Unit 1:

“Reproduction”

Part 1:

Asexual vs. Sexual Reproduction

I. Asexual Reproduction

Form of reproduction where only one parent is involved.

Also reproduction without the fusion of gametes (sperm and egg)

Primary form of reproduction for single-celled organisms such the bacteria, and protists. Many plants, fungi, and even some animals reproduce asexually as well.

II. Types of Asexual Reproduction:

1. Binary Fission: used by bacteria

2. Fragmentation/Regeneration: used by organisms such as Fungi, Moss, Sea Stars, Planaria

3. Budding: used by organisms such as yeast and hydra

Binary Fission

Asexual

Cell splits and replicated DNA goes with each part

Prokaryotes, Bacteria

+ Fast and easy

- Everybody has the same DNA

Fragmentation/ regeneration

Asexual

Body of parent breaks and produces offspring

Fungi, moss, sea stars, planarian

+ Easy

- Parent broken, same DNA

Fragmentation/ regeneration

Moss

Budding

Asexual

Offspring grows out of parent

Yeast, hydras

+ Fast, somewhat easy

- Same DNA

III. Asexual Advantages

1. Need one individual to reproduce; can conserve energy

2. No genetic change “good” if environment is stable

3. All individuals are producing offspring

4. More efficient passing genes, “faster”

 

IV. Asexual Disadvantages

1. No recombination of genes 

2. An asexual population tends to be genetically static

Mutant alleles Beneficial alleles

V. Sexual Reproduction:

A. Processes that pass a combination of genetic material to offspring, resulting in diversity.

B. The main two processes are: meiosis (involving the halving of the number

of chromosomes) fertilization (involving the fusion of two

gametes and the restoration of the original number of chromosomes.

VI. Advantages of Sexual Reproduction

1. Offspring are genetically unique from:• A. Crossing over• B. Independent assortment   • C. Random fusion of gametes

2. Favorable when the environment is not stable3. Slower rate of reproduction but faster

adaptation/evolution4. Lower extinction rates5. Fast removal of bad mutations or can put two

beneficial mutations together6. Better adaptation to host-parasite arms race.7. Offspring are dispersed widely to end

up in different places from their parents  

VII. Disadvantages of Sexual Reproduction

1. Need two parents “must expend energy” to find, identify (court), and copulate with mate

2. Genetic recombination is counter productive if conditions are stable   

Part 2

Mitosis

Why Cell Division?

A. Necessary for the growth of organisms.

B. Necessary for every cell in organism to have the genetic instructions to survive.

C. Genetic instructions passed through DNA in chromosomes.

The Cell Cycle:

A. Cell division occurs during the cell cycle

B. It is the repeating set of events that make up the life cycle of a cell.

C. Divided into two phases:1. Interphase: time between cell divisions2. Cell Division: consists of two stages

a. Mitosis: division of nucleus.b. Cytokinesis: division of cytoplasm of

the cell.

Stages of Interphase:

1. G1 Phase: cell growth.

2. S Phase: DNA replication.

3. G2 Phase: growth and prep

***G0 Phase: used by some cells to exit cell cycle

Stages of Cell Division in Eukaryotes:

1) Prophase

2) Metaphase

3) Anaphase

4) Telophase

Events of Prophase:

1) DNA coils into chromosomes.

2) Nucleolus disappears; nuclear membrane disappear.

3) Centrioles appear and migrate to opposite sides of cell.

4) Spindle fibers form

Events of Metaphase:

1) Chromosomes migrate to the center of the dividing cell. Held in place by the spindle fibers.

Events of Anaphase:

1) Sister Chromatids pulled apart by fibers.

2) Chromatids pulled toward centrioles.

3) Now have individual chromosomes at opposite ends of cell.

Events of Telophase and Cytokinesis:

1) Spindle fibers disassemble.

2) Nuclear membranes form around chromosomes at each end.

3) Chromosomes uncoil.

4) Nucleolus forms in each new nucleus.

5) CYTOKINESIS occurs.

6) Cell membrane pinches inward (forms cleavage furrow) until two cells form.

Stages of Cell Division in Prokaryotes:

A. Process called Binary Fission.1. Chromosome makes copy of itself.

2. Cell grows until it is twice its normal size.

3. Cell wall forms between two chromosomes, and splits into two new cells.

Multicellular Organization:

Levels of Organization:

1) Tissue: groups of CELLS carrying out specific function (EX. epithelial).

2) Organ: groups of TISSUES performing specific function (EX. stomach).

3) Organ system: group of ORGANS performing specific function (EX. digestive system).

*** SEE FIGURE 4-18 (p. 88)

Week 2:

Meiosis

I. Meiosis:

A. Meiosis is a reduction division, which means dividing cells begin as diploid (2n) and divide by mitosis into four haploid (1n) cells.

B. Meiosis involves two mitosis divisions.

C. The first cell division is called Meiosis I and the second cell division is called Meiosis II.

D. Cells preparing for meiosis first undergo G1, S, and G2 phases of Interphase.

II. Steps of Meiosis I:

1) Prophase I: Same as prophase in mitosis, but Synapsis (the pairing of tetrads- does not occur in mitosis) and CROSSING-OVER occurs (does not occur in mitosis).

2) Metaphase I: Tetrads line up randomly along the equator of the cell.

3) Anaphase I: Each homologous chromosome moves to opposite pole of cell (called Independent Assortment).

4) Telophase I: Chromosomes reach opposite sides of cell, cytokinesis begin. Result is two new cells that contain a haploid number of chromosomes.

III. Steps of Meiosis II:

1) Prophase II: Spindle fibers form in each cell from Meiosis I.

2) Metaphase II: Chromosomes move to the equator of the daughter cells.

3) Anaphase II: Chromatids separate and move towards the poles of the cell.

4) Telophase II: Nuclear membrane and nucleolus reappears in each of four new cells; each cell contains half of the original cell’s number of chromosomes.