Download Cell Division and Reproduction

The Continuity of Life
How Cells Reproduce
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Cell division is at the heart of the
reproduction of cells and organisms
Organisms can reproduce sexually or
asexually.
Some organisms make exact copies of
themselves, asexual reproduction.
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Other organisms make similar copies of
themselves in a more complex process, sexual
reproduction
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Cells arise only from preexisting cells
Cellular reproduction is called cell division
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Cell division allows an embryo to develop
into an adult
It also ensures the continuity of life from one
generation to the next
What happens during the
Prokaryotic Cell Cycle?
Prokaryotic cells divide asexually
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These cells possess a single chromosome,
containing genes
The chromosome is replicated
The cell then divides into two cells, a
process called binary fission
What Occurs During the Eukaryotic Cell
Cycle?
The cell cycle consists of two major phases:
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Interphase, where chromosomes duplicate and
cell parts are made.
The mitotic phase, when cell division occurs
Interphase consists of three main stages:
G1 or Gap 1
S or Synthesis
G2 or Gap 2
Cell division
cell
division
cell growth and
DNA replication
The chromosomes of eukaryotes
duplicate with each cell division
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A eukaryotic cell has many more genes
than a prokaryotic cell
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The genes are grouped into
multiple chromosomes,
found in the nucleus
The chromosomes of this
plant cell are stained
dark purple
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Chromosomes contain a very long DNA
molecule with thousands of genes
Sister chromatids
Individual chromosomes are
only visible during cell
division
 They are packaged as
chromatin.
 Before a cell starts dividing,
during S, the chromosomes
are duplicated. This process
produces sister chromatids
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Centromere
There Are Two Types of division in Eukaryotic Cells:
Mitotic Cell Division and Meiotic Cell Division
Mitotic cell division
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This is the type of cell division when a mother cell
produces two genetically identical daughter cells.
For example: If the mother cell has 46
chromosomes the daughter cells will also have 46
chromosomes.
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Cell division has two steps: Mitosis or division of
the nucleus and cytokinesis or division of the
cytoplasm.
Mitosis has four phases: Prophase, Metaphase,
Anaphase and Telophase.
Cytokinesis begins at the end of anaphase.
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The process of mitotic cell
division is used for growth,
healing, repair and
regeneration.
Meiosis
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Meiosis is the process of cell division that we use for
the formation of sex or reproductive cells.
In humans, Meiosis takes place in the reproductive
organs: the testis in males and the ovaries in
females.
In plants, Meiosis takes places in the anthers (male
structures) and in the ovary (female structure) of
the flower.
When a mother cell divides, it produces four
genetically different daughter cells with half the
number of chromosomes than the mother cell.
Chromosomes are matched in
homologous pairs
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Somatic cells of each
species contain a
specific number of
chromosomes
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Chromosomes
Centromere
Human cells have
46, making up 23
pairs of homologous
chromosomes
Sister chromatids
Gametes have a single set of
chromosomes
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Cells with two sets of chromosomes are said to
be diploid
Gametes are haploid, with only one set of
chromosomes
The
human life
cycle
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
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At fertilization, a sperm fuses with an
egg, forming a diploid zygote.
Repeated mitotic divisions lead to the
development of a mature adult
The adult makes haploid gametes by
meiosis
All of these processes make up the
sexual life cycle of organisms
mitotic cell division,
differentiation, and growth
adults
baby
mitotic cell division,
differentiation,
and growth
meiotic cell
division in
ovaries
embryo
egg
mitotic
cell division,
differentiation,
and growth
fertilized
egg
fertilization
sperm
meiotic cell
division in
testes
Homologous chromosomes carry
different versions of genes
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The differences between homologous
chromosomes are based on the fact that
they can carry different versions of a gene
at corresponding loci
Coat-color genes
Eye-color genes
Brown
Black
C
E
c
e
White
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
C
E
C
E
c
e
c
e
Chromosomes of
the four gametes
Some DNA information
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Cellular DNA is organized into chromosomes.
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The genome is all the genetic information (all
the genes) of one organism.
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A gene is a fragment of DNA that has the
information for one specific trait. Examples:
color of the eyes.
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All the variations of one gene are called
alleles: for example, blue, green, almond,
brown, red, etc.