Cell Reproduction
Mitosis and Meiosis
aka Cell Division
Mitosis
New cells are produced by the
process of cell division, the
dividing of a cell into new cells.
Also, in cell division, both
nucleus and cytoplasm divide.
Mitosis Vocabulary
What is a homologous chromosome?
Refers to pairs of like chromosomes
What is diploid?
The total number of chromosomes
What is haploid?
Half the total of diploid
chromosomes
Mitosis Vocabulary…
What does “2n” represent?
This is the symbol for the diploid
number.
“n” is equal to the number of pairs of
chromosomes
How many chromosomes in humans?
46 – this is the “2n” number.
“n” = ?
Mitosis Vocabulary…
What is a parent cell?
Refers to the cell that
will go through cell
division
What are daughter
cells?
Cells that are formed
in cell division – the
result of cell
reproduction
Chromosomes
What are chromosomes?
Carrier of genetic materials, threadlike fibers found in the nucleus
What happens to the chromosomes
during cell division?
During cell division, the chromosomes
are passed to the new cells that
are formed
They are composed of genes
Chromosomes…
What are sister
chromatids?
two distinct strands that
make up chromosomes
What is a centromere?
Structure that holds the
chromatids together
Chromosomes…
What are genes?
Made up of DNA and are units
of heredity; unique to
everyone
What are traits?
Are physical and unseen
characteristics.
Examples:
physical: color of skin or eyes
unseen: blood type or
intelligence level
Chromosomes…
What are living things made of?
Made of cells that contain a certain
number of chromosomes.
Examples: body cells of an onion plant
contains 16 chromosomes
How many chromosomes does a human
have?
46 chromosomes
What is mitosis?
• Type of cell division by which
chromosomes double to form two
complete identical cells or daughter
cells
• Each daughter cell receives the same
number of chromosomes that the parent
cell had
Why do cells divide?
Cell size is an
important factor in
causing a cell to
divide
A cell will not
continue to grow
indefinitely, when a
cell reaches a
certain size, it will
divide
The Cell Cycle
Consists of 3 stages:
Interphase
Mitosis
Cytokinesis
What is interphase?
First stage of the cell cycle
“resting” stage is the period in which
cells carry out many activities
other than mitosis
Interphase is not a part or period of
mitosis; this phase precedes mitosis
and follows cytokinesis
Stages of interphase
• G1 Phase – the cell doubles in size,
enzymes and organelles, such as
mitochondria and ribosomes, roughly
double in number
• S Phase – the DNA that makes up the
chromatin replicates – chromosomes
double. Example: human chromosomes go
from 46 chromosomes to 92 chromosomes
• G2 Phase – the cell undergoes rapid growth
that prepares it for mitosis, makes the
necessary enzymes and structures
Stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Second stage of the cell cycle
What happens during prophase?
• Chromosomes come in pairs, appear
shorter and thickened
• Nuclear membrane and nucleolus
disintegrate or disappear
• Centrioles move to the opposite ends
of the cell
• Spindle fibers form at the centrioles
What happens during metaphase?
• Paired thick chromatids move to
the center or equator of the cell
and line up along the equator
• The centromere of each pair of
chromatid is attached to a spindle
fiber from the centriole
What happens during anaphase?
• Centromeres split and the spindle
fibers pull the sister chromatids
apart
• The paired chromatids are now
individual chromosomes
• Separated chromosomes are moved
towards the opposite poles of the
cells or to the ends of the spindle
fibers
What happens during telophase?
• In animal cells, cytoplasm pinches
together along the equator until two
daughter cells are formed
• In plant cells, a cell plate forms
between the 2 new cells
• Chromosomes become thread-like by
uncoiling
• Nuclear membrane and nucleolus reform
• Spindle fibers begin to breakdown
What is cytokinesis?
Third stage of the cell cycle
The division of the cytoplasm
Produces 2 new daughter cells
Animal or plant division
• Animal cells:
• The cell pinches in
on both sides to
form a cleavage
furrow.
• Plant cell:
• The cell forms a cell
plate between to 2
new cells.
What does mitosis accomplish?
• Reproduction of cells
• Equal distribution of DNA (genetic
information) to each daughter cell
• http://www.johnkyrk.com/mitosis.html
Example of mitosis
Fruit Fly has 8 diploid chromosomes
Mitosis = parent cell division into 2 daughter
cells
Fruit fly – how many chromosomes at each
phase?
Interphase – (still one cell)
Prophase - (still one cell)
Metaphase - (still one cell)
Anaphase - (still one cell)
Telophase – (two new cells)
Normal cells
Animal Cells/Diploid
Humans – 46
Cat – 38
Cow – 60
Dog – 78
Fruit Fly – 8
Goldfish – 94
Grasshopper – 14
Housefly - 12
Plant cells/Diploid
Onion – 16
Pea – 14
Apple – 34
Sunflower – 34
Plum – 48
Rice – 12
Tobacco – 48
Normal cells…
Notice that the numbers for all organisms
listed are even numbers. Chromosomes
in the body cells of all organisms occur
in pairs.
Homologous chromosomes – refers to
pairs of like chromosomes
Example: In cat cells there are 19 pairs of
chromosomes
What is cancer?
o Uncontrolled cell division
o The cell never goes into
interphase
o Always in a state of division
What factors contribute to the
development of cancer?
• Genetic malfunction where enzymes that
start and stop the cell cycle are either not
produced or are over produced
• When cells no longer respond to the
chemicals that are secreted to prevent the
overcrowding of cells. This is known as
contact inhibition
• Environmental factors: cigarette smoke,
air and water pollution, and exposure to
ultraviolet radiation
What are the steps of cancer?
1.
2.
3.
4.
5.
6.
7.
8.
Genes controlling enzyme production are
disrupted
Changes occur in the cell cycle for cell
reproduction
Environmental factors trigger the cancer cell to
grow
Cancer cells crowd normal cells preventing
nutrients form getting to the normal cells
A tumor forms
Cancer cells break away from original cancer
growth
Cancer cells enter circulatory system and
spread throughout the body
New tumors form disrupting normal organ
function
Practice quiz
What is the diploid number for human
chromosomes?
46
What holds sister chromatids together?
Centromere
What are the stages of the cell cycle?
Interphase, mitosis, cytokinesis
Practice quiz…
What are the stages of mitosis? (in
order)
Prophase, metaphase, anaphase, telophase
In what phase does the DNA double?
Interphase
In what phase do the chromosomes line up
in the center of the cell?
metaphase
Meiosis
Cell division where one diploid cell (2n)
produces four haploid (n) cells called
sex cells or gametes
These cells have half the number of
chromosomes as a body cell of a parent
Meiosis vocabulary
What is a gamete?
Male and female sex cells; the sperm
and egg
What is the male gamete?
Sperm; has 23 chromosomes
What is the female gamete?
Egg; has 23 chromosomes
Meiosis vocabulary…
What is a zygote?
A fertilized egg – has a diploid number
(2n) of chromosomes
What is sexual reproduction?
The pattern of reproduction that involves
the production and fusion of haploid sex
cells
What is a diploid cell?
Cell containing two of each kind of
chromosome from the parent
Meiosis vocabulary…
What is a haploid cell?
Cell containing one of each kind of
chromosome from the parent
What is an allele?
Gene form for each variation of a trait of an
organism. Example: gene for height can
express tall or short
Homologous chromosomes:
Pairs of like chromosomes even though the
alleles may be different – so they are not
identical chromosomes – sibling variation
The Phases of Meiosis
Meiosis I
Interphase
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Interphase
Carries out metabolic activities of the cell
Replicates its chromosomes
Precedes meiosis 1
Prophase I
• Chromosomes coil up and spindle form
• Homologous chromosomes pair up and a
four-part structure called a tetrad
forms
During prophase I…
• Tightly wound tetrads get so close to
one another that the genetic material
from one homologous pair exchanges
with the other creating new
combinations of alleles in the genetic
code
• Nuclear membrane disappears
• Nucleolus disappears
What is crossing over?
Exchange of
genetic
material by
non-sister
chromatids
during
prophase I
Results in
new
combinations
of alleles
Metaphase I
• Tetrads line up at the equator
• Homologous chromosomes are lined up in
pairs along the midline or equator of the
cell
• Spindle fibers attach to the centromere
on each pair
• The pairs are not attached to each
other
Anaphase I
• Homologous chromosomes are separated
and pulled to opposite poles of the cell
• The centromeres do not split during this
phase
• Each new cell receives only one
chromosome from each homologous pair
Telophase I
•
•
•
•
Spindle breaks down
Chromosomes uncoil
Cytoplasm divided in 2
Each cell has half the genetic
information from the original cell
• Chromosomes are still doubled
containing two sister chromatid
• Nuclear membrane reforms
• Two diploid daughter cells formed
Meiosis II
Is there an interphase in Meiosis II?
No. Chromosomes do not replicate
The cells go directly from meiosis I to
meiosis II
Prophase II
• Spindle forms in each of
the two new cells
• Chromosomes are still
coiled as sister chromatids
• Nuclear membrane
disappears
• Nucleolus disappears
Metaphase II
• Chromosomes line up at
the equator of the cell
• Spindle fibers attach to
the centromeres
Anaphase II
• Centromeres split
• Spindle fibers
pull separated
chromatids to
opposite poles of
the cell
Telophase II
•
•
•
•
•
•
Spindle fibers disappear
Chromosomes uncoil
Nuclear membrane reforms
Nucleolus reforms
Cytoplasm divides
Each cell now has half the chromosomes
that its parents had
• Four daughter haploid cells are formed
What are the two divisions of
meiosis?
Meiosis I and Meiosis II
Meiosis I
When homologous chromosomes come
together and separate
Meiosis II
The division that results in 4 daughter
cells, each with half the chromosomes
present in the original cell
What is genetic recombination?
Genetic variation
due to crossing
over and random
assortment
How many ways can
the chromosomes
line up?
2
How do you find the total number
of different kinds of sperm and
egg that can be produced?
• Take the number of pairs and place it as
the exponent with a base of 2
• Example: in humans there are 23 pairs
of chromosomes
• For sperm: 223 = over 8 billion
• For egg: 223 = over 8 billion
What is the total when
fertilization occurs?
223 * 223 = 70 trillion zygotes are possible
What is oogenesis?
Refers to the
formation of
the egg cell
What is spermatogenesis?
Refers to the
formation of
the sperm cell