Why do cells divide rather than grow bigger?
– Have you ever been in a traffic jam in a small town?
– Where are major traffic jams found?
• As a city’s population grows, more people are moving in an out which causes traffic
• Cells are like cities
– The bigger they are, the more food, water, and waste that must move in and out to keep the cell alive.

Why do cells divide rather than grow bigger?
• To prevent traffic jams, they will divide
• Cells divide for 4 major reasons:
1. Prevent the cell from becoming too big
(prevent traffic jam)
2. To heal injuries
3. To allow the organism to grow
(up)
4. To reproduce
(new individuals)

Before we get started with the cell cycle….
Lets talk about chromosomes
Chromosome : DNA-containing structure that carries genetic material from one generation to another.

What happens during the cell cycle?
Cell Cycle Process of cellular reproduction, occurring in the main stages
1. Interphase (growth)
2. Mitosis (nuclear division)
3. Cytokinesis (cytoplasm division)

What occurs during Interphase
(the 1 st step in cell cycle)
• There are 3 stages during interphase:
1 st Grows
2 nd Duplicates DNA
3 rd Prepares to divide
46
Chromosomes 92
Chromosomes

Which of the following is NOT a reason cells divide?
a. To heal injuries b. To allow the organism to grow c. To reproduce d. To maintain homeostasis

What will happen if the cell continued to grow rather than divide?
a.
The organism would get too big b.
Food & wastes would not be able to move in & out as easily c.
The surface area would increase and allow more materials into and out of the cell d.
Nothing would happen

What are the 3 stages of the cell cycle?
a. Prophase, Metaphase, & Anaphase b. Mitosis, Telophase, & Cytokinesis c. Interphase, Metaphase, & Prophase d. Interphase, Mitosis, & Cytokinesis

Which of the following is NOT a stage during interphase?
a. Growth (G1) b. DNA replicates (S) c. Prepares to divide (G2) d. Mitosis (M)

Mitosis
: 2 nd main stage of the cell cycle during which the cell’s replicated DNA divides and 2 genetically identical diploid daughter cells are produced.

What occurs during mitosis?
(the 2 nd step in cell cycle)
• There are 4 stages during mitosis:
1 st Prophase (pro = 1 st )
2 nd Metaphase
3 rd Anaphase
4 th Telophase (telo = end)

What occurs during mitosis?
(the 2 nd step in cell cycle)
• There are 4 stages during mitosis:
1 st Prophase (pro = 1 st )
Nucleus disappears
Centrioles separate

What occurs during mitosis?
(the 2 nd step in cell cycle)
• There are 4 stages during mitosis:
2 nd Metaphase Chromosomes line up in the middle

What occurs during mitosis?
(the 2 nd step in cell cycle)
• There are 4 stages during mitosis:
3 rd Anaphase
Chromosomes move apart

What occurs during mitosis?
(the 2 nd step in cell cycle)
• There are 4 stages during mitosis:
4 th Telophase (telo = end)
Nucleus reappears
Cytoplasm starts to separate

What occurs during cytokinesis?
(the 3 rd step (LAST) in cell cycle)
•
Cytokinesis : The last stage of the cell cycle, during which the cell’s cytoplasm divides, creating a new cell.
Daughter Cells

a. 4 genetically identical cells b. 2 genetically identical cells c. 4 genetically different cells d. 2 genetically different cells

What are the 4 stages of mitosis in order?
a. Interphase, prophase, metaphase, anaphase b. Interphase, prophase, metaphase, telophase c. Prophase, metaphase, telophase, cytokinesis d. Prophase, metaphase, anaphase, telophase

This is the last phase of the cell cycle where the cell’s cytoplasm divides to create 2 daughter cells: a. Cytokinesis b. Interphase c. Telophase d. Metaphase

What is the difference between gametes & body cells?
Gametes
– A haploid sex cell, formed during meiosis, that can combine with another haploid sex cell and produce a diploid fertilized egg.
Sperm & Egg are gametes !
How many chromosomes are in human gametes?
23

What is the difference between gametes & body cells?
has mean that it is more
EXCEPT
Heart cells
GAMETES!
Skin cells Muscle cells
Blood cells Lung cells
Kidney cells
No …example:
Nerve cells
How many chromosomes do we have in each of our body cells
(not sex cells)?
Humans have
46 in our body cells

Body cells reproduce using
.
Start with 1 diploid
Notice that they are IDENTICAL!
End with 2 diploid

Diploid
–
Having two copies of each chromosomes (2 n )

Haploid
–
Cell with half the number of chromosomes ( n )
23
23
23
23
hap
Skunks have 25 loid
(in sex cells)
Remember: Humans have 46 (in body cells)
HALF

Sperm and eggs are: a. gametes b. somatic cells c. body cells d. all of the above

How many chromosomes are in human gametes?
a. 36 b. 23 c. 20 d. 15

Which of the following is an example of a haploid cell?
a. brain cell b. skin cell c. heart cell d. sperm cell

Mitosis results in: a. 2 diploid cells b. 2 haploid cells c. 4 diploid cells d. 4 haploid cells

Starts with 1 diploid
Notice that they are
NOT IDENTICAL
Ends with 4 DIFFERENT haploid

Meiosis
: Reduction division process, occurring only in reproductive cells, in which 1 diploid (2 n ) cells produce
4 haploid ( n ) cells that are NOT genetically identical.
Creates SPERM inside the testes of males
Creates EGGS inside the ovaries of females

There are 2 stages during Meiosis:
Meiosis I & Meiosis II
Meiosis I is exactly like mitosis EXCEPT that
Crossing-over occurs during prophase I

Crossing-over : Exchange of chromosomal segments between a pair of homologous chromosomes during prophase I of meiosis
Meiosis I
Meiosis II

Why is crossing-over so important?
(cuz it is)
• It creates genetic variation!
• Even though you look similar to your siblings
(if same parents), there will never be another person exactly like you because of crossing-over…your parents could have a million kids, and not one of them will look exactly like you!
(except for identical twins, but even they have some differences)
Genetic variation allows some individuals to:
* Run faster than you * “Look better” than you
* Fix things better than you
* Solve math problems better than you
* Train animals better than you
* Fly airplanes better than you
* Swim better than you
* Paint better than you
* Sing better than you
* Farm better than you
* Dance better than you
* Jump better than you

Crossing-over occurs between homologous chromosomes .
The same crossing-over patterns do
Homologous Chromosomes means that they contain the SAME
Being genetically unique called “recombination”…this creates genetic diversity !
not occur…they create all different
SAME unique .
Genetic diversity allows some
- And your dad’s code could be for brown continue as their environment changes…even if others can’t survive.

Hypothetical….lets say you are a duck… cuz that is what the ladyz are look’n for

Hypothetical…lets say you are a caveman
Which of these would be LESS likely to survive?
Because all these cave people have genetic diversity, but one lacks an important trait (ability to build tools), he will not survive his environment… but the others will !

Next is Meiosis II ….
* The division process happens again…BUT
Meiosis I
The DNA does NOT copy before dividing
&
Meiosis II
No crossing-over
Results in 4 haploid cells that are NOT identical

Which of the following cells are formed during meiosis?
a. skin cells b. liver cells c. egg cells d. kidney cells

Which of the following cells are formed during mitosis?
a. skin cells b. sperm cells c. egg cells d. all of the above

Meiosis results in: a. 2 identical haploid cells b. 4 identical haploid cells c. 4 different haploid cells d. 2 different haploid cells

This allows some individuals of the same species to continue as their environment change even if others can’t survive a. identical twins b. cloning c. genetic variation d. biodiversity

The exchange of chromosomal segments during meiosis is called: a. interphase b. crossing-over c. transcription d. exchanging-over

Which of the following allows for genetic diversity?
a. meiosis b. mitosis c. homeostasis d. all of the above

Non-disjunction : Cell division in which the sister chromatids do NOT separate correctly, resulting in gametes with an abnormal number of chromosomes.
This is how Down Syndrome
These are correct!
Notice there are
No problem
NO chromosomes in these cells!
47 non-disjunction occurred chromosomes instead of ____.
here too!
46

Page 34 in Comp Book
Compare & Contrast Mitosis & Meiosis
Mitosis Meiosis
* Occurs in body cells
* Divides once
* Creates 2 cells
* Are genetically identical
Both * Occurs in gametes cells
* Creation of new cells
* Divides twice (meiosis 1 & II
* Creates 4 cells
* DNA replicates once
* Are NOT genetically identical
* Increases genetic diversity

This results in gametes with abnormal numbers of chromosomes: a. meiosis b. mitosis c. non-disjunction d. crossing-over

This is an example of nondisjunction: a. Color blindness b. Down Syndrome c. Cystic fibrosis d. Sickle cell anemia

Many Bacteria & protozoans do not need a partner to reproduce. Are they reproducing using mitosis?
Answer: NO ...
They are using Binary Fission
Binary Fission – Asexual form of reproduction used by some prokaryotes in which a cell divides into two genetically identical cells. (creates a new individual)
SIMILAR/LIKE “cloning” themselves
1 bacterium could become 1,000,000,000
(billion) in 10 hours!

What are the advantages & disadvantages to being asexual & sexual?
Asexual Reproduction
Advantages Disadvantages
Can reproduce without a partner…
They don’t have to find a mate/partner.
Able to reproduce quickly. The greater the number of offspring, the better the survival rate of the population.
No genetic variation…They are clones.
Its putting all your eggs in one basket.
If a something kills the parent, it
WILL kill ALL the offspring too.
Easily becomes extinct with little change to environment.
Quick reproduction is also a disadvantage because too many individuals will be competing with each other for food & space

What are the advantages & disadvantages to being asexual & sexual?
Sexual Reproduction
Advantages Disadvantages
Genetic diversity!
Has the ability to create endless recombination of genes (crossing-over) coming from 2 parents, all individuals are different in some way.
The species is more able to adapt to environmental changes
Must find a partner. Very difficult if the population is low and spread out.
Difficult to recover if the species is endangered.
Slow reproduction….takes time…
Slow population growth

Prokaryotes reproduce using: a. meiosis b. mitosis c. binary fission d. binary fusion

Which of the following is an advantage of asexual reproduction a. genetic diversity b. the ability to reproduce quickly c. the ability to adapt to new habitats d. slow reproduction

Which of the following is an advantage of sexual reproduction a. genetic diversity b. the ability to reproduce quickly c. the ability to reproduce many offspring d. do not have to find a sexual partner