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A Darwinian View of Life
I. Darwin’s Contributions
II. Mendel's Contributions
III. The Cellular Context
III. The Cellular Context
A. Cell Structure/Function Review
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane:
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest by protein
photosystems and protein
enzymes in chloroplasts AND/OR
cellular respiration (protein
enzymes in cytoplasm and
mitochondria).
ATP
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest:
ATP
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest by protein
photosystems and protein
enzymes in chloroplasts AND/OR
cellular respiration (protein
enzymes in cytoplasm and
mitochondria).
3. Energy used to catalyze
reactions:
ATP
Endoplasmic
Reticulum
ribosome
RNA
PROTEIN
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest by protein
photosystems and protein
enzymes in chloroplasts AND/OR
cellular respiration (protein
enzymes in cytoplasm and
mitochondria).
3. Energy used to catalyze
reactions… often building proteins
by protein synthesis (reading
DNA and making RNA and protein)
ATP
Endoplasmic
Reticulum
ribosome
RNA
PROTEIN
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest by protein
photosystems and protein
enzymes in chloroplasts AND/OR
cellular respiration (protein
enzymes in cytoplasm and
mitochondria).
3. Energy used to catalyze
reactions… often building proteins
by protein synthesis (reading
DNA and making RNA and protein)
4. Energy used for cell division.
ATP
Endoplasmic
Reticulum
ribosome
RNA
PROTEIN
III. The Cellular Context
A. Cell Structure/Function Review
1. Membrane: regulates what gets
in/out, largely through protein
channels.
2. Energy Harvest by protein
photosystems and protein
enzymes in chloroplasts AND/OR
cellular respiration (protein
enzymes in cytoplasm and
mitochondria).
3. Energy used to catalyze
reactions… often building proteins
by protein synthesis (reading
DNA and making RNA and protein)
4. Energy used for cell division
Endoplasmic
Reticulum
ribosome
RNA
DNA (genes) are recipes for proteins, and
proteins are critical to cell metabolism,
growth, reproduction, regulation of gene
action, and response to the environment.
PROTEIN
ATP
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin, either:
unreplicated (one DNA double-helix) OR Replicated (two double-helices)
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin, either:
unreplicated (one DNA double-helix) OR Replicated (two double-helices)
A single DNA double-helix,
bound with the associated
proteins (pink), is called a
‘chromatid’.
An unreplicated chromosome
has one chromatid.
A replicated
chromosome has two
chromatids that are
IDENTICAL COPIES
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many
‘sets’ of chromosomes are there?
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many
‘sets’ of chromosomes are there?
- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n)
A
b
C
d
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n)
- we then make reference to the NUMBER of chromosomes present: “1n = 2”
A
b
C
d
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n)
- we then make reference to the NUMBER of chromosomes present: “1n = 2”
- In eukaryotes, gametes and spores are haploid (typically)
A
b
C
d
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n)
- we then make reference to the NUMBER of chromosomes present: “1n = 2”
- A haploid set is also called the ‘genome’ – representing all the genetic
information needed to encode an organism of that species.
Species
Haploid Number
Domestic cat
19
Human
23
Chicken
39
Dog
39
Water Fly
80
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- In eukaryotes, gametes and spores are haploid (typically)
- bacteria and archaeans have one circular
chromosome and so are haploid organisms that
do NOT reproduce by gamete production/fusion.
A
b
C
d
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- when haploid gametes fuse during
fertilization, a zygote with two genes for every
trait is formed. This cell is DIPLOID, 2n = 4.
A
a
b
B
C
C
d
D
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- when haploid gametes fuse during
fertilization, a zygote with two genes for every
trait is formed. This cell is DIPLOID, 2n = 4.
- NOTE that the two chromosomes
of the same color are not IDENTICAL. They
govern the same traits, but the genes that they
have for these traits can be different alleles
(forms of a gene) that influence that trait in
different ways. Chromosomes that govern the
same traits are called HOMOLOGOUS
A
a
b
B
C
C
d
D
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- Many organisms (indeed, maybe MOST flowering plant species) are
POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8).
A
A
A
a
b
b
b
B
C
C
C
C
d
d
d
D
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
- Many organisms (indeed, maybe MOST flowering plant species) are
POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8).
- when it makes
gametes/spores (with ½ the
genetic info as the parent cell),
it will make diploid gametes…
so not ALL gametes are
haploid.
A
A
A
a
b
b
b
B
C
C
C
C
d
d
d
D
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
1. chromatin: indistinguishable, diffuse chromosomes
2. chromosome: condensed strand of chromatin
3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’
of chromosomes are there?
4. Chromosomes are identified and classified by their length, banding
pattern, and position of the centromere.
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
- Interphase:
Poorly named – the cell is most active metabolically, growing, building proteins,
replicating its DNA, and preparing for division.
Chromosomes are diffuse – “chromatin” – DNA recipes are being ‘read’ and proteins
are synthesized, or DNA is being replicated.
Three substages: G1, S, G2
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
- Interphase:
G1: the cell is most active metabolically, growing and building proteins appropriate
for that cell. Cell may be “arrested” in this stage and not divide again (neurons,
muscle). If so, it is more appropriately said that the cell has entered the G0 stage.
The cell also ‘proof-reads’ and repairs DNA during this stage.
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
- Interphase:
G1: the cell is most active metabolically, growing and building proteins appropriate
for that cell. Cell may be “arrested” in this stage and not divide again (neurons,
muscle). If so, it is more appropriately said that the cell has entered the G0 stage.
The cell also ‘proof-reads’ and repairs DNA during this stage.
S: (“synthesis”) DNA replication occurs; each chromosome transitions from its
unreplicated (one DNA double-helix) to its replicated (two DNA double-helices)
state.
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
- Interphase:
G1: the cell is most active metabolically, growing and building proteins appropriate
for that cell. Cell may be “arrested” in this stage and not divide again (neurons,
muscle). If so, it is more appropriately said that the cell has entered the G0 stage.
The cell also ‘proof-reads’ and repairs DNA during this stage.
S: (“synthesis”) DNA replication occurs; each chromosome transitions from its
unreplicated (one DNA double-helix) to its replicated (two DNA double-helices)
state.
G2: Preparatory for division; in animals, centrioles are made during this period. DNA
is repaired (and errors made during replication) can be corrected before division.
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
- Interphase:
- “Checkpoints”:
The transition from G1 is critical; when a cell crosses this ‘checkpoint’ late in G1, it is
committed to dividing.
Likewise, the transition from G2 is critical, because the DNA will be passed to
daughter cells in its present state.
If these checks are poorly regulated, cells can divide prematurely, before DNA proofreading is complete. This increases the number of mutations passed to daughter
cells, leading to further problems with cell division regulation. Ultimately, cells may
keep dividing with little or no regulation, as a tumor.
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
D. Cell Division: Mitosis
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
D. Cell Division: Mitosis
LE 12-9a
100 µm
Cleavage furrow
Contractile ring of
microfilaments
Daughter cells
Cleavage of an animal cell (SEM)
LE 12-9b
Vesicles
forming
cell plate
Wall of
parent cell
Cell plate
1 µm
New cell wall
Daughter cells
Cell plate formation in a plant cell (TEM)
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
D. Cell Division: Mitosis
E. Meiosis
REDUCTION
1. Overview
DIVISION
1n
1n
1n
2n
1n
1n
1n
E. Meiosis
1. Overview
2. Meiosis I (Reduction)
There are four replicated
chromosomes in the
initial cell. Each
chromosomes pairs with
its homolog (that
influences the same
suite of traits), and pairs
align on the metaphase
plate. Pairs are
separated in Anaphase I,
and two cells, each with
only two chromosomes,
are produced.
REDUCTION
E. Meiosis
1. Overview
2. Meiosis I (Reduction)
PROPHASE I:
- leptonema: condensation begins, and “homolog
search” occurs
There are four replicated
chromosomes in the
initial cell. Each
chromosomes pairs with
its homolog (that
influences the same
suite of traits), and pairs
align on the metaphase
plate. Pairs are
separated in Anaphase I,
and two cells, each with
only two chromosomes,
are produced.
REDUCTION
- zygonema: condensation continues and homologs
align and begin to interact
- pachynema: condensation is completed, and the
homologs synapse – chemically bound along length,
and exchange of DNA between homologs occurs
(crossing over)
- diplonema: homologs begin to separate, and points
of contact (chiasma) are thought to indicate where
crossing over occurred.
- diakinesis: separation of homologs and breakdown
of nuclear envelope; attachment of spindle fibers
E. Meiosis
1. Overview
2. Meiosis I (Reduction)
There are four replicated
chromosomes in the
initial cell. Each
chromosomes pairs with
its homolog (that
influences the same
suite of traits), and pairs
align on the metaphase
plate. Pairs are
separated in Anaphase I,
and two cells, each with
only two chromosomes,
are produced.
REDUCTION
E. Meiosis
1. Overview
2. Meiosis I (Reduction)
3. Transition
4. Meiosis II (Division)
Each cell with two
chromosomes divides;
sister chromatids are
separated. There is no
change in ploidy in this
cycle; haploid cells divide
to produce haploid cells.
DIVISION
5. Modifications in anisogamous and oogamous species
III. The Cellular Context
A. Cell Structure/Function Review
B. Chromosomal Terminology
C. The Cell Cycle
D. Cell Division: Mitosis
E. Meiosis
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory of inheritance
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
Sutton and Boveri (independently) saw homologous chromosomes
separating (segregating) during meiosis. If they carried genes, this
would explain Mendel’s first law.
A
a
Theodor Boveri
Walter Sutton
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
And if the way one pair of homologs separated had no effect on how
others separated, then the movement of homologs would explain
Mendel’s second law, also!
They proposed that chromosomes carry the heredity information.
A
a
A
Theodor Boveri
a
OR
AB
ab
B
b
Ab
aB
b
B
Walter Sutton
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
2. Solving Darwin’s Dilemma
Independent Assortment produces an amazing amount of genetic
variation.
Consider an organism, 2n = 4, with two pairs of homologs. They
can make 4 different gametes (long Blue, Short Red) (Long Blue,
Short Blue), (Long Red, Short Red), (Long Red, Short blue).
Gametes carry thousands of genes, so homologous chromosomes
will not be identical over their entire length, even though they may
be homozygous at particular loci.
Well, the number of gametes can be calculated as
2n
or
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
2. Solving Darwin’s Dilemma
Independent Assortment produces an amazing amount of genetic
variation.
Consider an organism with 2n = 6 (AaBbCc) ….
There are 2n = 8 different gamete types.
ABC
Abc
aBC
AbC
abc
abC
Abc
aBc
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
2. Solving Darwin’s Dilemma
Independent Assortment produces an amazing amount of genetic
variation.
Consider an organism with 2n = 6 (AaBbCc) ….
There are 2n = 8 different gamete types.
And humans, with 2n = 46?
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory
2. Solving Darwin’s Dilemma
Independent Assortment produces an amazing amount of genetic
variation.
Consider an organism with 2n = 6 (AaBbCc) ….
There are 2n = 8 different gamete types.
And humans, with 2n = 46?
223 = ~ 8 million different types of gametes.
And each can fertilize ONE of the ~ 8 million types of gametes of
the mate… for a total 246 = ~70 trillion different chromosomal
combinations possible in the offspring of a single pair of mating
humans.
F. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal
theory
2. Solving Darwin’s Dilemma
3. Model of Evolution – circa 1905
Sources of Variation
Independent Assortment
Causes of Change
 VARIATION 
NATURAL SELECTION