential biological process in many organisms. It is the means used by multicellular organisms in order to grow, repair, and reproduce.
Types of Cell division:
Mitosis
Meiosis
Mitosis: Mitosis is a division of the nucleus to produce two new daughter cells containing chromosomes identical to the parent cell.
Phases of Mitosis:
Mitosis is a continuous process and divided into different phases based on the appearance and behavior of the chromosomes.
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
1.Prophase:
Early prophase:
During prophase chromatin (the complex of DNA and proteins contained in the nucleus), condense and become visible in a light microscope
Nucleolus disappears & Paired centrioles move to opposite ends of the cell.
The replicated chromosomes have an X shape and are called sister chromatids. The sister chromatids are joined at a point called the centromere.
Late prophase:
Nuclear membrane disappears
a structure called the mitotic spindle begins to form at opposite ends of the cell (responsible for separating the sister chromatids into two cells)
2. Prometaphase: Prometaphase is the second stage of mitosis. In prometaphase,
Chromosomes continue to condense
Kinetochores appear at the centromeres
Mitotic spindle attach to kinetochores
Centrosomes move toward opposite poles
3. Metaphase:
Metaphase is the third step in mitosis.
Mitotic spindle is fully developed
Sister chromatids line up at the spindle equator
At the end of metaphase, the centromeres start to divide
4.Anaphase:
Anaphase begin with the separation of the centromeres
Sister chromatids together break down
Sister chromatids (now called chromosomes) are pulled toward opposite poles
The sister chromatids are drawn to opposite poles of the cell by contraction of spindle fibers
5.Telophase:
Telophase begin when the two sets of daughter chromosomes have reached the two poles of the cell.
The spindle fibers breaks down,
The nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappear
The chromosomes uncoil and become less visible under the light microscope
6. Cytokinesis:
Cytokinesis is the sixth and final step of mitosis & A cleavage furrow separates the daughter cells
Cytokinesis is the process of cytoplasmic division to form two daughter cells.
Cytokinesis takes place when the Cytoplasm divides and two cells with identical genetic material are formed Daughter Cells
Meiosis:
Meiosis Takes place in the Gametes of an organism
People have a Chromosome count of 46
When an egg joins a sperm the count must stay at 46 to remain human
So, the egg can only have 23 chromosomes, and the sperm can only have 23 chromosomes
But, the integrity of the organism must be maintained.
During Meiosis diploid cells are reduced to haploid cells
Diploid (2n) to Haploid (n):
During Meiosis gamete (sex
Cell Biology (Reproduction in Cell))
Best notes for Botany/Zoology/Chemistry/Molecular Biology/Biotechnology and Biochemistry Students
Genetics
UCMS Khanewal
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3. Why Are Cells Small?
• As cells get bigger, more of its cytoplasm is
located farther from the cell membrane.
• If a cell gets too big, it would take too long to
get materials into the cell and too long to get
waste out of the cell.
• Smaller cells are more efficient!
4. Cell Division
• All cells come from other living cells.
• You (and other living things) grow because your
cells get bigger and your number of cells gets
larger.
– A single cell divides into two cells.
– Two cells divide into four, etc.
• Cells must also divide because old cells die and
need new cells to replace them!
5. The Cell Cycle
• Cell cycle – regular sequence of growth and
division that eukaryotic cells undergo.
– Prokaryotic cells undergo binary fission
• Divided into three main stages:
– Interphase – cell grows into its mature size, makes a
copy of its DNA, and prepares for division.
– Mitosis – one copy of the DNA is distributed into each
of its daughter cells
– Cytokinesis – the cytoplasm divides and organelles
are distributed into the two new cells
6. Interphase
• Interphase is made up of 3 separate parts.
– G1
– S
– G2
• Interphase is the stage that the cell is in for
most of its life!
7. Sister Chromatids & Chromosomes
Copy of chromosome from mom
or dad
Chromosome made in S phase of
Interphase
Human somatic cells (any cell other than a gamete) have 23 pairs
of chromosomes. – one from mom and one from dad. These are
called homologous chromosomes.
8. • The cell’s chromatin condenses into
chromosomes
• The chromosomes look like an “X”
– Each chromosome is made up of two identical
sister chromatids attached by a centromere
– This is “created” in S phase of interphase
10. G1 – Growth Phase
• Cell doubles in size
• Cell produces all of the structures it needs to
carry out its functions
• Think of this phase as the cell just living its
normal life.
11. S – DNA Copying
• Cell makes a copy of its DNA (replication)
• This happens because the new cell needs all of
the directions for its function and survival.
• Think of this phase as placing the DNA on a
copy machine.
12. G2 – Preparation
• Cell prepares to divide
• Cell produces structures needed for cell
division
• Think of this phase as the cell double checking
everything it needs to divide.
13. Learning Checkpoint
1. T/F: Interphase is usually divided into 3 phases: G1, S, G2.
2. The ________ is the regular sequence of growth and division that cells undergo.
3. ________ is the stage of the cell cycle where the cell grows to its mature size,
copies it DNA, and prepare to divide.
4. Cells can not get too big because:
A. there is not enough DNA to support large cells
B. diffusion is too slow to provide for large cells
C. the surface area of a cell increases too fast for the cell membrane to meet its
needs.
D. all of the above
5. DNA is replicated during:
A. interphase
B. prophase
C. metaphase
D. cytokinesis
15. Mitosis
• During mitosis, the cells’ copied genetic
material separates and the cell prepares to
split into two cells
• This allows the cell’s genetic material to pass
into the new cells
– The resulting daughter cells are genetically
identical!!
16. Where Do I Find DNA?
• Chromosomes are in the
nucleus of every cell.
• Chromosomes are made
up of DNA.
• Genes are pieces of DNA
that contain the instructions
for building a protein.
17. The Four Stages of Mitosis
• Remember PMAT!
• Prophase
• Metaphase
• Anaphase
• Telophase
19. Metaphase
• The sister chromatids are pulled to the center
of the cell
• They line up in the middle of the cell
20. Anaphase
• Spindle fibers begin to shorten
• The sister chromatids are pulled to the
opposite ends of the cell
21. Telophase
• The sister chromatids arrive at the opposite
poles of the cell and begin to unravel
• New nucleus begins to form
22. Cytokinesis
• Cytokinesis is the division of the cytoplasm
• Results in two separate daughter cells with
identical nuclei
23. Cytokinesis
In plants, a cell plate forms between the two daughter nuclei.
In animal cells, it is accomplished by using microfilaments to “pinch” the cytoplasm.
25. Mitosis Learning Checkpoint
1. Which phase do cells spend the most time?
2. What are the 3 stages of interphase?
3. What kinds of cells go through mitosis?
4. What are the 4 stages of mitosis?
5. What is the result of mitosis?
27. Meiosis - the process of cell division
that produces haploid gametes (half
the number of chromosomes:
humans: 23)
28. Discovery of Meiosis
• In 1882, British cytologist Pierre-Joseph
van Beneden found different numbers of
chromosomes in different cells
• Specifically, he observed that gametes (sperm
& egg) contain half the number of
chromosomes compared to somatic cells
(nonreproductive cells).
29. Fertilization
• Van Beneden then proposed that an egg and a
sperm fuse to produce a zygote .
• The zygote contains two copies of each
chromosome (one copy from the sperm and one
copy from the egg). These are called homologous
chromosomes.
• Fertilization is the name for the fusion of
gametes.
30. Reduction Division
• Since the sperm and the egg contain only half the
number of chromosomes, they cannot be formed
from mitosis.
• Meiosis - the process of cell division that
produces gametes with half the number of
chromosomes as somatic cells
– Cell undergoes 2 rounds of cell division:
• Meiosis 1
• Meiosis 2
• Humans have 46 chromosomes in their somatic
cells.
32. Unique Features of Meiosis
Feature #1 – Synapsis
Following chromosome replication, the
homologous chromosomes pair all along their
length. This process is called synapsis.
33. Unique Features of Meiosis
Feature #2 – Crossing Over
While the homologous chromosomes are joined,
crossing over occurs. Crossing over is the
exchange of genetic material from
homologous chromosomes.
This causes genetic variations.
35. Unique Features of Meiosis
Feature #3 – Reduction Division
The chromosomes are not copied in between
the two divisions. At the end of meiosis, each
cell contains one half the genetic material.
(haploid or “n”)
37. Meiosis I
• Preceded by Interphase- chromosomes are
replicated to form sister chromatids
• Sister chromatids are genetically identical and
joined at centromere
• Single centrosome replicates, forming 2
centrosomes
38.
39. Prophase I
• Individual chromosomes first become visible
– homologous chromosomes become closely associated in
synapsis
– crossing over occurs
• Crossing over is a complex series of events in which
DNA segments are exchanged between nonsister or
sister chromatids.
40. Metaphase I
• The homologous chromosomes line up in the
center of the cell and are still held together
41. Anaphase I
• Spindle fibers shorten
• The homologous chromosomes are separated
(the sister chromatids are still paired)
• Independent assortment – random
chromosomes move to each pole; some may be
maternal and some may be paternal
42. Telophase I
• The nuclear membrane reforms around each
daughter nucleus
• Each new cell now contains two sister
chromatids that are NOT identical due to
crossing over
43. At the end of Meiosis I…
• You have made 2 cells
• Each cell contains a haploid number of chromosomes – 1 copy
of each chromosome
(for humans, each haploid cell has 23 chromosomes)
• No DNA replication occurs between Meiosis I and Meiosis I
• Meiosis II resembles normal, mitotic division
48. At the end of Meiosis II…
• At the end of Meiosis II, there are 4 haploid
cells. (only 1 copy of each chromosome)
– (for humans, each haploid cell has 23
chromosomes)
• No two of these haploid cells are alike due to
crossing over.
– This is why you and your siblings are genetically
unique!
49. Meiosis Quick Check Questions:
1. What kinds of cells does mitosis produce?
2. How many chromosomes do human haploid
cells have?
3. What kinds of cells does meiosis produce?
4. How many cells are produced when one cell
goes through meiosis?
5. How many times are chromosomes replicated
during meiosis?
6. How do cells in meiosis get to be different?
7. If an organism’s somatic cells have 36
chromosomes, how many chromosomes do
their gametes have?