DNA and Mitosis review/Meiosis How do your cells divide?

DNA and Mitosis review/Meiosis

How do your cells divide?

A few words before we start…..

• Haploid: half of a full set (only 1 set of DNA)• Diploid: full set (1 set from each parent (2 sets)

A Cell’s Life

Why Do Cells Divide?

Growth

Damaged cells

Sex cells

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Cell Reproduction

is either sexual or asexual

Asexual Reproduction(one parent)

• Binary Fission-

• Budding

• Vegetative Propagation

• Regeneration Adva

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Asexual reproduction

• Advantages:– Doesn’t require a mate– Takes less time

• Disadvantages:– All offspring are the same (genetically)

Sexual Reproduction

• 2 “parents” or 2 sets of DNA• Examples: humans, plants, dogs

• Advantages– DIVERSITY!!!!!!!!!!

• Offspring are genetically different from parents.

• Disadvantages?– Need a mate– Takes longer

Sexual reproduction

DNA Replication

• Before a cell can divide the

DNA must replicate (make a copy of

itself)

DNA Replication

• Making a new strand of DNA is actually quite easy.

• Replication occurs in 3 easy steps…

1. DNA Unzips

• An enzyme (helicase) unzips the molecule

• The enzymes breaks the hydrogen bonds that hold the nitrogen bases together.

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DNA Replication DNA Unzips

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Left Strandof Original DNA

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2. Base Pairing

• Complementary bases match with each DNA strand in the open helix– DNA polymerase

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DNA Replication Base Pairing

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DNA Strand




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3. DNA Zips Up

• An enzyme (ligase) zips the new molecules back up.

DNA Replication

• Voila!• Two identical strands of DNA!

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DNA Replication Review

Step 1 Step 2 Step 3

Remember - All this takes place in INTERPHASE

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Now that DNA has replicated, we are ready to begin Mitosis (nucleusof the cell divides)

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Interphase: Parent Cell, chromosomes replicated

Prophase: Chromatin condenses into chromosomes, nuclear envelope disappears, centrioles move to opposite poles, spindle fibers form.

Metaphase: Chromosomes align on the equator

Anaphase: Chromosomes separate and chromatids are pulled to opposite poles

Telophase: DNA uncoils, nuclear membrane reappears

Cytokinesis• Cleavage (indention in cell

membrane) or cell plate formation occurs.

• Cell divides.

Animal Cell Plant Cell

Mitosis Animation

It’s all about the chromosomes!

– There are 46 in human body cells– The number of chromosomes remain

constant during Mitosis

Which Cells Go Through Mitosis?

Growth

Repair

Work

Somatic (body) cells:Cells which help the body in:

Mitosis Review 1. Is the beginning parent

cell diploid or haploid (2n or n)?

2. Are the daughter cells diploid or haploid (2n or n)?

More Mitosis Review

3. How many daughter cells are produced?

4. Are the resulting daughter cells different from the parent cell?

More Mitosis Review

5. Are the resulting daughter cells different from each other?

6. How many chromosomes are in a human parent cell?

7. How many chromosomes are in a human daughter cell?

More Mitosis Review

8.What types of cells are produced by mitosis?

9. Why (when) does a cell go through mitosis?

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Meiosis

Sexual Reproduction (two parents)

Why Meiosis?

• Meiosis - –The production of gametes

Interphase• Cell growth

• DNA replication sister chromatids held together by centromere

Prophase I• The chromosomes coil

up and a spindle forms.• Homologous

chromosomes line up with each other gene by gene along their length, to form a four-part structure called a tetrad.

Prophase I – crossing over• Crossing over occurs

between homologous chromosomes new genetic combinations that are different from the parent.

Metaphase I

• The spindle fibers pull the tetrads into the middle, or equator of the cell.

• There is no rule to who is on left or right side independent assortment.

Anaphase I• Homologous

chromosomes separate and move to opposite ends of the cell.

Telophase I• The spindle is broken

down, the chromosomes uncoil slightly, and the cytoplasm divides to yield two new cells.

• Each cell has half the DNA as the original cell because it has only one chromosome from each homologous pair. Haploid

Remember mitosis?

• Meiosis II looks just like mitosis except there is no DNA replication during interphase

Prophase II

• A spindle forms in each of the two new cells and the spindle fibers attach to the chromosomes.

Metaphase II.• Sister chromatids, are

pulled to the center of the cell and line up randomly at the equator.

Anaphase II• The sister

chromatids separate and move to opposite poles.

Telophase II• Finally nuclei reform,

the spindles breakdown, and the cytoplasm divides.

• Four haploid cells have been formed from one diploid cell– All are genetically

different from each other and from the parent cell.

How does Meiosis Occur?

Why meiosis is important

1. Forms gametes for sexual reproduction

2. Crossing over and independent assortment different genetic combinations. diversity!!!

Meiosis Review

1. Is the beginning parent cell diploid or haploid (2n or n)?

2. Are the resulting daughter cells diploid or haploid (2n or n)?

More Meiosis Review

3. How many daughter cells are produced?

4.Are the resulting daughter cells different

from the parent cell?

More Meiosis Review

5. Are the resulting daughter cells different from each other?

7. How many chromosomes are in a human daughter cell?

6. How many chromosomes are in a human parent cell?

More Meiosis Review

8. What types of cells are produced by meiosis?

Fertilization

New Individual46

Mom

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Dad

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This is how new organisms are made!!

Sexual reproduction

Meiosis

Meiosis

Sperm Cell

Egg Cell

Haploid gametes

(n=23)

Fertilization

Diploid zygote

(2n=46) Mitosis and Development

Multicellular

diploid adults

(2n=46)

Let’s reviewMitosis & Meiosis

Mitosis vs. Meiosis

Event Mitosis Meiosis

Produces 4 cells

Produces 2 cells

New cells identical

New cells different

New cells have the same number of chromosomes as parent

New cells have fewer chromosomes than parent

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Mitosis vs. Meiosis

Event Mitosis MeiosisBeginning cells diploid (2n)

Beginning cells haploid (n)

Ending cells diploid (2n)

Ending cells haploid (n)

Produces egg and sperm

Produces body cells

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DNA and Mitosis review/Meiosis How do your cells divide?

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