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Chapter 10~
Chromosomes,
Mitosis, and Meiosis
Prokaryotic Cells
 Contain circular DNA molecules
Eukaryotic Chromosomes
 Nucleosome
• histone (protein) bead wrapped in DNA
• organized into coiled loops
• held together by nonhistone scaffolding
proteins
Chromosome Organization
Cell Division: Key Roles
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Genome: cell’s genetic information
Somatic (body cells) cells
Gametes (reproductive cells): sperm and
egg cells
Chromosomes: DNA molecules
Diploid (2n): 2 sets of chromosomes
Haploid (1n): 1 set of chromosomes
Chromatin: DNA-protein complex
Chromatids: replicated strands of a
chromosome
Centromere: narrowing “waist” of sister
chromatids
Mitosis: nuclear division
Cytokinesis: cytoplasm division
Meiosis: gamete cell division
The Cell Cycle
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Interphase (90% of cycle)
• G1 phase~ growth
• S phase~ synthesis of DNA
• G2 phase~ preparation for
cell division
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Mitotic phase
• Mitosis~ nuclear division
• Cytokinesis~ cytoplasm
division
Mitosis
Prophase
 Prometaphase
 Metaphase
 Anaphase
 Telophase
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Prophase
Chromosomes visible
 Nucleoli disappear
 Sister chromatids
 Mitotic spindle forms
 Centrosomes move
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Prophase
Prometaphase
Nuclear membrane
fragments
 Spindle interaction
with chromosomes
 Kinetochore develops
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Prometaphase
Metaphase
Centrosomes at
opposite poles
 Centromeres are
aligned
 Kinetochores of sister
chromatids attached
to microtubules
(spindle)
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Metaphase
Anaphase
Paired centromeres
separate; sister
chromatids liberated
 Chromosomes move
to opposite poles
 Each pole now has a
complete set of
chromosomes
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Anaphase
Telophase
Daughter nuclei form
 Nuclear envelopes
arise
 Chromatin becomes
less coiled
 Two new nuclei
complete mitosis
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Telophase
Cytokinesis
Cytoplasmic division
 Animals:
cleavage furrow
 Plants:
cell plate
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Cell Cycle regulation
Growth factors
 Density-dependent
inhibition
 Anchorage
dependence
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Cancer
Transformation
 Tumor: benign or malignant
 Metastasis
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Heredity
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Heredity: the transmission of traits
from one generation to the next
Asexual reproduction: clones
Sexual reproduction: variation
Human life cycle:
• 23
pairs of homologous
chromosomes (46);
•1
pair of sex and 22 pairs of
autosomes;
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karyotype;
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gametes are haploid (1N)/ all
other cells are diploid
(2N);
•fertilization (syngamy) results in
a zygote
Meiosis: cell division to produce
haploid gametes
Alternative life cycles
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Fungi/some algae
•meiosis produces 1N
cells that divide by mitosis to
produce 1N adults (gametes by
mitosis)
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Plants/some algae
•Alternation of
generations: 2N sporophyte,
by meiosis, produces 1N
spores; spore divides by
mitosis to generate a 1N
gametophyte; gametes then
made by mitosis which then
fertilize into 2N sporophyte
Meiosis
Preceded by
chromosome
replication, but is
followed by 2 cell
divisions (Meiosis I &
Meiosis II)
 4 daughter cells; 1/2
chromosome number
(1N); variation
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Meiosis vs. mitosis
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Synapsis/tetrad/chiasma
ta (prophase I)
Homologous vs. individual
chromosomes
(metaphase I)
Sister chromatids do not
separate (anaphase I)
Meiosis I separates
homologous pairs of
chromosomes, not sister
chromatids of individual
chromosomes.
Tetrads and Chiasmata
Origins of Genetic Variation, I
Independent assortment:
homologous pair of
chromosomes position
and orient randomly
(metaphase I) and
nonidentical sister
chromatids during
meiosis II
 nCombinations possible:
2 ; with n the haploid
number of the organism
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Origins of Genetic Variation, II
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Crossing over (prophase I):
• the reciprocal exchange
of genetic material between
nonsister chromatids during
synapsis of meiosis I
(recombinant chromosomes)
Random fertilization:
• 1 sperm (1 of 8 million
possible chromosome
combinations) x 1 ovum (1 of 8
million different possibilities) =
64 trillion diploid combinations!