Post on 12-Mar-2020
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CHAPTER 6
CHROMOSOMES AND CELL REPRODUCTION
Section I Chromosomes
Formation of New Cells by Cell
Division
.
• New cells are formed when old cells
divide.
• 1. Cell division is the same as cell
reproduction.
• 2. The type of cell division differs
depending on the organism.
Prokaryotic cells, like Bacteria
reproduce by binary fission.
• Binary fission: asexual/ a single parent
passes exact copies of its DNA to its
offspring
• 1st stage: DNA is copied
• 2nd stage: Cell divides
Eukaryotic cells reproduce by another
type of cell division-
MITOSIS • 1st stage: DNA is copied
• chromatids: 2 exact copies of DNA that make up a chromosome
• centromere: point of attachment
of 2 chromatids
• 2nd Stage: DNA and protein coil into chromosomes
• Draw and Label a chromosome:
• The chromatids separate during cell
division and are each placed into a new
cell. This ensures that each cell has the
same genetic information as the
original cell.
• When a cell divides: the DNA is copied
1st and then distributed. Each cell ends
up with a complete set of the DNA.
Gamete cells- which are sperm and
egg are created through another type
of cell division-MEIOSIS
Egg cell surrounded by
sperm cells.
II. Chromosome Number and
Structure
• Humans have 46 chromosomes
(23 Pairs) in somatic cells.
• Somatic cells: All body cells
(except sex cells)
• Gametes: sex cells (sperm and
eggs)
• Chromosomes differ in size,
shape and set of genes.
Sets of Chromosomes
• Homologous chromosomes are
those that are paired together and
are similar in size, shape and
genetic content.
• 46 chromosomes = 2 sets of 23
Diploid- cell contains 2 sets of chromosomes
Haploid- cell contains 1 set of chromosomes
The fusion of 2 haploid cells forms a diploid
zygote.
Zygote-fertilized egg cell
B. Sex Chromosomes
• Out of 23 pairs of chromosomes- 22
pairs are autosomes; 1 pair are sex
chromosomes.
• Sex chromosomes are the X and Y.
• Male Sperm determines the sex of a
child.
• XX = Female XY = Male
C. Change in Chromosome Number • There are 1000’s of genes on each of our
chromosomes.
• The presence of all 46 chromosomes is
essential for normal development and
function.
• Trisomy- having an extra copy of a
chromosome
• Example: Trisomy 21- Down’s Syndrome
• Cause of Trisomy is NONDISJUNCTION.
• This is when the chromosomes don’t separate
and one gamete ends up with 2 chromosomes.
Mikey has Down’s Syndrome. He has an extra chromosome. Instead of having a
pair of # 21 chromosomes, he as 3 copies of it.
Karyotype:
Normal vs Down’s Syndrome
D. Change in Chromosome
Structure- MUTATIONS • Types of Mutations:
1. Deletion- piece of chromosome breaks off
2. Duplication- extra chromosome fragment
attaches; 2 copies of certain genes
3. Inversion- chromosome attaches in
reverse order
4. Translocation – chromosome piece
attaches to a nonhomologous chromosome
See p 124 Draw these Chromosomal
Mutations
Section II- The Cell Cycle
A. Cell cycle-Cellular growth and division
• 90% of the time is spent in Interphase.
(preparation to divide)
• The cell will enter the last 2 phases of
the cell cycle only if it is about to divide.
5 Phases of the Cell Cycle
The 1st 3 stages are part of Interphase.
• 1. 1st Growth (G1)-Grows rapidly (nerve
cells stay in this stage)
• 2. Synthesis- DNA is copied; each
chromosome is copied
• 3. 2nd Growth (G2)- Growth; prep for
division; microtubules are assembled
• 4. Mitosis- nucleus divides into 2 nuclei
(2 cells) that are identical
• 5. Cytokinesis- cytoplasm divides
• Mitosis and cytokinesis
produce new cells that are
identical to the original cells
and allow organisms to grow,
replace damaged tissue, and
in some organisms,
reproduce.****All cells –
EXCEPT gametes reproduce
by Mitosis!!!!***********
B. How do cells “know” when to divide?
“Red light- Green light”
• The cell cycle in eukaryotes is controlled by many proteins.
• 1.Cell growth check point(G1): makes decision whether cell will divide
• 2. DNA synthesis checkpoint (G2): protein triggers mitosis and cell begins many processes needed to proceed into mitosis
• 3. Mitosis checkpoint: triggers the exit from mitosis; It signals the beginning of G1.
• Uncontrolled growth of cells
• It is essentially a disorder of cell division.
• Cancer cells do not respond normally to the
body’s control mechanisms
• Some Mutations cause cancer by over-producing
growth-promoting molecules, thus speeding up
the cell cycle or by inactivating the control
proteins that normally act to slow or stop the
cell cycle.
CANCER-
Section III Mitosis and
Cytokinesis
• 4 stages of Mitosis:
1. Prophase
2.Metaphase
3. Anaphase
4. Telophase
Prophase: • Chromosomes become visible, the
nuclear envelope dissolves and the spindle forms.
• What makes up the spindles? It is made up of centrioles & individual microtubule fibers; they are involved in moving the chromosomes.
Metaphase • Chromosomes line up in the Middle
(middle phase)
Anaphase • Centromeres divide, chromatids move
toward opposite poles.
Telophase
• Nuclear envelope reforms at each pole,
chromosomes uncoil , spindle divides.
• Mitosis is complete and cytokinesis begins.
Cytokinesis
• Cytoplasm divides in half, and the
membrane grows to enclose each cell, 2
separate cells are formed.
A Difference in Plant Cells
• A cell plate forms across the middle
of the plant cell. A new cell wall
forms on both sides of the cell
plate. See Figure 11 on page 132.
Put the following in the correct
order
• Put the following pictures in the correct order as they occur during mitosis:
• Answer: c,b,d,a