Download Cell Division - El Camino College

How much do you remember
about cell division?
Meiosis insures that
A.
Each gamete receives the same genes
B.
Chromosome number is doubled in the
gametes
C.
Zygotes produced by fertilization have the
normal number of chromosomes
D.
All paternal chromosomes end up in the same
gamete
1
Which of the following is not true about
interphase?
A.
B.
C.
D.
The cell grows larger during interphase.
Chromosomes are duplicated during
interphase.
Interphase is divided into three phases.
Chromosomes segregate to daughter cells
during interphase.
2
Which of the following is true about
homologous chromosomes?
A.
Both were received from the same parent.
B.
One of each segregates to each daughter cell
during mitosis.
C.
Both stay together in meiosis I.
D.
All 23 pairs are always homologous.
© 2009 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 4/e
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Cell Division

Renewal and repair of tissues with stem
cells

Reproduction


Prokaryotes divide through binary fission
Eukaryote cell division is more complicated
© 2009 W.W. Norton & Company, Inc.
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Prokaryotes
divide through binary fission
6
Eukaryote cell division is more
complicated: Cell cycle

Cell cycle
 Series
of events in life cycle of a cell
 Two main stages

Interphase


Most cells spend 90% of lifespan in this stage
Cell division by two different mechanisms
Mitosis: occurs in nonreproductive cells, called somatic
cells
 Meiosis: occurs in sexual reproduction cells,called germ
cells

© 2009 W.W. Norton & Company, Inc.
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The Cell Cycle
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DNA Packaged as Chromosome

DNA molecules are enormously long
 Double
helix nearly 2 meters in length
DNA is tightly packaged with proteins
 Chromatin

 DNA

and proteins
Chromosome
 Tightly
packed
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Karyotype
Chromosomes are
visible during mitosis
Their number and shape
can be studied
Humans have 46
chromosomes
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Homologous Chromosomes

46 chromosomes are arranged in 23
pairs


22 pairs are autosomes


One came from each parent
Both chromosomes are homologues
1 pair are sex chromosomes

Can be homologous; XX for females

Can be different; XY for males
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Interphase: The Longest Stage

The period between divisions:
 The

cell prepares to divide
Divided into 3 stages:

G1: growth after mitosis

S: synthesis of DNA

G2: growth before mitosis
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Mitosis

Consists of

Prophase
 Metaphase


Anaphase

Telophase
Cytokinesis: division of the cytoplasm
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Prophase

Cell enters mitosis

Chromosomes condense
 Centrosomes move apart

Go to the poles of the cell
 Mitotic
spindle begins to
form
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Metaphase

Chromosomes line up

Metaphase plate

Align sister chromatids

Equal and balanced

segregation
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Anaphase

Chromatids separate
 Break
free and dragged
to opposite sides

Microtubules shorten

Result:
 Equal
segregation of
chromosomes in two
daughter cells
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Telophase and Cytokinesis

Telophase:
 Chromosomes
reach the poles
 Mitotic spindle falls apart
 Chromosomes unfold
 Nuclear membrane reforms

Cytokinesis
 Cytoplasm
is divided
 Two cells are formed
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Cytokinesis
Cytoplasm is divided
Two cells are
formed
Cancer

Tumor: inappropriate proliferation of cells
 Benign
tumor: confined to one site
 Malignant tumor: cells migrate and invade
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Cancer and Lifestyle: Lung Cancer

Environmental factors: Smoking-related cancers


Lung, oral, kidney, stomach, bladder
Tobacco smoke 40 known carcinogens
Lung cancer cells (300X)
Portrait of a cancer
Retinoblastoma:
mutation of a
gene

An inherited form of cancer

Occurs in the retina

Causes blindness

Due to missing Rb gene

A tumor suppressor gene
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Cancer: A Multi-step Process

Example: Colon cancer
 Early

polyp:
Loss of tumor suppressor gene
 Polyp:

Mutation of proto-oncogene
 Late

Polyp:
Loss of two additional tumor
suppressor genes
 Malignant

tumor:
Inactivation of p53 tumor
suppressor
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Meiosis

Used to make gametes
 Eggs
Meiosis
and sperm

Chromosome number is halved
(haploid)

Zygote is diploid after fertilization
Fertilization
Mitosis
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 involves
two divisions,
meiosis I
 DNA is replicated only before meiosis I
 meiosis I separates the homologues in a homologous pair
 meiosis II
 meiosis II separates the replicate sister chromatids

 when
meiosis is complete, the result is that one
diploid cell has become four haploid cells

Meiosis I divided into four stages
1.
Prophase I

2.
Metaphase I

3.
The paired homologous chromosomes align
on a central plane in any combination:
independent assortment
Anaphase I

4.
Homologues pair up and exchange
segments: crossing over
Homologues separate from the pairing and
move to opposite poles
Telophase I

Individual chromosomes gather at each of
the two poles
 Meiosis
II

basically a mitotic division of the products of meiosis I,
except that the sister non-identical chromatids

four stages
1. Prophase II
 new spindle forms to attach to chromosome clusters
 2. Metaphase II
 spindle fibers bind to both sides of the centromere and
individual chromosomes align along a central plane
 3. Anaphase II
 sister chromatids move to opposite poles
 4. Telophase II
 the nuclear envelope is reformed around each of the four
sets of daughter chromosomes

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Practice questions
1.
A)
B)
C)
D)
Prokaryotes reproduce new cells by
copying DNA then undergoing binary fission.
splitting in half
undergoing mitosis
copying DNA then undergoing the M phase.
2. The eukaryotic cell cycle is different from prokaryotic cell division in all the following ways except:
A) the amount of DNA present in the cells
B) how the DNA is packaged
C) in the production of daughter cells
D) the involvement of microtubules.
3. In eukaryotes, the genetic material is found in chromosomes and:
A) the more complex the organism, the more pairs of chromosomes it has
B) a few organisms have only one chromosome
C) most eukaryotes have between 10 and 50 pairs of chromosomes
D) most eukaryotes have between 2 and 10 pairs of chromosomes.
4. Homologous chromosomes:
A) are also referred to as sister chromatids
B) are genetically identical
C) carry information about the same traits located in the same places on the chromosomes
D) are connected to each other at their centromeres.
5. In mitosis, when the duplicated chromosomes line up in the center of the
cell, that stage is called:
A) Prophase
B) metaphase C) anaphase D) telophase.
6. The division of the cytoplasm in the eukaryotic cell cycle is called:
A) interphase.B) karyokinesis.C) cytokinesis.D) binary fission.
7. The cell cycle is controlled by:
A) a series of checkpoints
B) an internal clock
C) the completion of one phase triggering the next phase
D) cell size-when it grows large enough the cell cycle is triggered.
8. When cell division becomes unregulated, and a cluster of cells begins to
grow without regard for the normal controls, that is called:
A) a mutation.B) cancer.C) metastases.D) oncogenes.
9. During which stage of meiosis does crossing over occur?
A) prophase IB) anaphase IC) metaphase IID) interphase
10. The purpose of mitosis is to ____, while the purpose of meiosis is to _____.
A)
make diploid cells/make haploid cells
B)
make haploid cells/make diploid cells
C)
make cells which are either haploid or diploid/make cells which are haploid
D)
make cells which are haploid/make cells which vary in chromosome number
11. An egg and a sperm unite to form a new organism. In order to prevent the new
organism from having twice as many chromosomes as its parents:
A)
half of the chromosomes in the new organism quickly die off, leaving the correct
number
B)
half of the chromosomes from the egg, and half from the sperm, are ejected
from the new cell
C)
the large egg contains all the chromosomes, the tiny sperm only contributes
some DNA
D)
germ cells went through meiosis; the egg and sperm only have half the parental
chromosomes.
12. The diploid number of chromosomes in humans is 46. The haploid number is:
A) 138 B) 92
C) 46
D) 23.
13. In organisms that have sexual life cycles there is a time when there are:
A) 1n gametes (haploid), followed by 2n zygotes (diploid)
B) 2n gametes (haploid), followed by 1n zygotes (diploid)
C) 2n gametes (diploid), followed by 1n zygotes (haploid)
D) 1n gametes (diploid), followed by 2n zygotes (haploid).
14. The purpose of meiosis I is to:
A) duplicate all chromosomes
B) randomly separate the homologous pairs, called independent assortment
C) separate the duplicated sister chromatids
D) divide the original material into four complete haploid cells.
15. The purpose of meiosis II is to:
A) duplicate all chromosomes
B) randomly separate the homologous pairs, called independent assortment
C) separate the duplicated sister chromatids
D) divide the original material into four complete haploid cells.