Friday - March 14th, 2008

 

ACK! Missed on Wednesday -- Need to Borrow Notes!

Define the following & know the Stages of Mitosis - Innerphase Prophase PrometaphaseMetaphase Telophase Anophase Cytokinesis.

Cancer

Kareotype

Genome

Cell cycle

 

 

 

 

 

 

Reproduction:

 

1.)Asexual - like a hydra (plant) -- genetically identical

2.) Sexual - meiosis - eukaryotic -- Daughter

cells are genetically different from each

other, & from the mother cell.

 

a.) different - # of sets of chromosomes

parent - diploid - 2 sets.

daughter cells - haploid - one set

= germ cells = gametes.

 

sets = n    2n = diploid

                1n = haploid

 

b.) different gene combinations

 

 

Homologous chomsomes  -- are chromosomes of the same

size and shape that carry genes for the same traits (characters).

Life cycle - Sexual:

Meiosis -

1.) only occurs in special cell types.

2.) Chromosomes replicated.

3.) 2 divisions with no intervening DNA replication = meiosis I & meiosis II.

4.) Meiosis I - where the unique events occur.

 

a.) Prophase 1

• 1.)Homologous chromosome pairs = synapse -- side by side and tightly along their complete length.

• 2.) Homologous chromosomes crossover: exchange DNA segments.

   

b.) Anaphase I

• Homologous chromosomes separate
• Reduction division = 2n --> 1n + 1n.

 

c.) End of Meiosis one.

• 1.) 2 cells -- each is haploid (1n).

• 2.) each chromosome is composed of 2 chomatids.

 

5.) Meiosis II - just like mitotic division of a haploid cell (no DNA synthesis).

Sister chromatids separate.

Result = 4 cells, each is haploid,

and each chromosome is composed of one chromatid

 

Overall meiosis produces 4 haploid cells that will become gametes

(from an original diploid mother cell) Each of these haploid cells is genetically

different from the others.

 

The crossovers spots are chiasma, chiasmata plural = just another word for crossover process??

 

Differences between the Mitosis and meiosis

Mitosis	Meiosis
Most common form of cell replication - used for growth & tissue repair.	Limited to only specific types and used only to make gametes
Mitosis involves one cell division - results in 2 daughter cells	2 cell divisions -but only one round of DNA replication to give 4 cells
Daughter cells have the same # of chromosomes as the mother cell. 2n = 2n,2n	The daughter cells have only half the # of chromosomes of the mother cell. 2n = 1n, 1n, 1n, 1n
Genetically identical daughter cells	Daughter cells are not genetically identical
	meiosis creates genetic variation

Meiosis is part of sexual reproduction.

-offspring are highly variable geneticaly.

-better chances of survival in a changing environment.

 

Sources of genetic variation in sexual reproduction:

1. Crossing over : During Meiosis I, homologous chromosomes pair and sements of DNA are exchanged between homologous chromosomes.

2. Independent assortment: In meiosis I, each pair of homologous chromosomes separates without regard to how the other pairs are separating. In humans, there are 2^23 combinations. ( more than 8 million combinations before considering crossovers.) Infinite

   number of combinations possible.

3. Random fertilization.