NOTES-

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