CELL BIOLOGY AND GENETICS
ASSIGNMENT
STAGES OF MITOSIS AND MEIOSIS
Presented by : Anshika Rathaur
Roll number : UE231011
Submitted by : Meenakshi Ma’am
Date : 01/08/2024
Content of DNA becomes double
Karyokinesis
Cytokinesis
CELL CYCLE
INTERPHASE (95%)
The cell grows and copies its DNA
- Preparatory phase
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G1 : Cell Growth
S : DNA synthesis
G2 : More growth,
preparation for
mitosis
MITOSIS PHASE(5%)
The cell divides its DNA and cytoplasm,
and forming its new cell.
- Actual division
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PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
INTERPHASES OF THE CELL CYCLE
• G0 phase - The G0 phase, also known as the resting phase, is the time when the cell is neither
dividing nor preparing to divide. During this time, the cell is performing maintenance and its other
functions.
• G1 phase (Gap 1) - G1 phase is the phase of the cell between mitosis and initiation of replication of
the genetic material of the cell. During this phase, the cell is metabolically active and continues to
grow without replicating its DNA.
• S phase (Synthesis) - DNA replication takes place during this phase. If the initial quantity of DNA in
the cell is denoted as 2N, then after replication it becomes 4N. However the number of chromosomes
does not vary, viz., if the number of chromosomes during G1 phase was 2n, it will remain 2n at the
end of S phase. The centriole also divides into two centriole pairs in the cells which contain centriole.
• G2 phase (Gap 2) -During this phase, the RNA, proteins, other macromolecules required for
multiplication of cell organelles, spindle formation, and cell growth are produced as the cell prepares
to go into the mitotic phase.
MITOSIS VS MEIOSIS
Mitosis : A specific stage in the cell cycle where somatic cells divide, resulting in two identical diploid daughter cells.
Meiosis : The process by which sex cells divide, resulting in four haploid gametes.
(Diploid means a cell has two copies of each chromosomes. And haploid means a cell has one copy of each
chromosome.)
Mitosis
Meiosis
▪ A type of cell division
▪ Occurs in somatic cells
▪ Occurs in four phases:
prophase metaphase anaphase telophase
▪ Results in two genetically identical daughter
cells
▪ Resulting daughter cells are diploid
▪ Chromosome number remains the same
▪ Also a type of cell division
▪ Occurs in sex cells (egg & sperm)
▪ Occurs in eight phases total (same phases
as mitosis but repeated)
▪ Results in four genetically unique daughter
cells
▪ Resulting daughter cells are haploid
▪ Chromosome number is halved in each
daughter cell
Now we will discuss about Meiosis
Meiosis
Meiosis I
meiosis ii
Reductional division
(content of DNA reduced)
Equational division
(content of DNA remains same
Prophase I
Liptotene
Zygotene
Pachytene
Diplotene
Diakynesis
Most of the events that function to differentiate meiosis from
mitosis occur in Prophase I
Homologous chromosomes form bivalents (or tetrads) and crossing
over occurs between non-sister chromatids
Prophase I is divided into 5 distinctive sub-stages:
1) Leptotene – The chromosomes begin to condense and are attached to the nuclear
membrane via their telomeres
2) Zygotene – Synapsis begins with a synaptonemal complex forming between
homologous chromosomes
3) Pachytene – Crossing over of genetic material occurs between non-sister chromatids
4) Diplotene – Synapsis ends with disappearance of synaptonemal complex; homologous
pairs remain attached at chiasmata
5) Diakinesis – Chromosomes become fully condensed and nuclear membrane
disintegrates prior to metaphase I
Some basic terms ➢ Homologous chromosomes – Homologous chromosomes are those with the same pair of chromosomes. Homologous
chromosomes are similar but not identical. Each carries the same genes in the same order but the alleles for each trait may not
be the same.
➢ Non-homologous chromosomes – Non-homologous chromosomes are those with separate pairings of chromosomes.
These are the chromosomes that contain alleles for the different types of genes.
➢ Bivalent – A bivalent is one pair of chromosomes (homologous chromosomes) in a tetrad. It is usually is used to describe
homologous chromosomes that are in synapsis during meiosis.
➢ Tetrad – A tetrad is the association of a pair of homologous chromosomes (4 sister chromatids) physically held together by at
least one DNA crossover.
➢ Crossing over - Crossing over, as related to genetics and genomics, refers to the exchange of DNA between paired homologous
chromosomes (one from each parent) that occurs during the development of egg and sperm cells (meiosis).
➢ Chiasmata – It is the point of crossing over or site where the exchange of genetic material takes place between two homologous,
non-sister chromatids.
➢ Synaptonemal complex – It is a protein lattice that resembles railroad tracks and connects paired homologous chromosomes in
most meiotic systems.
Amitosis (Direct Cell Division): In this process, the nucleus of a cell
lengthens and a constriction appears. The nucleus becomes dumb-bell
shaped and then divides into two. Thus, they do not necessarily pass
through any phase. This type of division mainly takes place in unicellular
organisms.
Let's practice some questions....
Question 1 : If we have a somatic cell which
have 46 chromosomes then how many
chromosomes will the sperm produced in his
body?
Answer 1 : 23 chromosomes
(Because somatic cell is diploid (2n) and
sperm cell is haploid (n) so in sperm cell,
numbers of chromosomes will become half).
Question 2 : If we have 10 bivalent then how many
chromosomes will be present in Anaphase II ?
Answer 2 : 20 chromosomes
Explanation :
10 bivalent = 20 chromosomes
( 1 bivalent = 2 chromosomes )
so when meiosis I complete we will have 10
chromosomes remain because in meiosis I,
reductional division occurs. And in Anaphase II,
sister chromatids separate so we have 20
chromosomes.
Question 3 : If we have 15 bivalent then how many
chromosomes will be present in Metaphase I ?
Answer 3 : 30 chromosomes
15 bivalent = 30 chromosomes
(as nothing change in metaphase I)
Question 4 : If we have 2C in G1 phase, then how
many DNA copy will be present in Anaphase II ?
Answer 4 : 2C
Explanation :
G1 phase = 2C (2 DNA copy)
S phase = 4C
When Meiosis I complete, we'll have 2C (2 DNA
copy) then in Anaphase II, there will be 2C.
THANK YOU