Lecture 1 – Mitosis
Cell Division: the process by which cells make more cells, occurs for growth, cell replacement, healing,
and reproduction.
Mitosis
-> Mitotic cells (aka stem cells)
-> E.g. neural stem cells, follicle hair stem cells, muscle stem cells, intestinal stem calls
(all go under mitosis)
Meiosis
-> sperm and egg cells
Eukaryotes: genome large and linear, DNA in nucleus
Prokaryotes: genome small and circular, DNA in cytoplasm
Homologous Chromosome: chromosome pairs (from each parent) similar in length and gene position
Sex Chromosome: determines sex of human (XX is female, XY is male)
Chromosome: two sister chromatids attached by the centromere, two kinetochores placed on either
side of the centromere and spindle is attached to kinetochores
Interphase: 46 chromosomes to 92 chromatids but still 46 chromosomes (count by centromeres)
G1 Phase (Gap 1): growth, cellular metabolism
S Phase (Synthesis): DNA synthesize, homologous chromosomes (two, one from each parent) duplicate
at the centromeres to become sister chromatids
G2 Phase (Gap 2): preparation for mitosis, increase in size
Cells that are not actively cycling will exit the cycle from G1, entering a state "G0"
Mitosis
Prophase: chromosomes condense (thicken), centrosomes radiate microtubules and migrate to
opposite poles
Prometaphase: microtubules attach to chromosomes, nuclear envelope starts to break down
Metaphase: chromosomes attached by microtubules align in the centre of cell, nucleus has
disassembled
Anaphase: sister chromatids separate due to the microtubules pulling them to opposite sides of the cell,
these chromatids are now individual chromosomes
Telophase: nuclear envelope reforms around each group of separated chromosomes and chromosomes
condense (thicken)
Cytokinesis: cytoplasm splits to from two cells, site of split is called "contractile ring" in animals and
called "cell plate" in plants
Ploidy Levels: the number of complete sets of chromosomes in a cell is know as it's ploidy
Haploid (n): a cell with one complete set of chromosomes (e.g. sperm)
Diploid (2n): two complete set of chromosomes, one copy from each parent (e.g. somatic cells such as
skin or leaf cell)
, Lecture 2 – Meiosis, Regulation of Cell Cycle
Haploid (n): half the amount of DNA as a diploid cell, common in gametes/sex cells. They are produced
by meiosis. Two haploid cells (a mom and a dad) are fertilized so the offspring has a complete set of
chromosomes. Contains 23 chromosomes.
Diploid (2n): two times more DNA than a haploid cell, contains two sets of unique chromosomes, from
both the mother and father. Mammals contain two homologous copies of each chromosome. Produced
by mitosis. Contains 46 chromosomes
Things to remember
There is only one interphase
The first division randomly separates homologous chromosomes
The second division results in the splitting of sister chromatids
The end result 4 genetically unique haploid daughter cells
Meiosis I
Prophase I: DNA replication has already completed. Centrosomes with microtubules migrate to each
side of cell. Homologous (same chromosome but one from mom and one from dad) condense and
undergo synapsis (crossing over). The nuclear envelope begins to break down.
Two homologous chromosomes cross over forming a bivalent set of chromosomes, the point at
which they cross is called chiasma
The final product of the two crossed over chromosomes are called recombinant chromatids
Prometaphase I: spindles attach to kinetochores (on the chromosomes on centromere) by mono-
orientation, meaning two kinetochores attach to one side of chromosome and another two on the other
side of different non-sister chromosome.
Metaphase I: Homologous pairs line up in center of cell with bivalents oriented randomly.
Anaphase I: new recombinant homologous chromosomes separate but not sister chromatids.
Telophase I/Cytokinesis: daughter cells are ready to move into prophase II, each daughter cell (two)
now has only one set of chromosomes making it a haploid cell.
Meiosis II
Prophase II: the nuclear envelope from telophase I is broken down and chromosomes condense
Prometaphase II: spindles attach to kinetochores on either side of sister chromatids
Metaphase II: chromosomes align on top of each other in centre of the cell
Anaphase II: sister chromatids separate
Telophase II/Cytokinesis: nuclear envelop reforms and the cytoplasm divides creating four haploid
daughter cells
In Females
Meiosis I arrest (after two cells are formed only one is good the other is a polar body) is released
in one oocytes during each menstrual cycle. Meiosis II arrest is released upon fertilization (only
one of the four daughter cells are good to become an ovum and the rest are polar body's, if not
pregnant all four are released during a period)
In Males
All four haploid cells created from meiosis are now sperm (gamete) cells
Regulation of the Cell Cycle
Cell Division: the process by which cells make more cells, occurs for growth, cell replacement, healing,
and reproduction.
Mitosis
-> Mitotic cells (aka stem cells)
-> E.g. neural stem cells, follicle hair stem cells, muscle stem cells, intestinal stem calls
(all go under mitosis)
Meiosis
-> sperm and egg cells
Eukaryotes: genome large and linear, DNA in nucleus
Prokaryotes: genome small and circular, DNA in cytoplasm
Homologous Chromosome: chromosome pairs (from each parent) similar in length and gene position
Sex Chromosome: determines sex of human (XX is female, XY is male)
Chromosome: two sister chromatids attached by the centromere, two kinetochores placed on either
side of the centromere and spindle is attached to kinetochores
Interphase: 46 chromosomes to 92 chromatids but still 46 chromosomes (count by centromeres)
G1 Phase (Gap 1): growth, cellular metabolism
S Phase (Synthesis): DNA synthesize, homologous chromosomes (two, one from each parent) duplicate
at the centromeres to become sister chromatids
G2 Phase (Gap 2): preparation for mitosis, increase in size
Cells that are not actively cycling will exit the cycle from G1, entering a state "G0"
Mitosis
Prophase: chromosomes condense (thicken), centrosomes radiate microtubules and migrate to
opposite poles
Prometaphase: microtubules attach to chromosomes, nuclear envelope starts to break down
Metaphase: chromosomes attached by microtubules align in the centre of cell, nucleus has
disassembled
Anaphase: sister chromatids separate due to the microtubules pulling them to opposite sides of the cell,
these chromatids are now individual chromosomes
Telophase: nuclear envelope reforms around each group of separated chromosomes and chromosomes
condense (thicken)
Cytokinesis: cytoplasm splits to from two cells, site of split is called "contractile ring" in animals and
called "cell plate" in plants
Ploidy Levels: the number of complete sets of chromosomes in a cell is know as it's ploidy
Haploid (n): a cell with one complete set of chromosomes (e.g. sperm)
Diploid (2n): two complete set of chromosomes, one copy from each parent (e.g. somatic cells such as
skin or leaf cell)
, Lecture 2 – Meiosis, Regulation of Cell Cycle
Haploid (n): half the amount of DNA as a diploid cell, common in gametes/sex cells. They are produced
by meiosis. Two haploid cells (a mom and a dad) are fertilized so the offspring has a complete set of
chromosomes. Contains 23 chromosomes.
Diploid (2n): two times more DNA than a haploid cell, contains two sets of unique chromosomes, from
both the mother and father. Mammals contain two homologous copies of each chromosome. Produced
by mitosis. Contains 46 chromosomes
Things to remember
There is only one interphase
The first division randomly separates homologous chromosomes
The second division results in the splitting of sister chromatids
The end result 4 genetically unique haploid daughter cells
Meiosis I
Prophase I: DNA replication has already completed. Centrosomes with microtubules migrate to each
side of cell. Homologous (same chromosome but one from mom and one from dad) condense and
undergo synapsis (crossing over). The nuclear envelope begins to break down.
Two homologous chromosomes cross over forming a bivalent set of chromosomes, the point at
which they cross is called chiasma
The final product of the two crossed over chromosomes are called recombinant chromatids
Prometaphase I: spindles attach to kinetochores (on the chromosomes on centromere) by mono-
orientation, meaning two kinetochores attach to one side of chromosome and another two on the other
side of different non-sister chromosome.
Metaphase I: Homologous pairs line up in center of cell with bivalents oriented randomly.
Anaphase I: new recombinant homologous chromosomes separate but not sister chromatids.
Telophase I/Cytokinesis: daughter cells are ready to move into prophase II, each daughter cell (two)
now has only one set of chromosomes making it a haploid cell.
Meiosis II
Prophase II: the nuclear envelope from telophase I is broken down and chromosomes condense
Prometaphase II: spindles attach to kinetochores on either side of sister chromatids
Metaphase II: chromosomes align on top of each other in centre of the cell
Anaphase II: sister chromatids separate
Telophase II/Cytokinesis: nuclear envelop reforms and the cytoplasm divides creating four haploid
daughter cells
In Females
Meiosis I arrest (after two cells are formed only one is good the other is a polar body) is released
in one oocytes during each menstrual cycle. Meiosis II arrest is released upon fertilization (only
one of the four daughter cells are good to become an ovum and the rest are polar body's, if not
pregnant all four are released during a period)
In Males
All four haploid cells created from meiosis are now sperm (gamete) cells
Regulation of the Cell Cycle
