Unit 7 – Section 8.2 Mitosis When an organism grows larger it is

because they are adding more cells. Their cells generally remain a constant size.

Reasons for Cells to Remain SmallDiffusion - Diffusion occurs at a specific speed, the further substances have to go the longer it takes.

DNA - Nucleolus cannot keep up with the demand to copy off instructions for all the new organelles.

Surface Area to Volume Ratio - The inside volume of a cell increases faster than the outside surface area. The inside (volume) needs more nutrients than the outside (surface area) can let in or out.

No living organism or cell lives forever. They must reproduce in order for life to carry on (Cells come from pre-existing cells).

Reasons for Cells to ReproduceGrowth

- One of the characteristics of life is that all organisms grow or develop over time. New cells are necessary for this.

Replace / Repair - Cells are dying and being damaged continually, therefore they must be replaced.

Diffusion - Cells become too big to function efficiently (Nutrition & Excretion)

Unit 7 – Section 8.2 DNA Terminology

Chromatin - What the DNA is called when it is uncoiled and not easily visible (Its normal state – Interphase)

Chromosome - What the DNA is called when it is coiled and visible (During Mitosis & Meiosis)

Chromatids - What each half of a double stranded chromosome is called

Terminology continued . . .Replication - The process that copies and makes an exact replica of all DNA strands (makes them double stranded – Interphase)

Centromere - The part where the two chromatids are held together. It holds the two identical strands together so they form an “X”.

Type of Cell

# of DNA

Strands

# ofHomologues

# of Sets - Names

SomaticBody Cells

46 23 2 –Diploid

GameteSex

Cells

23 NONE 1 –Haploid

1.The weeds in this garden are spreading rapidly. What effect might this have on the flowers in the garden?

2.Suppose a change in a cell’s genes causes the cell to reproduce very rapidly. How might this increased rate of reproduction affect surrounding cells?

Cell Division - Mitosis

Cells reproduce by dividing in half.

The division of chromosomes (DNA) is called Mitosis

The division of the cytoplasm & the cell is call Cytokinesis

* A cell’s life is continuous and follows a cycle that repeats itself

* The Cell Cycle includes 3 Stages that repeatedly follow each other:

Interphase – Mitosis – Cytokinesis

Cells will grow as they live, double all of their internal parts (organelles), and split or divide equally into 2 Daughter Cells

The Daughter Cells will repeat this process and so will the next generation.

This is the basis of the cell cycle. * Different cells go through the Cell Cycle at different rates

* Minutes – Hours – Days – Weeks – Month - Year

Interphase The cell spends over 90% of its life carrying out its Normal Functions.

* This is also a Preparation time for the cell to get ready for Mitosis

Cell grows in size Replication occurs = This is the doubling of all the DNA (DNA becomes “X” shaped).

The organelles (Cytoplasm) is doubled.

* With out doubling the size – DNA – Cytoplasm we would end up with 2 half cells that could not function

Mitosis

Prophase (1st Phase) The Chromatin (DNA) is coiling up and becoming visible Chromosomes.

The Nuclear Membrane & Nucleolus dissolve and disappear.

The Centrioles move to opposite ends of the cell.

Microtubules & Microfilaments form fibers which create the Spindle.

* The Pathway for the Chromosomes to follow.

Metaphase (2nd Phase) The spindle and its fibers move the chromosomes so they are lined up in the middle of the cell between the centrioles.

The spindle fibers attach the chromosomes to the centrioles.

* The place on the chromosome where the spindle fibers attach is the centromere.

Anaphase (3rd Phase) The centrioles on each opposite end of the cell pull on the centromeres.

They divide and each chromatid is pulled in an opposite direction.

* This is very rapid and is the shortest phase.

Telophase (4th Phase) The two clusters of chromatids on each side of the cell start to unwind and become chromatin again.

A new nuclear membrane starts to form around the DNA clusters.

The spindle fibers disappear.* This phase is almost the opposite of Prophase

Cytokinesis* This takes place immediately after Mitosis.

The cell elongates and starts to pinch in the middle.

The cytoplasm divides itself as organelles are separated to opposite sides.

* In plant cells a new cell wall forms down the center dividing the cell in half.

Once the cell has divided into two, they are both in interphase and start the process over.

Importance of the Cell Cycle (Mitosis &

Cytokinesis) All organisms start out as a single cell, this allows for Growth.

In Humans, cells naturally die off at a rate of approximately 50 million a second. Therefore, these need to be Replaced.

Injury and disease can cause extra cell loss that needs to be replaced as well.

Mitosis Phases

12--White Pipe Cleaners are Chromosomes

2-- Tan Yarn is Nuclear Membrane2-- Wooden Spools are Centrioles12-- Red Yarn is Spindle Fibers4-- Construction Paper is Organelles

* Using these parts show the stages of Mitosis in an Animal with 4 Total Chromosomes (2 Pairs)

Meiosis

A process of Nuclear (Chromosome) Division creating daughter cells with the haploid (1 set) number of chromosomes.

Meiosis is used to create Gametes Only.

Male Gamete = Sperm Reproductive Cells

Female Gamete = Egg

Meiosis only occurs in the Reproductive Organs (Gonads). Mitosis occurs throughout the entire body.

Male Gonad = Testes Reproductive Organs

Female Gonad = Ovaries Gametes must contain the Haploid # of Chromosomes so when they unite the new individual will contain the correct information

( 23 Sperm + 23 Egg = 46 New Individual )

All cells in the Body contain the Diploid # (2 sets) of Chromosomes.

Meiosis is used to create Gametes from these cells

** Meiosis makes Gametes in the Gonads

Meiosis has two separate divisions ( I & II ) and will create four individual cells.

Human Female Karyotype

Human Male Karyotype

Mitosis Meiosis

Purpose:

Make new cells or replace worn out cells

Where:

Throughout the entire organism (anywhere cells are needed– Somatic Cells)

Genetic Significance:

The products (daughter cells) are identical to each other and to the cell they originated from. Therefore they are clones.

Purpose:

Make gametes (sperm & egg cells)

Where:

Reproductive Organs (ovaries & testes—Gametes)

Genetic Significance:

The products (sperm & egg) are genetically different from each other, the genetic material is rearranged during and after meiosis (end product has genetic variation)

Mitosis Meiosis

Occurs everywhere in the body (Somatic Cells)

End up with 2 Diploid Cells Identical to the Parent Cell

Has only 1 Division Mitoisis is part of a repeated Cell Cycle

All Chromosomes move independently

Occurs only in the Gonads (Gametes)

End up with 4 Haploid Cells Different from the Parent Cell

Has 2 Divisions Meiosis is a one time process for a cell

Synapsis occurs and forms Tetrads (Prophase I )

Meiosis I This first division of DNA separates the Homologous Chromsomes

(Diploid 2 sets Haploid 1 set)Interphase - Replication occurs = Doubling of the DNA

(single strands become double “X”)

* There is no growth or doubling of the cytoplasm like Mitosis. These cells have no “normal function” except to be turned into Gamates.

Prophase I - Chromatin is coiling up and becoming visible as Chromosomes.

- Nuclear Membrane & Nucleolus dissolve & disappear.

- Centrioles move to opposite ends of the cell.

- Spindle fibers start to form. * Chromosomes find their homologue and pair up, forming a Tetrad, this is called Synapsis.

Metaphase I - The spindle fibers move the Tetrads (Homologous Pairs) toward the middle of the cell in a line.

- The spindle fibers attach one chromosome to one centriole and the other chromosome to the other centriole.

Anaphase I - Each centriole pulls one chromosome of the Tetrad in opposite directions.

( The two sets are being divided )Telophase I - Two clusters of chromosomes form on each end of the cell & a new nuclear membrane forms around each.

- Chromosomes may uncoil forming Chromatin

- Spindle fibers disappear.

Cytokinesis I - The cell elongates and starts to pinch together in the middle.

- The cytoplasm is divided into two separate cells

- Males: Equally but with only ½ the normal amount.

- Females: Unequally, one cell gets all of the cytoplasm.

Meiosis II

This 2nd Division separates the Chromatids “X’s” of the remaining chromosome

There is no real Interphase between Meiosis I and Meiosis II (No growth – Replication – or Organelles made).

Both cells from Meiosis I go through Meiosis II

Prophase II, Metaphase II, Anaphase II, & Telophase II are basically the exact same as Mitosis.

The only real difference is the chromosome # is already Haploid and Organelle #’s are different.

End result is 4 Cells, each with only 23 (Haploid) Single-Stranded Chromosomes. They are now Gametes.

Spermatogenesis Oogenesis

Interphase Interphase

23X

23I

23I

23I

Meiosis I Meiosis I

Meiosis II Meiosis II

4 Haploid Gametes

1 Haploid Gamete

3 PolarBodies

Unit 7 – Section 10.2 Forming Tetrads in Synapsis causes two genetic events to occur, they are Crossing Over and Non-Disjunction

Crossing Over - Happens in Prophase I of Meiosis.

- When parts of Homologous chromosomes switch from one chromosome to the other (Information from the maternal chromosome is placed on the paternal chromosome and vice versa).

- Crossing over causes more variety in the offspring because it switches information around between homologous chromosomes

* It is estimated that there are 2-3 cross overs per pair of chromosomes during each Prophase I

Non-Disjunction - Happens in Anaphase I of Meiosis. - Failure of the Homologous chromsomes to separate properly.

- One of the spindle fibers break and the whole tetrad is pulled to one side.

- The result is gametes that have either 22 or 24 chromosomes. The zygotes that result from these gametes will have 45 or 47 chromosomes (usually the zygote doesn’t live)

** It causes Genetic Disorders or conditions that usually have a negative developmental effect such as:

Down SyndromeTurner’s SyndromeJacob’s SyndromePatau’s SyndromeMetafemalesKlinefelter’s Syndrome