Friday March 7th, 2008

Section 3-

Chapter 12 - Cellular Reproduction

Function of cell division -

Unicellular organisms - reproduction

multicellular - growth & tissue repair

2 Types of Cell Division:

1.) Asexual

• daughter cells are identical to the mother cell (clones).
• All organisms do this
• Prokaryotes -- Binary Fission
• Eukaryotes -- Mitosis

2.) Sexual

• daughter cells are notidentical copies of the mother cell & not identical to each other.
• found only in eukaryotes
• meiosis.

most important part of cell division is the accurate replication and separation of genetic material to the daughter cells.

Asexual - all this can happen in 20 minutes -- how sick you can get in such a short time.

Cell division in bacteria - binary fission

• the single circular chromosome is replicated.
• each DNA copy is attached to the cell membrane at opposite ends of the cell.
• Cell elongates - separates the 2 DNA molecules
• Cell splits in two (new cell wall is formed between the two) 

Cell division in eukaryotes - meisosis

• Eukaryotes have multiple chromosomes.    (Chomo -"colored"  Somes -"bodies")

• Nucleus - chromosomes decondensed -

  condensed chromosomes are -->going into cell division

  at this time, eah chromosome can be distinguished as separate things.

• Each chromosome is made up of one long, linear DNA molecule -millions of base pairs long (bp = base pairs)

Chromosome structure:

Chr  - chromosomes- Arms make copies of each other to form Sister Chromatids.

1 Chromosome = 1 Chromatids when its just the one

When its split - 1 chromosome still, but two chromatids.

Chr in Eukaryotes come in sets (Ploidy)

Ex. Humans = 1 set of chromosomes = 23 chromosomes

      Tomatoes = 12 chomosomes/set ; Corns = 10 chromosomes / set.

Cells in the body = somatic cells. -- have 2 sets of chomosomes. So 2 sets of 23 =  46 chromosomes.

That 2 sets = Diploid  (di = 2, ploid = sets)

Wheat has 6 sets of Chromosomes.