Standard 6Emily and Cammie

Describe the roles of mitotic and meiotic

divisions during reproduction, growth,

and repair of cells.

What is Mitosis?• Mitosis occurs when a eukaryotic cell

reproduces. It divides it’s chromosomes, which are in the nucleus, into identical sets of daughter nuclei. Mitosis always produces diploid cells, which have two sets of chromosomes.

Stages of Mitosis• Interphase

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

Interphase• The cell

doubles the chromosomes through DNA replication.

Prophase• All chromosomes

and corresponding homologous chromosomes pair to form a tetrad.

Metaphase• All the

tetrads line up and attach to the spindle fibers.

Anaphase• The spindle

fibers pull the daughter chromosomes to opposite sides of the cell.

Telophase and Cytokinesis• The

chromosomes reach the opposite sides and nuclear membranes form. The cell divides into two cells.

What is Meiosis?

In meiosis, the cells made in mitosis go through a second division. The cell’s chromosomes, which are it’s genetic information, are divided into two sex cells (sperm and egg). Later, the sex cells can combine

and create an offspring with the full amount of chromosomes.

Phases of Meiosis The first stage of

meiosis is the same as mitosis. This stage is called meiosis I. The second stage of meiosis (meiosis II) is when reduction and division takes place.

The First Stage of Meiosis

The stages of meiosis I and mitosis are identical. They are called:

• Interphase I• Prophase I• Metaphase I• Anaphase I• Telophase I• Cytokinesis

Prophase IIProphase II and prophase I are almost identical,

except prophase II has half the number of chromosomes in each cell.

In this phase, spindle fibers begin to develop.

Metaphase II The chromosomes line up and the

sister chromatids face opposite sides of the cell.

Anaphase IIDuring anaphase II, the paired

chromatids separate and go to the opposite sides of the cell.

Telophase II and Cytokinesis

During telophase II and cytokinesis, each set of chromosomes has a nuclear envelope form around it, which results in four haploid cells.

Meiosis and Variation In meiosis, crossing over (when

chromosomes exchange pieces of themselves with each other,

so each cells has its own unique gene combination) and independent assortment(when

chromosomes are sorted independently so that each

gamete, egg or sperm, obtains one pair of chromosomes) lead

to genetic variation, meaning your genetics are different from

your parents.

Meiosis and Reproduction During sexual reproduction,

two haploid sex cells (which are known as gametes) form

a new organism. After fertilization occurs, a zygote, or a diploid cell (which has

two sets of chromosomes) is formed. Meiosis’s role is to change a diploid cell to a haploid gamete, so the

genetic information of the offspring differs from the

parent’s.

Mitosis and Cell RepairCertain body cells are

needed to be regenerated occasionally because of

damage. When cells repair, for example your

skin, they undergo mitosis to create more skin cells

to heal the wound.

Mitosis and GrowthEvery time a single cell duplicates in mitosis it

causes the organism to grow because it has

more cells. Once that cell duplicates, it and it’s duplicate continue to make more identical

cells, increasing the cell count.

QUESTION TIME!

Meiosis and mitosis are two different reproductive

processes. What happens ONLY during meiosis?

A. Crossing over occursB. Replication of organelles

C. Disappearance of the nucleolusD. Complete breakdown of the nuclear membrane

Question 1

Answer 1

ACrossing

over occursCrossing over leads to genetic variation.

Question 2Which statement is correct?

A. Meiosis is a way to reproduce, but mitosis is not.

B. Meiosis is a way to create diversity, but mitosis is not.

C. During mitosis, chromosomes are copied, but during meiosis chromosomes double.

D. During mitosis, chromosomes numbers double, but during meiosis chromosome numbers remain

constant.

Answer 2

BMeiosis is a way to create diversity, but mitosis

is not.In meiosis half the genetic content from the mom and

half from the dad are given to the offspring so it produces unique characteristics, but in mitosis the cell

just splits so there is no diversity.

Question 3Which process requires meiosis?

A. Egg production

B. Bacterial fission

C. Flatworm regeneration

D. Vegetative propagation

Answer 3

AEgg production

Because egg production is done sexually

Question 4Which statements about cell division are CORRECT?

1. Mitosis leads to variation in species.

2. Meiosis leads to variation in a species.

3. Mitosis produces haploid cells used in reproduction.

4. Meiosis produces haploid cells used in reproduction

A. Statements 1 and 3

B. Statements 1 and 4

C. Statements 2 and 3

D.Statements 2 and 4

Answer 4

DStatements 2 and 4

Meiosis leads to variation in a species and meiosis produces haploid cells used in reproduction.

Because haploid cells are used in meiosis not mitosis

Question 5 Red blood cells carry oxygen to the body

during respiration and typically have a lifespan of four months. What is the role of mitosis during respiration?

A. Allows cells to absorb oxygen from the airB. Causes cells to release oxygen to the bodyC. Helps replace cells that are destroyed or damagedD. Produces molecules needed to maintain cell

structures

Answer 5

CHelps replace cells that are destroyed

or damagedIt does this to maintain red blood cells.

Question 6Which of the following is a true statement

about asexual reproduction?

A. Only one organism is needed

B. A mutation needs to occur

C. Meiosis is necessary

D. DNA is not required

Answer 6

AOnly one organism is needed

Because in asexual reproduction, a single cell splits.

Question 7Which reproductive process is

MOST like the regenerative process of skin cells?

A. Yeast creating buds

B. Ovaries forming eggs

C. Ferns producing spores

D. Muscles growing in size

Answer 7

DMuscles growing in size

The cells grow because the are duplicated.

Question 8Which cell process is represented by process 1 of reproduction?

A. Meiosis C. Respiration

B. Mitosis D. Fertilization

2n

2n

2n

n

n

n

n

Process 1

Process 2

Answer 8

BMitosis

Because it is asexually divided.

Question 9 Study the sequence below. Which cellular process

missing from this sequence produces cells having a chromosome number 2n?

2n

Skin cellsundergo

? Skin cellsto form

Having chromosome number

2n

A. Meiosis C. Respiration

B. Mitosis D. Fertilization

Answer 9

BMitosis

Because they have the same number of chromosomes.

Question 10What is the third stage of Mitosis?

A. Anaphase

B. Prophase

C. Telophase

D. Metaphase

Answer 10

DMetaphase

Anaphase is 4th, prophase is 2nd, and telophase is 5th.

Question 11Which is produced by meiosis?

A.4 Haploid cells

B.2 Diploid cells

C.2 Haploid cells

D.4 Diploid cells

Answer 11

AFour haploid cells

In the first stage of meiosis (mitosis) it makes diploid cells, but in the second stage, it makes 4

haploid cells.

Question 12Fill in the blank. Crossing over and

_____ lead to genetic variation.A. Duplicate Chromosomes

B. Independent assortment

C. Asexual reproduction

D. Fertilization

Answer 12

BIndependent assortment

Because duplicate chromosomes, fertilization, and asexual reproduction cannot lead to variation.

Question 13Cytokinesis occurs under this

stage of mitosis.A.Telophase

B.Metaphase

C.Anaphase

D.Interphase

Answer 13

ATelophase

Because it is the last phase

Question 14Fill in the blanks. Cell division is a

process that enables organisms to _____ and ________.

A.Divide and reproduce

B. Reproduce and distribute

C. Divide and grow

D. Grow and reproduce

Answer 14

DGrow and reproduce

Because during mitosis and meiosis, the cells grow and reproduce.

Question 15What phase of Mitosis is this cell in?

A. metaphase

B. anaphase

C. telophase

D. interphase

Answer 15

CTelophase

Because there is a cleavage furrow and the daughter chromosomes arrive at the poles.