Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5.1 Cell Increase and
Decrease
• Cell division increase the number of
somatic cells (body cells)
5.1 Cell Increase and
Decrease
• Cell division increase the number of
somatic cells (body cells)
Zygote
Trillions of cells
5.1 Cell Increase and
Decrease
• Cell division increase the number of
somatic cells (body cells)
– Mitosis:
Division of the nucleus
5.1 Cell Increase and
Decrease
• Cell division increase the number of
somatic cells (body cells)
– Mitosis:
Division of the nucleus
– Cytokinesis: Division of the cytoplasm
5.1 Cell Increase and
Decrease
• Cell division increase the number of
somatic cells (body cells)
– Mitosis:
Division of the nucleus
– Cytokinesis: Division of the cytoplasm
– Apoptosis: Programmed cell death
5.1 Cell Increase and
Decrease
• The Cell Cycle
– Orderly set of stages that occur between
the time a cell divides and the time the
resulting daughter cells divide
5.1 Cell Increase and
Decrease
• The Cell Cycle
– Interphase
• G1
•S
• G2
– Mitotic Stage
• Mitosis and Cytokinesis
5.1 Cell Increase and
Decrease
• The Cell Cycle
– Interphase
• G1
•S
• G2
– Mitotic Stage
• Mitosis and Cytokinesis
The Cell Cycle
5.1 Cell Increase and
Decrease
• Control of the Cell Cycle
– Internal and External Signals
• Signaling proteins called cyclins increase and
decrease as the cell cycle continues
– Three Checkpoints
• G1
• G2
•M
The Cell Cycle
5.1 Cell Increase and
Decrease
• Apoptosis
– Cells undergo programmed cell death
when they cannot complete mitosis or in
response to external signals.
Apoptosis
5.2 Maintaining the
Chromosome Number
5.2 Maintaining the
Chromosome Number
• Terms:
– Chromatin: tangled mass of threadlike DNA in a
non-dividing cell
5.2 Maintaining the
Chromosome Number
• Terms:
– Chromatin: tangled mass of threadlike DNA in a
non-dividing cell
– Chromosomes: condensed DNA molecules
observed in dividing cells
5.2 Maintaining the
Chromosome Number
• Terms:
– Chromatin: tangled mass of threadlike DNA in a
non-dividing cell
– Chromosomes: condensed DNA molecules
observed in dividing cells
– Diploid (2n): Cells have two (a pair) of each type
of chromosome
5.2 Maintaining the
Chromosome Number
• Terms:
– Chromatin: tangled mass of threadlike DNA in a
non-dividing cell
– Chromosomes: condensed DNA molecules
observed in dividing cells
– Diploid (2n): Cells have two (a pair) of each type
of chromosome
– Haploid (1n): Cells have half the diploid number
of chromosomes
5.2 Maintaining the
Chromosome Number
• Overview of Mitosis
– Nuclear division in which chromosome number
stays constant
– DNA replication produces duplicated
chromosomes
– Each duplicated chromosome is composed of 2
sister chromatids held together by a centromere
– Sister chromatids are genetically identical
– During mitosis, the centromere divides and each
chromatid becomes a daughter chromosome
Chromosomes and Chromatids
Mitosis Overview
5.2 Maintaining the
Chromosome Number
• Mitosis in Detail - Animal Cells
– Prophase-nuclear membrane disappears,
centrosomes migrate, spindle fibers appear
– Metaphase-chromosomes line up at metaphase
plate, associated with spindle fibers
– Anaphase-centromeres divide, sister chromatids
migrate to opposite poles, cytokinesis begins
– Telophase-nuclear membranes form, spindle
disappears, cytokinesis occurs
Mitosis in Detail - Animal Cells
5.2 Maintaining the
Chromosome Number
• How Plant Cells Divide
– Occurs in meristematic tissues
– Same phases as animal cells
– Plant cells do not have centrioles or asters
Mitosis in Detail - Plant Cells
5.2 Maintaining the
Chromosome Number
• Cytokinesis in Plant Cells
– Flattened, small disk appears between daughter
cells
– Golgi apparatus produces vesicles which move to
disk
– Release molecules which build new cell walls
– Vesicle membranes complete plasma membranes
Cytokinesis in Plant Cells
5.2 Maintaining the
Chromosome Number
• Cytokinesis in Animal Cells
• Cleavage furrow forms between daughter
nuclei
• Contractile ring contracts deepening the furrow
• Continues until separation is complete
Cytokinesis in Animal Cells
5.2 Maintaining the
Chromosome Number
• Cell Division in Prokaryotes: Binary Fission
–
–
–
–
Prokaryotes have a single chromosome
Chromosomal replication occurs before division
Cell begins to elongate to twice its length
Cell membrane grows inward until division is
complete
Binary Fission
5.3 Reducing the
Chromosome Number
5.3 Reducing the
Chromosome Number
• Meiosis
– Occurs in the life cycle of sexually reproducing
organisms
– Reduces the chromosome number
– Provides offspring with a different combination of
traits from that of either parent
5.3 Reducing the
Chromosome Number
• Overview of Meiosis
– 2 divisions, 4 daughter cells
– Cells are diploid at beginning of meiosis
– Pairs of chromosomes are called homologues
5.3 Reducing the
Chromosome Number
• Overview of Meiosis
– Meiosis I
• Homologues line up side by side at equatorsynapsis
• When pairs separate, each daughter cell
receives one member of the pair
• Cells are now haploid
Meiosis
5.3 Reducing the
Chromosome Number
• Overview of Meiosis
– Meiosis II
• No replication of DNA occurs in this division
• Centromeres divide and sister chromatids
migrate to opposite poles to become individual
chromosomes
• Each of the four daughter cells produced has
the haploid chromosome number and each
chromosome is composed of one chromatid
Meiosis
5.3 Reducing the
Chromosome Number
• Overview of Meiosis
– Fertilization
• Fertilization restores the diploid number of
chromosomes in a cell that will develop into a
new individual.
5.3 Reducing the
Chromosome Number
• Meiosis in Detail
– Genetic Recombination Occurs in Two Ways
• Crossing Over
• Independent Assortment
Crossing Over
Independent Assortment
5.3 Reducing the
Chromosome Number
• Phases of Meiosis I
– Prophase I
• Synapsis occurs, nuclear membrane breaks
down
• Homologues line up side by side and crossing
over occurs
– Metaphase I
• Homologous pairs line up at metaphase plate
such that maternal or paternal member may be
oriented toward either pole
5.3 Reducing the
Chromosome Number
• Phases of Meiosis I
• Anaphase I
• Homologous chromosomes (each still
consisting of 2 chromatids) undergo
independent assortment into daughter cells
– Telophase I
• Cytokinesis produces 2 daughter cells which
are haploid
Phases of Meiosis I
• Fig 5.12
5.3 Reducing the
Chromosome Number
• Interkinesis - period of time between Meiosis I
and Meiosis II
• Phases of Meiosis II
– Prophase II• Cells have one member of each homologous
pair
– Metaphase II
• Chromosomes line up at the metaphase plate
5.3 Reducing the
Chromosome Number
• Phases of Meiosis II
– Anaphase II
• Centromeres divide and daughter
chromosomes migrate
– Telophase II
• Nuclei form, cytokinesis
Phases of Meiosis II
• Fig 5.13
5.3 Reducing the
Chromosome Number
• Nondisjunction
– The failure of paired chromosomes or chromatids
to separate during cell division
– Results in cells with an abnormal number of
chromosomes
– Trisomy 21 (Down syndrome) is an example
5.3 Reducing the
Chromosome Number
• Genetic Recombination
– Promotes genetic variability
– Independent assortment of paired chromosomes
during metaphase I
– Crossing over in prophase I
– Both assure that gametes will contain different
combinations of chromosomes
– When fertilization occurs, the resulting offspring
will be genetically unique
Comparison of Meiosis to
Mitosis
• DNA replication occurs only once prior to either
meiosis and mitosis
• Meiosis requires two divisions, mitosis only one
• Meiosis produces four daughter cells, mitosis
produces two
• Daughter cells from meiosis are haploid, those from
mitosis are diploid
• Daughter cells from meiosis are genetically variable,
while those from mitosis are genetically identical
Comparison of Meiosis to
Mitosis
5.5 The Human Life Cycle
• Requires both mitosis and meiosis
• Meiosis in the female is called oogenesis
• Meiosis in the male is called
spermatogenesis
• At fertilization, the resulting zygote divides by
mitosis for the processes of growth and
development
• Mitosis is used for repair throughout life
Life Cycle of Humans
5.5 The Human Life Cycle
• Spermatogenesis
– Begins at puberty and continues throughout life
– Primary spermatocytes (2n) divide in meiosis I to
form two secondary spermatocytes (1n)
– Secondary spermatocytes divide in meiosis II to
produce four sperm
5.5 The Human Life Cycle
• Oogenesis
– Begins in the fetus
• Primary oocytes are arrested in prophase I
– At puberty, one primary oocyte continues the
process of meiosis during each menstrual cycle
– Primary oocyte (2n) divides in meiosis I to produce
one secondary oocyte (1n) and one polar body
• Division is unequal as secondary oocyte receives most of
the cell contents and half the chromosomes
5.5 The Human Life Cycle
• Oogenesis
– If the secondary oocyte is fertilized, meiosis II will
proceed.
• Another unequal division will occur, the egg receiving
most of the cytosplasm. A second polar body is also
formed.
– The unequal divisions allows the egg to have all
the cellular “machinery” it needs for embryonic
development
Spermatogenesis and
Oogenesis in Mammals
5.5 The Human Life Cycle
• Summary
– Spermatogenesis and oogenesis both utilize meiosis
– Spermatogenesis begins at puberty and continues
throughout life
– Spermatogenesis produces one sperm per primary
spermatocyte
• Results in production of many sperm
– Oogenesis results in one oocyte and up to three polar bodies
per primary oocyte
• Divisions are unequal, ovum receives most cell contents
– Oogenesis begins prior to birth, stops until puberty, then
resumes in a cyclic pattern
– Cyclic release of oocytes continues until menopause when
the process stops