Download Bio1A - Lec 12 slides File

Cell Cycle
Mitosis
Phases
•Define Meiosis
•Genetic composition
•Homologous chromosomes
•Stages of Meiosis I & II
•Segregation of alleles
•Independent assortment
•Homologous recombination
•Random Fertilization
•Generation of diverse gametes
Reading
Ch 12: Mitosis
Ch 13: Meiosis
Test 1: 11-12:15
Material covering
Chem  Photosynthesis
TEST instructions
Multiple Versions
Scantron provided
Sit every 3rd seat
Pencil
1 page of notes
non-scientific calculator
Scrap paper provided
Unit 2: Genetics and Molecular Biology
Tools to study the information
that creates and sustains life
The Cell Cycle
How genetic information is transmitted to
daughter cells
Focus on Eukaryotes
•Cell Cycle
•Segregation of linear
chromosomes during
mitosis
Prokaryotes
•Small circular genomes
Cell Division: What is it For?
•
•
•
•
Replacing lost or damaged cells
Growth
Genes passed on from cell to cell
Some organisms reproduce
this way (asexual)
Cell (Life) Cycle
Orderly sequence of events
• Time from one complete cell division
process to the next
• These cycles vary
• Prokaryotes cell cycles are simpler than
Eukaryotes
Prokaryotes
single circular chromosome in cytosol
• Simple such as bacteria or
blue-green algae
• They have fast cell cycles
• Remember chromosomes are
not in a membrane bound
nucleus
• Some bacterial can double
every 20 minutes
• Called binary fission – asexual
reproduction
• Identical to parent cell
Cell Cycle is Regulated
• The frequency of cell division
varies with the type of cell
• These cell cycle differences result
from regulation at the molecular
level
• The sequential events of the cell cycle are directed by a
distinct cell cycle control system, which is similar to a
clock
• The cell cycle control system is regulated by both
internal and external controls
• The clock has specific checkpoints where the cell cycle
stops until a go-ahead signal is received
The Human Genome is big!
3.4 billion base pairs
Chromosomes are really long (1-9cm)
Chromosomes condense after
interphase during mitosis
Coil, supercoil, wind etc.
1 line = 1 double stranded DNA
Chromosome (single piece of DNA)
S-phase
Also a SINGLE Chromosome,
even though duplicated
(still one piece)
Chromatid – 1 half of duplicated
chromosome – packaged for
mitosis/meiosis
When cell divides, one chromosome
goes to each daughter cell
Fig. 12-4
0.5 µm
Chromosomes
arm
DNA molecules
Duplication /
DNA synthesis
Centromere
Sister
chromatids
Separation of
sister chromatids
Centromere
Sister chromatids
Telomere
How many chromosomes?
a)0
b)1
c) 2
d)3
e)4
How many chromosomes?
a) 0
b) 1
c) 2
d) 3
e) 4
How many chromatid?
a) 0
b) 1
c) 2
d) 3
e) 4
Human Chromosomes
Autosomes
– Non-sex ch’s
– 22
Sex chromosomes
– Determine gender
– Normal female = XX
– Normal male = XY
You get 23 ch’s from
each parent
Different organisms
have diff # Ch’s
karyotype - ordered display of
metaphase chromosomes (somatic cell)
Why a pair?
• Human somatic cells (any cell other than a gamete)
have 23 pairs of chromosomes
• Compensate for defective genes
– One chromosome may have a functional gene that
compensate for a defective gene on the other
chromosome
• Generates diversity among offspring when
eukaryotes sexually reproduce
Homolgous chromosomes
•Each chromosome has many genes
•“paired” homologous chromosomes have same genes
From
Mother
Gene 1
Gene 1
Eye color
Blue
Eye Color
Brown
Gene 3
Gene 3
Gene 4
Gene 4
Height
Tall
Gene 6
Height
Tall
Gene 6
From
Father
Each Somatic cell has 2 copies of every gene
Cells have chromosomes –
one or more
karyotype - ordered display of
metaphase chromosomes (somatic cell)
•Many organisms (humans) have 2 of each chromosome (see above)
•The chromosomes that are the same are called homologous
(example each ch. 1 is homologous to every other ch1)
•Because we have 2 we refer to it as a “homologous pair”
•Other organisms can have different numbers of copies (like legs  1
leg, 2 legs, 3 legs, 4 legs etc.) and so if not 2 then are not referred to
as a pair, but the idea is the same, they are all the same chromosome
= they are homologous chromosomes
Ch1a & ch1b are?
Ch1a Ch1b
a) Exactly the same
b) Homologous
c) Non-homologous
d) Have different genes
X1
x2
Y1
y2
Ch2a
Z1
Ch2b
z2
Ch Y
Ch X
Q
Ch1a & ch2a are?
Ch1a Ch1b
a) Exactly the same
b) Homologous
c) Non-homologous
X1
x2
Y1
y2
Ch2a
Z1
Ch2b
z2
Ch Y
Ch X
Q
Gene 1
Gene 1
Gene 2
Gene 2
Gene 3
Gene 4
Gene 3
Gene 4
Gene 5
Gene 5
Gene 6
Gene 6
n=1
diploid 2n = 2
Meiosis
Results in gametes
Unequal division of DNA
Reduction in DNA
Gene 1
Gene 2
Gene 1
Gene 2
Gene 3
Gene 4
Gene 5
Gene 3
Gene 4
Gene 6
Gene 5
Gene 6
Haploid
n=1
Gametes: Cells for sexual reproduction
• Produced in specialized organs, ovary or testes
• Gametes (sperm or egg) contain a single set of
chromosomes
• Meiosis  reduction in chromosome number
• Humans (and most animals) have 2 of each chromosome, Not
all organisms do though (1a & 1b)
• Big variation in the number of non-homologous
chromosomes. Humans have 23 non-homologous
chromosomes.
n, ploidy, (& C)
n = # of non-homologous ch’s
Ch 1, 2, 3,……8  n = 8
Ploidy – sets (versions) of n
For every chromosome
1a, 1b, 1c, 1d  4n or tetraploid
= 4 different versions of ch 1
DNA Content (C)
(aka chromosome number)
C = amount of DNA (strands, pg…)
Definition: Gametes have 1C of DNA
Ploidy and n are 2 different pieces of information
Unrelated but…
For convenience they are often combined
You will hear 2n, 4n, 6n this refers to ploidy
n is less important
Like how many volumes makes up the dictionary. All the information
in a single book, or the same information in 5 smaller books.
Although more chromosomes usually means more information.
n = the number of different / non-homologous
chromosomes in a cell of the organism
This number NEVER changes
Example:
n=3
3
1
Because there are ch1’s
ch2’s and ch3’s
2
1
3
2
For your convenience, homologous
chromosomes are of the same size
Cells of a Sexual Organism
• Diploid (2n)
– Cells contain 2 homologous sets of chromosomes
– All somatic cells
• Haploid (n)
– Cells contain a single set of chromosomes
– Sex cells (gametes)
• Sperm or Egg
Ways of describing copy number
The way ploidy is stated is along with “n”
Because n is always the same we say ___n is the ploidy.
1n for
2n for
3n for
4n for
1 version of each ch
2 versions of each ch
3 versions of each ch
4 versions of each ch
=
=
=
=
haploid
diploid
triploid
tetraploid
(note: doesn’t
quite make sense
in math terms,
but oh well)
Remember the gene combination determines the trait?
TT = Tall
Tt = Tall
tt = short
This is why ploidy is important. This is only the case
because cell are diploid. If cell were tetraploid the the
trait would be determined by 4 alleles.
TTTT
TTTt
TTtt
Tttt
tttt
Or even T T’ t t’
and whatever that would mean appearance wise
…maybe blue, green, yellow, orange = brown
How many chromosomes?
a) 1
b)3
c) 6
d)12
How many diff / non-homologous
chromosome pairs?
What is n?
a) 1
b)3
c) 6
d)12
3
1
2
1
3
2
Ploidy?
a) 1n
b)2n
c) 3n
d)6n
3
1
2
1
3
2
How many chromosomes?
a)1
b)3
c) 6
d)12
What is n?
a) 1
b)3
c) 6
d)12
1
2
3
1
2
3
Ploidy?
a) 1n
b)2n
c) 3n
d)6n
What is n?
a)1
b)3
c) 6
d)12
Aster
Centrosome
Centrioles
= DNA sequence
= DNA binding protein
& motor protein
2 Broad phases
1. Interphase –
• the majority of a cell’s life cycle
• Period where the “normal”
activity of a cell occurs
• Preparation for cell division
• Called inter- (in between) because
it occurs between cell divisions
• DNA doubles
– everything doubles
2 Broad phases
2. Mitosis - Cell division
• very short period
• DNA is divided and the cell
splits
• Most of the relevant events
occur during mitosis so we
spend more time talking about
the steps here, even though it is
actually a much shorter time.
Cell division
Process where cell divides into 2 daughter cells
• Mitosis - Most cell division results in daughter
cells with identical genetic information, DNA
• Meiosis - A special type of division produces
nonidentical daughter cells (gametes, or sperm
and egg cells)
Small portion of the cell cycle
Phases of the Cell Cycle
Interphase
• G1
• S – DNA Replication
• G2
Mitotic (M) phase
Chromatid segregate
• Prophase
• Prometaphase
•
•
•
•
Metaphase
Anaphase
Telophase
Cytokinesis
Examples of cells that cease to divide:
RBC’s, skeletal muscles, Cardiac
muscle & typical neurons
Hallmarks – no visible chromosomes
Prophase (& Prometaphase)
• Chromosomes “super-coil”
now can be seen (2 sister
chromatids)
• Nuclear membrane disappears
• Mitotic spindle microtubules
from and attach to sister
chromatid begins to form
• Centrosomes
- centriole pair move to
opposite poles
- & surrounding protein &
microtubules
Visible chromosomes
• Mitotic spindle fully formed
• Centromeres line up “single
file” at imaginary equatorial
plate
• One spindle microtubule
attaches to each sister
chromatid
Visible chromosomes line up
• Sister chromatids
separate “Centromeres
divide”
• Each daughter
chromosome pulls
towards a pole at
centromere
• Cell elongates
Trailing arms
Opposite of prophase
• Chromosomes have reached
poles
• Chromatids uncoil back into
chromatin
• Nuclear envelope forms
• Spindle disappears
• Cytokinesis occurs
• Cleavage furrow forms
2 nuclei 1 cell
Cytokinesis
• Occurs at the same
time as telophase
Contractile Ring
• Cytoplasm divides
• Parent cell now divided
into 2 daughter cells
identical to
parent cell
Back to
Interphase
Interphase
G1
S – DNA replication
S
G2
Mitosis
Prophase
Nucleus disappears
Centrosomes move to poles
Prophase
Centromeres
Centrosome
Metaphase
Duplicated chromosomes line up single file
Metaphase
Kinetochore
Aster
Duplicated chromosomes line up single file
Anaphase
Chromatids walk along the microtubules
one sister chromatid copy to each side
Telophase
Opposite of prophase
• Nucleus
reappears
• Chromosomes
decondense
Cytokinesis
• Occurs simultaneously, division of the cyoplasm
Telophase
Cytokinesis
• Occurs simultaneously, division of the cyoplasm
Interphase
After Mitosis: 2 daughter cells identical to original cell
When does DNA begin to condense?
a) Gap 1
b) S
c) G2
d) Prophase
Interphase
Prophase