Chapter 8: Cell Reproduction

Essential Question: How do organisms grow? How do cells

reproduce by cell division?

I. Chromosomes: rod-shaped structures made of DNA and proteins

A. Chromosome structure

1. Each chromosome is a single DNA molecule associated with proteins that is tightly coiled

2. Chromosomes are visible during cell division under a microscope

3. Histones: proteins that help maintain the shape of chromosomes

a) DNA wraps around the proteinsb) Helps to package DNA tightly

4. Nonhistone: proteins that do not participate in the packing of DNA but control the activity of specific regions of the DNA

5. Chromatid: one of the two identical parts of the chromosome

a) chromatids form as the DNA makes a copy of itself before cell division

b) when the cell divides, each of the two new cells will receive one chromatid from each

chromosome

6. Centromere: holds the two chromatids together until they separate during cell division

7. When the cell is not dividing the DNA is not so tightly coiled and is called chromatin

Chromosome

B. Chromosome numbers: each species has a characteristic number of chromosomes in each cell

Adder’s tongue fern = 1,262

Organism with the MOST chromosomes

1. Sex chromosomes: chromosomes that determine the sex of an organism and may carry genes for other characteristics

a) Humans: sex chromosomes are X and Y

b) females have two X chromosomes

c) males have X and Y

2. Autosomes: chromosomes that are not sex chromosomes

a) humans have 44 autosomes b) humans have 2 sex chromosomes

3. Every cell produced by sexual reproduction has two copies of each autosome (one from each parent)

4. Homologous chromosomes: two copies of each autosome

a) same size and shape

b) carry genes for the same traits (eye color)

5. Karyotype: photomicrograph of the chromosomes found in a normal human and shows the 46 human chromosomes exist as 22 homologous pairs of autosomes and two sex chromosomes

- Fold of skin above the eye- Varying degrees of mental

retardation- Short stature

- Cardiac deformities

Down Syndrome (trisomy 21)

What is the difference in an individual that is “normal” or an individual that has Down Syndrome?

Turner syndrome

- Only an XO- Short stature,  webbed neck, stocky build

- Ovaries degenerate in late embryonic life, leading to rudimentary

sexual characteristics

Klinefelter syndrome

- Has an XXY- Male, enlarged breast tissue

XYY karyotype:- Tall male with heavy acne

- Some tendency to mental retardation

Triplo-X:- Has an XXX

- Fertile females with normal intelligence

Genetic Disorders

http://learn.genetics.utah.edu/content/disorders/chromosomal/turner/

http://learn.genetics.utah.edu/content/disorders/chromosomal/klinefelter/

http://learn.genetics.utah.edu/content/disorders/chromosomal/down/

C. Diploid and Haploid cells

1. Diploid: cells having two sets of chromosomes

a) Have both chromosomes for each homologous pair

b) Have 2 sex chromosomes

c) All normal human cells except reproductive cells (sperm and egg cells) are diploid

d) Abbreviates as 2n

e) 2n number in humans is 46 (22 pairs of homologous chromosomes and 2 sex chromosomes)

2. Haploid: cells that contain only one set of chromosomes

a) sperm cells and egg cells

b) Have half the number of chromosomes that are present in diploid cells

c) Have only one chromosome of each homologous pair and only one sex chromosome

d) Abbreviated as 1n

3. When a sperm cell (1n) and egg cell (1n) combine to create the first cell of a new organism the new cell will be diploid (2n)

II. Cell Division: process by which cells produce offspring cells

A. Cell division in Prokaryotes

1. Binary fission: division of prokaryotic cell into two offspring cells

2. Three general stagesa) Chromosome makes a copy of itself and attaches

to the inside of the cell membrane

b) Cell grows until it is twice the original size

c) Cell wall forms between the two chromosomes and the cell splits into two new cells

B. Cell Division in Eukaryotes

1. Two types

a) Mitosis: new cells with genetic material that is identical to that of the original cell

b) Meiosis: reduces the chromosome number by half in the new cells

2. Cell cycle: repeating set of events that make up the life of a cell include interphase and cell division

includes

is divided into is divided into

Concept Map

Cell Cycle

M phase (Mitosis)

Interphase

G1 phase S phase ProphaseG2 phase Metaphase TelophaseAnaphase

M phase

G2 phase

S phase

G1 phase

The Cell CycleSection 10-2

3. Interphase: time between cell division

a) G1 phase (gap): cell growth

b) S phase (synthesis): DNA is copied

c) G2 phase: preparation for cell division

4. Cell can exit the cell cycle and enter G0 phase, stop dividing (nervous system cells)

https://www.youtube.com/watch?v=Wy3N5NCZBHQ

C. Control of Cell Division

1. Proteins regulate the progress of cell division at certain checkpoints (traffic signals)

a) green light: go to next stage

b) red light: halt or stop

2. Three checkpoints

a) Cell growth (G1) checkpoint: if cell is healthy and large enough it will go to S phase

b) DNA synthesis (G2) checkpoint: DNA repair enzymes check the results of DNA replication and if everything is correct, it can move to the next step

c) Mitosis checkpoint: signals the cell to exit mitosis and enter G1 phase

3. When control is lost: Cancer

a) Proteins that control cell growth and division are coded for by genes

b) If a mutation occurs in the genes, the proteins may not work properly

c) Cell growth and division may not work correctly

d) Cancer: uncontrolled growth of cells

D. Mitosis: division of the nucleus and is divided into four phases

1. Prophase

a) DNA becomes visible as tight coils

b) Nuclear membrane breaks down

c) Centrosomes appear and move to opposite poles of the cell: two dark spots containing

centrioles

d) Spindle fibers: microtubules that come out of the centrosomes

e) Mitotic spindle: made of spindle fibers and is used to equally divide the chromatids between the two cells

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Prophase

2. Metaphase

a) spindle fibers move the chromosomes to the center of the dividing cell

b) held in place at the center of the cell

3. Anaphase

a) chromatids of each chromosome separate at the centromere

b) move towards opposite poles of the cell

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Metaphase

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Anaphase

4. Telophase

a) spindle fibers break apart

b) chromosomes begin to uncoil and become invisible

c) nuclear envelope forms

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

 Telophase

E. Cytokinesis: cytoplasm of the cell divides

1. Animal cells: cell membrane pinches inward between the dividing cell’s two poles

a) cleavage furrow: area of the cell membrane that pinches in

b) cell is split into two cells

2. Plant cells: cell plate: membrane-bound cell wall that forms in between the dividing cell and forms two cells

Mitosis Video Clip

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Cytokinesis

III. Meiosis A. Meiosis: process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell

1. Gametes: haploid reproductive cells

a) sperm cells and egg cells that are (1n)b) contain 23 chromosomes

2. Sperm and egg cell together form a zygote that contains 46 chromosomes (2n)

B. Stages of Meiosis

1. Cells undergoes G1, S, and G2 phases so there is a duplicate set of chromosomes, so cells need to divide twice

2. First division is called meiosis I and creates 2n cells

3. Second division is called meiosis II and creates 1n cells

C. Meiosis I

1. Prophase I: DNA tightly coiled and spindle fibers appear

a) synapsis: every chromosome lines up next to its homologue

b) tetrad: each pair of homologous chromosomes

c) crossing over: chromatids twist around one another and sometimes a portion may break off and attach to adjacent chromatids ( permits

exchange of genetic material)

d) genetic recombination: new mixture of genetic material

2. Metaphase I: tetrads line up randomly along the midline of the cell

a) spindle fibers from one pole attach to the centromere of one of the homologous chromosomes

b) spindle fibers from the other pole attach to the centromere of the other homologous chromosome

3. Anaphase I: each homologous chromosome (2 chromatids attached by a centromere) moves to an opposite pole

a) independent assortment: random separation of the homologous chromosomes

4. Telophase I: chromosomes reach the opposite ends of the cell and cytokinesis begins

a) two new cells are formed

b) each cell has 46 chromosomes

5. During meiosis I: two new cells produced each containing one chromosome from each homologous pair

a) Each new cell contain two copies of the chromosome because the original cell copied its DNA before meiosis I

Interphase I Prophase I Metaphase I Anaphase I

Cells undergo a round of DNA replication, forming duplicate Chromosomes.

Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Spindle fibers attach to the chromosomes.

The fibers pull the homologous chromosomes toward the opposite ends of the cell.

Section 11-4

Meiosis I

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D. Meiosis II: occurs in each cell formed during meiosis I and the DNA is not copied

1. Prophase II: spindle fibers form and move the chromosomes toward the middle

2. Metaphase II: chromosomes move to the middle and face opposite poles

3. Anaphase II: chromatids separate and move toward opposite poles

4. Telophase II: nuclear membrane forms

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Meiosis II

5. Cytokinesis II: creates 4 new cells each containing half of the original cell’s number of chromosomes

E. Formation of Gametes

1. Meiosis produces haploid reproductive cells (gametes)

2. Meiosis only occurs in reproductive organs (testes and ovaries)

3. Male gametes: sperm cells or spermatozoa

a) spermatids: diploid reproductive cell divides by meiosis to form four haploid cells

b) spermatogenesis: production of sperm when spermatids develops into a mature sperm cell

4. Female gametes: egg cells or ova

a) ovum: diploid reproductive cell divides by meiosis to form one egg cell (uneven dividing of the cell during cytokinesis I and II)

b) polar bodies: three other products that degenerate

c) oogenesis: production of mature egg cells

F. Asexual and Sexual Reproduction

1. Asexual reproduction: production of offspring from one parent

a) does not involve meiosis or union of gametes

b) unicellular organisms: binary fission or mitosis

c) multicellular organisms: budding off of portions of their bodies

d) offspring are genetically identical to parents

2. Sexual reproduction: production of offspring through meiosis and the union of a sperm and egg

a) offspring are genetically different from the parents because genes are combined in new

ways in meiosis

b) offspring contain a unique combinations of their parents genes

c) sexual reproduction enables species to adapt to new conditions