Chromosomes and Mitosis/Meiosis

Info. On Chromosomes

Vocabulary1. Chromatin: DNA and Protein

DNA existing as thin, uncoiled strands This looks like spaghetti in the nucleus. 2. Chromosome: A visible carrier of the genetic information.

Chromosomes contain many genes. Every human cell contains 23 pairs of chromosomes.

Females: XX Males: XY3. Chromatids: are identical copies of a chromosome. sister chromatids contain the same genes and same alleles.4. Centromere: Point at which the pair of chromatids are

attached. 5. Allele: alternative forms of a gene

6. Autosomes/somatic: body cells; chromosome pairs 1-22

7. Sex Chromosomes: 23rd pair- determines sex of child

Human

Karyotype

Homologous chromosomes: Each pair is similar in size,

shape, and genetic content.

Cell CycleSteps in the cell cycle

1. Interphase: G1, S, G22. Prophase3. Metaphase4. Anaphase5. Telophase6. Cytokinesis

These are the steps in the entire cell cycle. • Each new cell has 46 chromosomes. • Cells are identical to each other: Called daughter cells

Mitosis

Mitosis if Animal cells

Mitosis in Plant Cells

Interphase• Period of cell growth• Not a true stage of mitosis• Can’t see chromosomes at first – duplication• 90% of time• G1: Normal Growth Phase• S: DNA Duplicates and Pairs together• G2: all other cell structures duplicate

Prophase

- Chromosomes become visible- Nuclear membrane dissolves- In animal cells, 2 centrioles move to opposite ends of cell - Spindle fibers between centrioles stretch across the call

Metaphase

- Double stranded chromosomes line up around center of cell

- Each centromere becomes attached to a spindle fiber- Spindle fibers link the chromatids of each chromosome

to opposite poles

Anaphase

• Each centromere divides• Two chromatids (now called chromosomes) move

toward opposite poles as spindle fibers attached to them shorten

Telophase

• Centrioles and spindle fibers start to disappear• Chromosomes uncoil/stretch out and become hard to

see• Nuclear membrane forms around each mass of

chromosomes – forms new nuclei• Cytokinesis begins - cytoplasm separates into 2 new

cells

Cytokinesis: The division of the cytoplasm after Mitosis (division of the nucleus) occurs. Final step in cell cycle.

• Animal Cell – Cytoplasm pinches apart

• Plant Cell – CELL PLATE forms between cells – before cell walls form

Checkpoints1. G1 checkpoint: decides of cell will divide

a. S phase- Interphase (where DNA

is copied). When its not the right conditions, cells

will exit S phase and stay in resting period

forever. Cells such as brain and some nerve cells

stay in resting period and never divide.

2. DNA synthesis (G ) checkpoint: Replicated DNA is checked

for errors.

3. Mitosis checkpoint: Triggers exit from mitosis. Signals G1

phase.

Cancer1. Uncontrolled growth of cells.

2.Genes contain info needed to make the proteins that

regulate cell growth and division. Mutations of these genes

can cause the proteins to malfunction and normal cell growth

and regulation is disrupted.

3.Mutations cause overproducing growth-promoting molecules, speeding

up the cell cycle. (stepping on the accelerator)

4.Inactivating the proteins that slow or stop the cell cycle (taking away the

brakes)

5.Benign: tumors in which cancer cells remained in original site, can be

removed successfully with out individuals having cancer. Inability to

Metastasize (spread). Most are not harmful. Can be removed

6.Malignant: Cancerous tumors. They will Metastasize causing

cancer. Treated with Radiation and Chemotherapy.

MEIOSIS! (p142)• http://www.cellsalive.com/meiosis.htm

a. Two Parts: Meiosis I and Meiosis II

b. Meiosis I

1. Prophase 1: Nucl. Mem. Goes away, Nucleolus goes away,

centrioles form spindles, Forms XX Tetrad ,

crossing over occurs___________

2. Metaphase 1: Chromosome PAIRS line up in the

middle

3. Anaphase 1: Chromosome pairs go towards

centrioles at opposite ends of the cell.

4. Telophase1: Chromosomes are at opposite ends

and the cytoplasm divides. (nucleolus comes back,

nucleus comes back etc…

5. cytokinesis1. Cytoplasm splits into

2 genetically different cells.

(diploid Cells= 46)

CROSSING OVER

• When portions of a chromatid (one of a pair of strands of DNA) on one homologous chromosome are broken & exchanged with the

corresponding portions on one of the chromatids of the other homologous chromosome.

• MEIOSIS II

a. Prophase 2: nucl. Mem/Nucleolus goes away, spindles

form

b. Metaphase 2: Chromosomes line up in the middle

c. Anaphase 2. Chromosomes split at centromere

Move to centrioles

d. Telophase 2: nucleolus/ nuc. Mem.

Comes back, spindles go

away, cell starts to split

e. Cytokinesis 2: cytoplasm splits

into 4 genetically

different cells.

(Haploid= 23)

http://www.youtube.com/watch?v=JKXAdwCibsA&feature=related

http://www.youtube.com/watch?v=35ncSrJOwME&feature=related 3:34

MEIOSIS CONTRIBUTES TO GENETIC VARIATION

3 Mechanisms make key contributions to genetic variation in Meiosis:

1. INDEPENDENT ASSORTMENT: - Random distribution of homologous

chromosomes during Meiosis - 8 million different gene combinations!

2. CROSSING OVER3. RANDOM FERTILIZATION:

- 70 trillion possible outcomes!

Independent Assortment

GAMETE FORMATION IN MALE/FEMALE ANIMALS

(p146)

• SPERMATOGENESIS

- Process by which sperm are produced in male animals

- Occurs in Testes

- Resulting 4 Haploid cells = SPERM

• OOGENESIS

- Process by which gametes are produced in female animals

- Occurs in Ovaries

- Resulting in larger egg or OVUM with most of the

cytoplasm to nourish developing organism.

CLONE

- Produced by Asexual Reproduction

– Genetically identical to its parents!

Parthenogenesis! - New individual develops from an unfertilized egg

(Ex: Drones – Bees)

a form of reproduction in which the ovum develops into a new individual without fertilization. Natural parthenogenesis has been observed in many lower animals. In many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to the male drones and the fertilized eggs to the female workers and queens.

It has also been observed in some snakes, fish,

and monitor lizards.