Download Cell Division, Part I: Mitosis

Cell Division, Part I: Mitosis
What is function of mitosis?.
Summary of mitosis
1. exact replication of ___________________
2. replicated chromosome:
3. Cell splits. This is called ______________.
The Chromosome
What is a chromosome?
What is function of proteins in the
chromosome?
How many chromosomes are
contained in a human cell?)
A primary task during cell division is
replication of the chromosomes
1
Mitosis & Cytokinesis are part of the cell cycle
G1 –
S–
G2
–
M–
Replication of the Chromosomes
During
stage of Interphase
The two DNA strands separate & each acts as a "template"
What is a template?
Replicates remain attached for a while
- what are these replicated chromosomes called?
2
Four Stages of Mitosis
1. Prophase
 Chromatin condenses into: ________________________________
________________________________________________________
 Nucleolus and nuclear membrane ___________________________
_________________________________________________________
 spindle microtubules ______________________________________
2. Metaphase
 Chromosomes line up _____________________________________
______________________________________________________
______________________________________________________
3. Anaphase – _______________________________________________ fibers
toward the ends of the cell (opposite poles). The __________ _________ are
separated from each other, they are now considered to be _______________
4. Telophase – ____________have reached opposite ends of the cell. The
______________ disassemble. Chromosomes return to less coiled ________
state. __________ ________ begins to form around the chromosomes at the end
of each cell. ____________ begins.
Cytokinesis - Completes __________. Cytoplasm of a cell and
its organelles separate into 2 new daughter cells. Animal cells:
__________divides when cleavage furrow deepens until the
parent cell pinches into _____________ which are now in
Interphase.
How does cytokinesis differ in plants? Material for new cell
wall called __________ gather & fuse along middle (______)
of cell, between 2 nucleus forming ___________________.
3
Muscle cells: mitosis without cytokinesis
 Once formed, muscle cells can increase in _________________.
 Become ____________. A cell that has many nuclei is called a __________
(pronounced “sin-SISH- ium”).
Why multiple nuclei in each cell? Each skeletal muscle cell is made up of
many precursor cells, called ________, which have fused together to form one
long, thin cell with many nuclei. The muscle cells need these multi-nuclei to
multi-task. i.e.: _____________________.
Control of the Cell Cycle
Different cell types divide at different rates
Rapid dividers
skin
intestinal lining
hair follicles
Slow dividers
muscle cells
neurons
liver cells
When good cells go bad: CANCER
= Mitosis out of control
 Results from ___________ (usually several) in a single cell
E.g. genes involved in regulating growth or suppressing tumors
Tumor = ______________ of tissue
What is a Malignant tumor? Cancer, _________________ that can invade other
tissues
Unusual properties of cancer cells
 Abnormal growth- ________ is uncontrolled as cell growth is not inhibited
when the _____________________ with another cell
 Cells are undifferentiated
4
Example – Lung Cancer
160,000 deaths/year
80-90% caused by smoking
Only 12-15% of patients cured
``A cigarette is a euphemism for a cleverly crafted
product that delivers just the right amount of nicotine
to keep its user addicted for life before killing the
person.''
Gro Harlem Brundtland
Director General, World Health
Organization
5
Cell Division, Part II: Meiosis
Special type of cell division to produce __ ________________
What is a gamete? _____________
So, where in the body does meiosis occur?________________
Meiosis produces daughter cells with half the normal chromosome number
Somatic cells (non-gametes) have ____ chromosomes . . .
. . . but there are only ____ “types”
chromosomes of same type are said to be ____ _________________
Why do chromosomes come in homologous pairs? _______________
____________________________________________________________
The 23 pairs of chromosomes can be divided into 22 _________________
and one pair of ___________________________
Meiosis is cell division that reduces chromosome number by half
Gametes (23 chromosomes) are called ________________
Somatic cells (46 chromosomes) are called _________________
6
Meiosis involves 2 cell divisions
Meiosis I
 in first metaphase chromosomes line up in homologous pairs
what does this picture represent?
XX
XX
XX
XX
7
Meiosis II
 ___________ separate just as in mitosis (but with _______ the number of
chromosomes)
X
X
Meiosis and Fertilization increase genetic variability in several ways
1. Crossing Over
2. Independent Assortment (Random Assortment of Homologues)
3. Fertilization
8
IGNORE
# homologous pairs
# combinations
22
24
25
223
2
4
5
23
= 4
= 16
= 32
= 8,388,608
Errors in Meiosis
Non-disjunction: chromosomes don’t separate
Trisomy 21 most common chromosome number
abnormality
Why?
Meiosis and sex determination
Non-disjunction of ______________ shed light on mechanism of ____________
Normal ♀
Normal ♂
XX
XY
Is sex determined by number of X’s or Y’s?
XO
XXY
9
10
HEREDITY
Early Ideas
 Blending inheritance- Short-lived theory that the sperm and egg of parent
organisms contained a sampling of the parent's "essence" and that they
somehow blended together to form the pattern for the offspring.

 What is it? The theory of blending inheritance referred to an actual blending
of the genetic material (i.e. in modern terms, alleles would blend together to
form a completely new allele).
Later replaced by the view of _____Mendelian_____ inheritance
 Inheritance of acquired characteristics
What is it? This theory proposed that genetic traits of a parent are passed
onto offspring on the basis of modification from use. One classical example is
the giraffe neck; which was proposed to be passed on to F1 and F2
generations based on the parent's strain to higher trees.
The first modern geneticist? ____Gregor Mendel________________________
1866 - “Treatise on Plant Hybridization”
Mendel’s Experiment:
P1
Purple (PP) x
P
p
P
Pp
Pp
White (pp)
P
Pp
Pp
11
Mendel concluded:
To explain his results, Mendel formulated a hypothesis that included the
following:
1. that the inheritance of each trait is determined by "units" or "factors" that are
passed on to descendents unchanged (these units are now called genes )
2. that an individual inherits one such unit from each parent for each trait (the
principle of segregation)
3. that a trait may not show up in an individual but can still be passed on to the
next generation.
* According to the principle of segregation, for any particular trait, the pair of
alleles of each parent separate and only one allele passes from each parent on to
an offspring. Which allele in a parent's pair of alleles is inherited is a matter of
chance. We now know that this segregation of alleles occurs during the process
of sex cell formation (i.e., meiosis ).
* According to the principle of independent assortment, different pairs of alleles
are passed to offspring independently of each other. The result is that new
combinations of genes present in neither parent are possible. For example, a pea
plant's inheritance of the ability to produce purple flowers instead of white ones
does not make it more likely that it will also inherit the ability to produce yellow
peas in contrast to green ones. Likewise, the principle of independent assortment
explains why the human inheritance of a particular eye color does not increase or
decrease the likelihood of having 6 fingers on each hand. Today, we know this is
due to the fact that the genes for independently assorted traits are located on
different chromosomes .
* If an organism has two unlike factors (we call them alleles) for a characteristic,
one may be expressed to the total exclusion of the other (dominant vs
recessive).
12
Modern Terminology for Mendel’s discoveries
Different forms of a gene are called __alleles_________
example: eye color: blue, brown
flower color: purple, white
The combination of alleles carried by an individual is her ____genotype_____
example: BB- homozygous dominant for brown eyes
Bb- heterozygous for brown eyes
What is the relationship between the two genes you have for a trait and the
homologous chromosomes? The genes are carried on the homologous
chromosomes.
The appearance of an individual is her ___phenotype_____.
Why did F2 generation have a 3:1 ratio?
F1
Pp
x
Pp
(note that both parents
are heterozygous)
meiosis
The Punnett Square makes it easy to determine outcome of crosses
P
p
P
PP
Pp
p
Pp
pp
13
The Test Cross
What is the genotype of the white-flowered plant? pp
What is the genotype of the purple-flowered plant? Pp, PP
Mendel also did crosses involving two traits
this is called a ____dihybrid cross______
where: R = round (dominant) & r = wrinkled seeds (recessive)
purple flower, round seeds
x
Punnet Square for dihybrid cross
PPRR x pprr
PR
PR
Pr
pR
Pr
PPRR PPRr PpRR PpRr
PR
PPRR PPRr PpRR PpRr
PR
PPRR PPRr PpRR PpRr
PR
PPRR PPRr PpRR PpRr
14
white, wrinkled
Phenotype
General Genotype
9 Purple, Round Seed
P_W_
3 Purple, Wrinkled Seed
P_ww
3 White, Round Seed
ppW_
1 White, Wrinkled Seed
ppww
Beyond simple Mendelian genetics
1.
Linked Genes
Genes assort independently only if they are on different chromosomes
If the are on different chromosomes
They can line up like this….
or they can line up like this
 Gametes 
but if the alleles are on the same chromosome, how many alleles can be
produced?
15
Linked and Sex-Linked Genes
So, what would a dihybrid cross look like if the genes for flower color and seed
shape were on the same chromosome, i.e. if they were linked?
purple flower, round seeds
x
white, wrinkled
PPRR
pprr
Linked genes only produce 1 allele for each set of traits:
If P is linked to R, only PR gametes are possible.
If p is linked to r, only pr gametes are possible.
PR
PR
pr
PPRR PpRr
pr
PpRr
pprr
Instead of a 9:3:3:1 phenotypic ratio with independent assortment the ratio is
3:1.
… unless crossing over occurs
2.
Incomplete dominance
= Intermediate inheritance where both heterozygous alleles are expressed
e.g. snapdragon flower
CC
red
x
C’C’
with incomplete dominance,
the red doesn’t completely
express. The resulting color
is pink.
white
16
Is incomplete dominance the same thing as the “blending inheritance” as
envisioned by 19th century biologists? No. I n the case of blending, there
would be no chance of red or white showing in future generations.
Incomplete dominance doesn’t alter the genotype of the plant, red or white
can still be expressed.
3.
Codominance
= __both alleles are expressed: red flowers with white spots.
e.g. ABO blood type
4.
Polygenic inheritance
= ____multiple gene inheritance______
e.g. skin color depends on melanin concentration
Multiple Gene (Polygenic) Inheritance
Assuming 2 alleles per gene (locus),
# genes
1
2
3
n
# genotypes
3
9
27
3n
17
5.
Pleiotropy
= a gene that affects more than one phenotype
Albinism




6.
white skin & hair
hypersensitivity to light
poor vision
poor eye muscle control
Sex-Linked genes
= ____genes carried by either sex chromosome_______
X-linked recessive traits are always expressed in males
 red-green color blindness
 hemophilia
18