Sexual vs. asexual reproduction

Asexual reproduction occurs by mitosis, it is a careful copying mechanism-meaning all offspring are always genetically identical to the parent

Sexual reproduction occurs by meiosis and brings enormous potential for genetic variability (but the variability will only occur before fertilization

In humans, there are 8,388,608 distinct distributions per gene

DNA Replication DNA plays an important role in protein

synthesis, but also in cell division Cells must be able to divide in order the for

organisms to grow, reproduce and repair itself

DNA is stored in the form of chromatin-long strands of DNA, jumbled up with proteins, that form a disorganized mess of genetic material

When the cell is ready to divide, the chromatin condenses to form chromosomes

Chromosomes Chromosomes are the genetic

information that is passed from one generation to the next

Made up of coiled DNA Each organisms has its own specific

number of chromosomes (humans have 46)

Chromosomes are not usually visible except during cell division

Chromosomes A chromosomes’ identical copy of itself is

called a chromatid Each chromatid is attached at an area

called a centromere (usually located at the center of the chromatid)

Chromosomes

Cell Types Multicellular organisms are made up of

two kinds of cells: reproductive (sex cells) and somatic (body cells)

Reproductive cells have a single set, termed haploid (n)

Somatic cells have two sets, termed diploid (2n)

When the cell divides the chromosomes must be distributed between the new cells

Cell Cycle The cell cycle is the sequence of stages

through which a cell passes between one cell division and the next

There are two main stages: Interphase and Mitosis

Cell Cycle

Interphase Interphase is the phase where the cell is

performing normal cell functions such as protein synthesis and preparing for cellular division

During this phase a series of events (stages) must occur in order for the cell to grow and divide

The stages are G1, S1, G2 (cell growth, DNA replication, and preparation for mitosis via replication of organelles and increasing the amount of cytoplasm)

Interphase Cells remain in interphase for long spans

of their life Once interphase is complete, then the

cell will start to divide First the cell will increase its size and

produce new proteins and organelles Then each chromosome is replicated After the cell has completed interphase,

cellular division will occur

Cellular Division Organisms grow and divide because the cells

divide and more cells are present-not because individual cells grow larger, this is called cellular division

Cellular division relies on DNA because it stores and transmit’s the hereditary (genetic) information from one generation to the next

Cells will only grow to a certain size because if they get too big, they will lose their ability to regulate their energy uses and waste production, also the cell’s DNA will not be able to keep up with the workload to keep the cell functioning

Cell Division Before the cell gets too large, the cell will

divide into two daughter cells All of the cell’s organelles and genetic

information will be duplicated before the cell divides

Each of the new daughter cells will have a complete set of genetic information

Cell division reduces the cell’s volume but not its size

It occurs in two stages: Mitosis and Cytokinesis

Mitosis A type of cell division that generates two daughter

cells with identical components of the mother cell Associated with asexual reproduction-it only

requires one parent cell The division of the nucleus and thus the first stage It is a continuous cycle that most cells will undergo Occurs in most multi-cellular organisms (its called

binary fission in unicellular organisms) It is divided into four phases: Prophase, Metaphase,

Anaphase, and Telophase (PMAT)

Mitosis

Prophase-Prepare It is the longest stage of mitosis Chromosomes thicken and become

visible with a microscope Nuclear membrane disintegrates Centrioles (small cylindrical bodies) move

to opposite ends of the cell Spindle fibers (microtubules) grow from

the centrioles to the chromosomes to help separate them

Prophase-Whitefish

Prophase-Onion

Metaphase-Middle Chromosomes form pairs attached by

centromeres and will align along the middle of the cell

Metaphase-Whitefish

Metaphase-Onion

Anaphase-Apart The centromeres split which causes the

chromosomes to separate back into individual chromatids

The chromatids will move to opposite poles being pulled apart by the spindle fibers

Anaphase-Whitefish

Anaphase-Onion

Telophase-Two A nuclear envelope appears around each

new set of chromosomes The nucleolus reappears

Telophase-Whitefish

Telephase-Onion

Cytokinesis Cyto-cell, kinesis-split Material outside of the nucleus must also

divide Generally beings during telophase This is when the actual cell divides to

form two new cells

Cytokinesis In animals, cytokinesis occurs when the

cell membrane pinches in and divides In plants, a cell plate forms across the

middle of the cell which is then followed by the formation of cell walls on each side

Following cytokinesis, the cell returns to the period of interphase

Cell Growth Cell growth is usually well controlled Most of the time, cells are at different

stages of cellular division throughout the body and divide at different rates

For example, blood cells grow and divide very rapidly whereas brain cells (neurons) do not

There are some instances of uncontrolled cell growth-Cancer

Cancer It is a condition in which cells grow and

reproduce at a rapid rate and do not respond to the usual controls (cyclins) that limit cellular growth

These large masses of cells are called tumors

When tumors form in the body, they can damage the surrounding tissues

If parts of the tumor breaks off into the body, the cancer can spread

http://upload.wikimedia.org/wikipedia/commons/5/56/Macs_killing_cancer_cell.jpg