Chapter 6
Chromosomes
&
Cell Reproduction
1
Prokaryotic (bacterium) Cell
Division
Binary fission is form of asexual
reproduction.
Binary fission produces identical offspring
Binary fission is the process by which
bacteria reproduce
2
Eukaryotic cell
reproduction
Gametes – sex cells
Male – Human sperm cell (23 chromosomes)
Female – Human egg cell (23 chromosomes)
Gametes – haploid cells (n number)
Haploid number is ½ the organism’s body cell
chromosome number.
Human sperm and egg have 23 chromosomes.
Humans the haploid number is 23
The symbol used to designate the haploid
number is n
3
In humans gametes contain 22 autosomes and
1 sex chromosomes
Males – sperm with either an x or y
chromosome
In human males determine the sex of child b/c
males have one x and one y chromosome.
The X and Y chromosome are called the sex
chromosomes
Female : XX :: male : XY
4
Chromosomes/Genes
Chromosomes are made up of DNA, Genes and
Protein.
The DNA in Eukaryotic cells is packaged into structures
called chromosomes.
Chromatids – two exact copies of chromosome
Genes on chromosomes are the units of inheritance
A Gene is a segment of DNA that direct the production of
a specific protein
A gene is a segment of DNA that carries the instructions
for producing a specific trait
There are 1,000’s of genes on a DNA molecule
5
The point at which two chromatids are
attached to each other in a chromosome is
called a centromere
A picture of a cell’s chromosome is called
a Karyotype
Karyotypes can be studied to lean about
the number and structure of a
chromosome in a somatic cell
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Sets of chromosomes
Homologous chromosomes –
chromosomes that are similar to each
other
Somatic chromosomes are called body
cell chromosomes
Somatic cells – contain the diploid or 2n
number of chromosomes
In humans the diploid number is 46
Gametes – sex chromosomes
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Egg cell has 23 chromosomes and a
sperm cell has 23 chromosomes.
A Zygote has 46 chromosomes.
A zygote is a fertilized egg cell.
A diploid cell is one that
– has two homologues of each chromosome
– is designated by the symbol 2n
– Has chromosomes found in pairs
8
Change in chromosome number
Each of an individual’s 46 chromosomes has
thousands of genes.
Sometimes an individual can have an extra copy
or be missing one or more chromosomes.
The failure of replicated chromosomes to
separate is called nondisjunction
A mutation in which a piece of a chromosome is
lost during meiosis is called deletion
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Abnormal syndromes
Down’s syndrome – In humans, this is a
specific condition caused by an extra
chromosome 21
Down’s syndrome is also called trisomy 21
because it is a mutation that results in a
cell having an extra chromosome
People with Down’s syndrome have 47
chromosomes instead of 46
10
Human chromosomes
– Exist in 23 pairs in all cells but gametes
– Each contain thousands of genes
– Form right before cells divide
In order to fit within a cell , DNA becomes more
compact by wrapping tightly around
associated proteins.
The shape of a bacterium’s chromosome is
circular
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1. How many chromosomes are in the
body cell of an organism with the haploid
number of 8? ____
2. Diploid number is 46 then what is the
number of chromosomes found is a
human ovum ? ___
3. Diploid : somatic :: haploid : ______
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1. 16
If the haploid or sex chromosome number was 8 then
Diploid (2n) would be 2(8)=16
2. 23
If the diploid number was 46 then the haploid number
would be ½ which is 46/2 = 23
3. Gamete
Diploid cell and somatic cell are the same.
Therefore what word means the same as haploid?
Gamete is the same as haploid
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The Cell Cycle
Section 2
CELL CYCLE – sequence of events that occurs
in a cell from one mitotic division to the next.
Normal cell growth and cell division are
stimulated by PROTEINS
The information needed by a cell to direct its
activities and to determine its characteristics is
contained in molecules of DNA
After cell division, each new cell will contain the
same genetic information as the original cell.
Asexual reproduction can occur by mitosis
14
Cell Cycle
Cell cycle (G1 – S – G2 – M – C)
– Interphase
G1 – first growth phase
S phase – Synthesis phase
G2 – 2nd growth phase
– Mitosis
Prophase
Metaphase
Anaphase
Telophase
– Cytokinesis
Cytoplasm divides
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Interphase
Interphase is the phase that the cell cycle
occupies most of the cell’s life
Cell spends 90% of its time in this phase
The first three phases of the cell cycle are
collectively known as Interphase
16
Section 3
Mitosis – is a process by which the nucleus is divides
into two nuclei
Mitosis – is a process by which a cell’s nucleus
divides
Spindles – structures that will move chromosomes
during cell division
A spindle fiber is a specialized from of microtubule
Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase
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Prophase
Prophase – 1st stage of mitosis
- Chromosomes coil up into short, fat rods
- Chromosomes coil up and become visible
- The nuclear membrane dissolves
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Metaphase/Anaphase/Telophase
Metaphase - The arrangement of all
chromosomes along the equator of the cell
Anaphase –
– The stage in which the centromeres divide.
– Chromosomes move toward opposite poles
Telophase– Spindle dissolves
– Nuclear membrane forms around each set of new
chromosomes
– Chromosomes uncoil
– Cell membrane begins to pinch inward
– In plant cells = a cell wall begins to form
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Cytokinesis
Cytokinesis – last stage of the cell cycle
Mitosis ends and Cytokinesis begins
Cytokinesis - Cytoplasm of the cell is
divided into half, and the cell
membrane grows to enclose each cell.
After mitosis and cytokinesis, each new
cell has a complete set of the parent’s
chromosomes
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Plant and Animal cells both undergo cell division
Plant and animal cells have different strategies
for cytokinesis
Animal cell - cell division
– No cell wall
– Cell membranes form
Plant cell – cell division
– Cell membrane forms
– Cell Wall Forms
Cytokinesis in plant cells involves the formation
of a cell plate
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CANCER
Cancer is a disease characterized by
uncontrolled cell growth
Normal cells become cancerous when
– Regulation of cell growth and division is
lost
– Cell’s do not respond normally to control
mechanisms
– Cells continue to divide without passing
through G1
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Pg 130
Be able to place sketches in correct order
for mitosis
Prophase
Metaphase
Anaphase
Telophase
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