The Cell Cycle, Mitosis The Cell Cycle, Mitosis and Meiosisand Meiosis

Cell ReproductionCell Reproduction

The Cell Cycle

Most of a cell’s timenot spent dividing

G 1: Gap 1 or Growth1: cell is growing after just being created

S stands for Synthesis. DNA is copied before the cell can divide again

G2 is a second growth stage as the cell prepares to divide again

Mitosis is used Mitosis is used to…. to….

Mitosis is used for Mitosis is used for asexual reproduction. asexual reproduction. To spread out in a To spread out in a habitat by making habitat by making clones.clones.

It is also used to grow It is also used to grow and develop and repair and develop and repair injuriesinjuries

This is a clone of Aspen Trees. They are all genetically identical

There are 4 Steps to Mitosis, and Interphase when cells are in the G, S and G2 parts of the cell cycle

During the S part of theCell cycle, the DNA Replicates

This creates two identicalpieces of DNA calledsister chromatids

Together the two sistersMake up a chromosome

Prophase (First phase)Occurs as the chromosomes becomevisible and the nuclear membrane begins to break down.

During Metaphase(middle phase)The ChromosomesLine up in the middle of The cell. Having beenPushed and pulled on By the spindle fibers

Spindle Fibers

Each sister chromatid attaches to different spindle fibers at the Kinetochores of the chromatids

During Anaphase (Separate)The spindle fibers shorten, pulling the sister chromatids apart to oppositeends of the cell. Once apart they are noweach called Chromosomes.

Telophase (End phase)

Two nuclei reform, and a new cell wall called a cell plate is built in plants to separate the cytoplasm of the two new daughter cells.

The two daughter cells are identicalto each other and to the parentcell which created them

Mitosis works fine for

Growth and development

Repair of damaged tissue

But it can’t be used to make egg or sperm cells because…

Egg and sperm cells (gametes) need one half the chromosomes of the parent cell

Meiosis Meiosis Sexual Reproduction in PlantsSexual Reproduction in Plants

Meiosis makes cells with 1/2 of the chromosomes as Meiosis makes cells with 1/2 of the chromosomes as the parent cell.the parent cell.

In plants this process makes either male In plants this process makes either male microsporesmicrospores that become sperm, or female that become sperm, or female megasporesmegaspores that become that become

eggseggs

This process also makes unique cells

In plants a diploid (two sets ofChromosomes) generationDoes meiosis to make a haploid (half the number of Chromosomes) generation.

Homologous ChromosomesPairs of chromosomes that control the same traits

During Meiosis the cell During Meiosis the cell goes through two goes through two divisionsdivisions

In the first one, the In the first one, the homologous cells separate, and homologous cells separate, and in the second the sister in the second the sister chromatids separatechromatids separate

Creating up to 4 cells with half Creating up to 4 cells with half the number of chromosomes as the number of chromosomes as the parent cell.the parent cell.

How does Meiosis create unique How does Meiosis create unique

cells? cells? During Prophase 1 During Prophase 1

crossing overcrossing over happens happens to the homologous pairs to the homologous pairs to create new to create new combinations of DNAcombinations of DNA

Homologous pairOne from mom, one from dad

Crossing

Over

Unique cells due to crossing over