Chapter 6:  Mitosis and Cellular Reproduction

http://web.as.uky.edu/biology/faculty/palmer/BIO103/Lecture/ch8/08_A03.swf

I.     Chromosomes (pg 119)

A.  Chromosomes are a structure made of DNA on which the genes are located (genetic material takes this form just before and during cell division)

1.    DNA - (deoxyribonucleic acid) - a double sided nucleic acid that stores genetic information (carries the traits passed down from the parents)

2.    Gene - a section of a chromosome containing specific trait information

II.   Chromosome number & structure (pgs 120-121)

A.  The number of chromosomes present varies by species; the number of chromosomes does not determine the complexity of the organism

B.  Homologous Chromosomes - pairs of chromosomes

1.    Homologue - single chromosome in a pair, contains similar size, shape and information as its partner; the information on one homologue comes from the mother the other from the father of the organism

2.    Diploid - cell with both homologues present (pairs of chromosomes, like body cells)

3.    Haploid - cell with only one of each homologue (like gametes or spores)

4.    Zygote - diploid cell formed from the fusion of two haploid gametes

5.    Sex chromosomes - determine the gender of the organism (in humans a pair with 2 X homologues is female, 1 X and 1 Y homologue is male)

III.  Testing chromosome number and structure

A.  Karyotype - (pg 122) - photo of a set of chromosomes arranged in homologous pairs by size; used for predicting potential problems in development of the embryo; abnormalities in chromosome number can lead to developmental problems

1.    Amniocentesis - (p 123) a small amount of amniotic fluid (fluid surrounding the fetus in the uterus) is removed to obtain genetic information from the fetus

2.    Chorionic villi sampling (CVS) - tissue is collected from the extensions of the placenta that connect with the uterus called chorionic villi

B.  Abnormalities in chromosome structure can also lead to developmental problems (pg 124)

1.    Deletion - a piece of the chromosome is missing due to a problem during DNA replication (making a copy)

2.    Duplication - one or more pieces of the chromosome appears twice

3.    Inversion - one or more pieces of the chromosome is switched with an adjoining piece

4.    Translocation - one or more pieces of the chromosome have been moved to an incorrect location

IV.  The Cell Cycle (pg 125)

A.  The cell cycle is a repeating sequence of cellular growth and division

1.    The cell spends 90% of it’s time in Interphase which contains three phases…

a)    First Growth (G₁) phase - cell grows rapidly and carries out routine functions, cells not preparing to divide stay in this phase

b)    Synthesis (S) phase - Cell’s DNA is replicated (copied), at the end of this phase each chromosome consists of two chromatids attached at the centromere

c)     Second Growth (G₂) phase - preparations are made for the nucleus to divide; organelles replicate; spindle fibers are assembled

2.    The last two phases deal directly with cell division

a)    Mitosis - process of cell division in which the nucleus is divided into two identical nuclei

b)    Cytokinesis - process of cell division in which the cytoplasm is divided to form two identical cells

V.     Mitosis (forms two identical diploid cells - pgs 130-1)

A.  Interphase (leads in to mitosis)

1.    Chromosomes are in the form of chromatin at beginning of phase

2.    Chromosomes are copied

3.    Change to form of sister chromatids connected by a centromere after copying

B.  Prophase (beginning of mitosis)

1.    Chromosomes become visible

2.    Nuclear envelope dissolves

3.    Centrioles (or poles) appear and begin to move to opposite ends of the cell

4.    Spindle forms (the spindle is made of the centrioles and microfibers that move the chromosomes during mitosis)

C.  Metaphase

1.    Chromosomes line up along the equator

2.    Chromatids attach to spindle fibers

D.  Anaphase

1.    Centromeres divide (duplicate copies of chromosomes are separated)

2.    Chromatids (now again called chromosomes) move toward opposite sides of the cell with help from the spindle fibers

E.  Telophase

1.    Nuclear envelope forms around each set of chromosomes, forming two new and identical nuclei

2.    Chromosomes uncoil, and appear as chromatin again

3.    Spindle dissolves

4.    Mitosis ends; Cytokinesis begins

F.   Cytokinesis

1.    Cytoplasm is divided into equal halves

2.    In animal cells the cell membrane pinches in toward the center

3.    In plant cells a plate is formed in between the two halves of cytoplasm, from this plate the new cell walls are formed

Mitosis as a part of the cell cycle…

Stages of mitosis in the plant cell…

Mitosis Illustrated…