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MITOSIS & MEIOSIS Bio Review

MITOSIS Part 1

THE CELL CYCLE AND MITOSIS

Due to the loss and death of cells must replace them.

How many cells in your body? 50-100 million trillion

Every minute your body produces about 300 million new cells

Three stages in the cell cycle:

1. Interphase: cell carries out normal functions.

2. Mitosis: nucleus contents duplicated and divided intotwo equal parts.

3. Cytokinesis: separation of two nuclei and cell contentsinto two daughter cells.

PARTS OF THE CELL CYCLE

INTERPHASE

Interphase - the longest cell cycle stage (lasts 15 hrs. – months).

cell performs normal functions and grows.

In late interphase, DNA copies itself in the process of replication.

Replication involves several steps:

1. The DNA molecule unwinds with the help of an enzyme.

2. New bases pair with the bases on the original DNA.

3. Two new identical DNA molecules are produced.

Now, double the amount of DNA in nucleus it divides (Mitosis)

DNA UNRAVELING (VIDEO)

LATE INTERPHASE CONT’D.

Chromatin is in its loosely coiledform so that DNA can be copied into RNA for proteins to be made in preparation for cell division.

At the end of interphase, the cell continues to grow and make proteins in preparation for mitosis and cytokinesis.

CHROMOSOMES

As the nucleus prepares to divide, replicated DNA in interphase joins to form sister chromatids, joined by a centromere.

MITOSIS OVERVIEW:

Mitosis is the shortest stage of the cell cycle where the nuclear contents divide, and two daughter nuclei are formed.

It occurs in 4 stages: 1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Helpful saying to remember the order: “I picked many apples today.”

MITOSIS - PROPHASE

Chromosomes start to coil and become visible.

Pairs of centrioles start to separate.

The nuclear membrane disappears.

Spindle fibers start to form between the centriole pairs.

Chromosomes move more evenly throughout the nucleus.

MITOSIS - METAPHASE

Centriole pairs move to opposite ends of the cell.

Spindle fibers are still attached to the centriole pairs.

Chromosomes line up along the midline of the cell and are attached to the spindle fibers.

MITOSIS - ANAPHASE

The pair of chromatids split at the centromere and move to opposite ends of the spindle.

Now there are twice the number of chromosomes within the cell membrane.

Movement of the chromosomes towards the opposite ends of the cell membrane is aided by the spindle fibers.

MITOSIS - TELOPHASE

Nuclear membranes formaround the two new sets of chromosomes.

The spindle fiber disappears.

Chromosomes start to uncoil (chromatin) and become less visible.

Cell starts to make a groove (furrow) in the middle to eventually split into two identical cells.

CYTOKINESISThe division of material outsideof the nucleus.Occurs after telophase.

Divides the organelles and other substances in the cytoplasm into roughly two equal halves.

Animal cells furrow while plant cells form a cell plate

# chromosomes in daughter cell = the # chromosomes in parent cell.

Daughter cells are genetically identical to parent.

Video on Mitosis

MEIOSIS Part 2

OBJECTIVES

By the end of the lesson you should be able to:

Describe the process of meiosis

Compare and contrast meiosis and mitosis

Explain why meiosis is needed

MEIOSISSexual reproduction – 2 parents – genetic differences

The process of Meiosis results in the production of special cells called gametes

Gametes have half the number of chromosomes as body cells

MEIOSISCell division occurs twice in Meiosis

Once at the end of Meiosis I and again at the end of Meiosis II

In Meiosis I, matching chromosomes are called homologous chromosomes separate

In Meiosis II, sister chromatids separate

MEIOSISThe process of meiosis shuffles genetic information and results in variation of the gametes

Genetic diversity

MEIOSIS

AKA: Germ cell division

Purpose: to produce gametes (i.e. sex cells: sperm and egg)

Products: 4 haploid cells each genetically different this creates genetic variability

TERMS:Haploid: half the total number of chromosomes found in gametes (in humans = 23)

Diploid: total number of chromosomes found in body cells (in humans = 46)

FERTILIZATION

2 gametes come together; in humans an egg and sperm come together

Each has 23 chromosomes, thus together there is 46 in the zygote

23 23

46

+ Gametes: why is the

sperm smaller than the

egg?

Zygote: will grow (by

mitosis) into a baby in

~9 months

MEIOSIS: REDUCING CHROMOSOME NUMBER

NUMBER OF CHROMOSOMES SEQUENCE

46

92

4646

23232323

All genetically different

Parent Cell

Daughter

Cells

CHROMOSOME SEQUENCE

Meiosis Video

Meiosis 2 Video

MEIOSIS – PROPHASE I

Chromosomes coil and become visible.

Nuclear membrane disappears.

Spindle fibers form.

Homologous chromosomes move towards each other and pair.

MEIOSIS – METAPHASE I

Pairs of homologous chromosomes move to the midline of the cell.

These pairs are aligned on either side of the metaphase plate.

MEIOSIS – ANAPHASE I

Homologous chromosome pairs are pulled away from each other towards opposite ends of the cell.

Paired chromatids remain attached.

MEIOSIS - TELOPHASE I

Paired chromatids may uncoil and become less visible.

Nuclear membranes may form around each chromosome cluster.

Spindle fibers disappear.

Cytokinesis occurs.

MEIOSIS II

Phase II of meiosis is the mitotic division of haploid cells.

Although there will be four new non-identical cells at the end of meiosis II, all other processes for this division are similar to mitosis.

MEIOSIS II – PROPHASE II

Paired chromatids coil.

Spindle fibers form.

Nuclear membrane disappears.

MEIOSIS II – METAPHASE II

Paired chromatids line up in the middle of the cell.

The chromatids are attached to spindle fibers.

MEIOSIS II – ANAPHASE II

Each pair of chromatids split at the centromere to form two independent chromosomes.

Chromosomes move to opposite ends of the cell.

MEIOSIS II – TELOPHASE II

Chromosomes uncoil and become less visible.

Nuclear membranes from around four new nuclei.

Spindle fibers disappear.

Cytokinesis occurs.

Meiosis Square Dance

MEIOSIS - CYTOKINESIS

Same process as in mitosis.

Four non-identical cells are formed.

These cells are called haploid cells (n).

# chromosomes = half the # of chromosomes of parent cell.

MEIOSIS EVENTS

Meiosis I

Matching chromosome pairs (homologous chromosomes)

move to opposite poles of the cell -two daughter cells result.

Meiosis II

Chromatids of each chromosome are pulled apart - the end result is four haploid cells, each with half the number of chromosomes. These develop into gametes.

CROSSING OVER

Important event that occurs between each chromosome pair in meiosis I

There is an exchange of segments of DNA and picks up new genetic information

INDEPENDENT ASSORTMENT

This occurs when homologous pairs of chromosomes separate at the equator and move towards opposite poles of the cell.

Video

Mitosis

vs Meiosis

FERTILIZATION

There are more than 8 million combinations possible for these 23 pairs in any egg or sperm cell

When fertilization occurs, 70 trillion different zygotes are possible from the combination of one sperm cell and one egg cell!

GAMETE FORMATION

Males produce 4 sperm for every round of meiosis

Females produce one egg for each round of meiosis: 3 of the 4 “eggs” produced die off - called polar bodies

All the cytoplasm, nutrients and energy gets put into one egg