Mitosis and Meiosis: Cell Growth and Division

Meiosis: Metaphase II

Pairs of sister chromatids line up at the center.

Mitosis' 4 Stages

1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

How many meter of DNA does the typical human cell have?

A typical human cell has about 2 meters of DNA. Before the cell can divide, all of this DNA must be copied and then the two copies separated so that each daughter cell ends up with a complete set of DNA.

Meiosis: Prophase I

Chromosomes shorten and thicken. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad. When "crossing over" occurs.

Characteristic Number of Chromosomes?

Each species has a characteristic number of chromosomes in each cell nucleus; humans have 23 pairs or 46.

Chromosomes Number in Gametes...

Egg and sperm cells must have half the number of chromosomes so that when added together, the zygote will have the proper number. Gametes are said to be haploid or 1N because they contain only one of each kind of chromosome.

Five major phases of Cell Cycle

G1 (first gap) S (synthesis) G2 (second gap) Mitosis Cytokinesis

Sexual Reproduction chromosomes...

If an organism is the result of sexual reproduction, it will have two sets of chromosomes. One set comes from the mother and one set comes from the father. These two sets are called homologous chromosomes.

What must happen before a cell can begin mitosis and when do these preparations occur?

It must form duplicates of its chromosomes.It must produce a supply of organelles for the two daughter cells.These preparations occur during the G1, S, and G2 phases of the cell cycle. These three (G1, S, and G2) are collectively known as interphase

Meiosis I

Meiosis I results in 2 haploid(1N) daughter cells. Each daughter cell has half the number of chromosomes as the original cell.

Meiosis

Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes. Occurs in the sex cells only: the egg and sperm. Purpose is to reduce the chromosome number of the egg and sperm by half. Meiosis, like mitosis, is preceded by the replication of chromosomes. Unlike mitosis, this replication is then followed by two divisions: meiosis I and meiosis II.

What are the two major steps of Cell Division?

Mitosis and Cytokinesis

Telophase

Nuclear membrane begins to form. Nucleolus returns. The cell begins to pinch in. This is called a cleavage furrow. The end result is two cells that are exact copies of each other

Asexual Reproduction

Offspring are produced by only one parent. Each parent passes ALL of its genes to the offspring.

Anaphase

The centromeres divide and the chromatids move to opposite sides of the cell. The microtubules begin to shorten and this pulls the chromatids apart to opposite sides of the cell. The microtubules begin to shorten and this pulls the chromatids apart to opposite sides of the cell.

Prophase

The chromosomes coil and thicken and become distinct from one another. The chromosomes are now visible. The nucleolus disappears. The chromosomes are doubled throughout their length. The centrioles separate and start moving to opposite ends of the cell. A spindle made of microtubules begins to form. The nuclear membrane fragments and the microtubules invade the nuclear area. The spindle is completely formed. During prophase the pairs of chromatids become attached to the fibers of the spindle.

Meiosis: Interphase

The chromosomes replicate. It is similar to chromosome replication of mitosis. Two identical sister chromatids are held together by a centromere.

"Crossing Over" During Meiosis

The exchange of genetic information (genes) between segments of homologous chromosomes during meiosis.During prophase I, each pair of chromatids lines up next to its homologue.

Result of "Crossing Over"

The result is that the offspring will receive a new combination of genetic information. This leads to variation in the offspring. Variation leads to adaption and change. These variations will cause some of the offspring to be better suited for their particular environment. If they are better suited for their environment, it is most likely that they will survive to reproductive age and pass these favorable variations on to their offspring.

Metaphase

The spindle fibers will push and pull the chromosomes. The chromosomes line up at the center of the cell.

Meiosis: Anaphase I

The tetrads break apart and the pairs move to opposite sides of the cell. Sister chromatids remain attached at their centromeres.

Homologous Chromosomes

The two copies of each chromosome, one coming from the mother and one coming from the father. Carry the same genes, but they may have different expressions of that gene.

Importance of Mitosis

The two new cells are exact duplicates. Insures that the new cells will be able to carry on the same functions as the mother cell.

Fertilization

The union of sperm and egg.

Cell Cycle Regulators...

There are many proteins found on the inside and the outside of the cell that regulate cell division. These proteins send out signals that prevent excessive cell growth. This keeps the tissues of the body from disrupting one another.

Centromere

specialized DNA sequence of a chromosome that links a pair of sister chromatids

Zygote

A fertilized egg

Asexual Reproduction Disadvantages

All of the offspring are exactly alike. There is no variation. The ability to adapt to a changing environment is greatly reduced.

Sexual Reproduction Advantages

All of the offspring are genetically different from each other.

The stages of meiosis I and II

Interphase Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II

Asexual Reproduction Advantages

It is faster Large numbers of offspring are produced. The parent does not have to find a mate.

Regulation of the Cell Cycle

The frequency of cell division varies with the type of cell. Skin cells divide frequently throughout our lives. Liver maintain the ability to divide but only do so on rare occasion - say to repair a wound. The most specialized cells, such as muscle cells and nerve cells, do not divide at all.

Meiosis: Anaphase II

The pairs of sister chromatids separate and move to opposite sides of the cell.

Meiosis: Prophase II

The pairs of sister chromatids start toward the center.

Sexual Reproduction Disadvantages

The parent must find a mate. Fewer offspring will be produced. It takes longer.

Mitosis

the division of the nucleus

Comparison of Mitosis and Meiosis

- Mitosis occurs in all cells of the body except egg and sperm. Meiosis only occurs in the formation of egg and sperm. - In meiosis, each diploid cell divides twice to produce a total of 4 cells. In mitosis each diploid cell divides once to form 2 cells. - In meiosis, each of the four cells contains half the number of chromosomes as the parent cell. In mitosis, each new cell contains the same number of chromosomes as the original cell. - In mitosis, the homologous pairs do not come together to form tetrads. There will be no crossing over in mitosis. In meiosis, the homologous pairs do come together to form tetrads. While the chromosomes are in tetrads, crossing over may occur. - In meiosis, the four haploid cells contain different combination of chromosomes from each other. In mitosis, the new cells contain identical copies.

Importance of Meiosis

1 (2N) cell -------> 4 (1N) cells Meiosis produces four haploid cells that are different. The chromosome number of the egg and sperm is cut in half to insure that the zygote will have the proper number of chromosomes.

Cytokinesis

At the end of mitosis, two nuclei have been formed. Each nucleus has an identical set of chromosomes. Cytokinesis is the division of the cytoplasm.

Chromosomes during eukaryotic cell division....

Each cell must first copy its chromosomes before cell division occurs. At the beginning of cell division, the chromosomes condense into compact, visible structures that are easily seen with a microscope. At the beginning of cell division, each chromosome consists of two identical "sister chromatids". These chromatids are connected at an area called a centromere.

Cytokinesis in Animal Cells

In animal cells, a cleavage furrow pinches the cell membrane inward until the cell is pinched into two separate cells. Each new cell contains its own nucleus, cytoplasm, and organelles.

Meiosis in males and females.

In males, meiosis results in 4 sperm cells. In females, 4 cells are produced, but only one will become an egg cell. All of the cytoplasm and all of the organelles are put into one egg cell. The other three cells will never be functional.

Cytokinesis in Plant Cells

In plants, it is not possible for the cell to pinch inward because of the rigid cell wall. In plants, a cell plate forms midway between the two nuclei. The cell plate continues to form across the cell until two separate cells have been formed

Results of Mitosis

In unicellular plants and animals, it results in new offspring by asexual reproduction. In multicellular organisms, it results in the growth and repair of the organism.

Haploid

Means there are one of each kind of chromosome in each cell. The symbol is "1N".

Diploid

Means there are two of each kind of chromosome in each cell so the cells contain two complete sets of chromosomes. The symbol for diploid is 2N. "N" is the number of different chromosomes an organism has. Humans are 2N because we have 2 of each kind of chromosome. So in Mitosis 1 (2N) cell -------> 2 (2N) cells.

Sexual Reproduction

Sexual reproduction requires two parents. Each parent passes on HALF its genes to its offspring. Must have male and female: male to produce sperm and female to produce eggs.

Meiosis: Metaphase I

Tetrads line up at the center of the cell.

Meiosis II

The Meiosis of the 2 Haploid(1N) daughter cells.Results in 4 new cells that are 1N.

Why do cells divide instead of growing larger?

Two main reasons. If cells grow too large, it will have trouble moving enough nutrients and lasts across the cell membrane. Secondly, the larger a cell becomes, the more demand the cell places on the DNA.

What is cancer?

Uncontrolled cell growth. Cancer cells do not respond to the signals that regulate the growth of cells. Cancer cells divide uncontrollably and form masses of cells called tumors.

Tetrad

consists of 4 chromatids.

Chromatid

each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA

The Cell Cycle

the life of the cell from the time it is first formed from a dividing parent cell until its own division into two cells.

Cell Division

the process by which cellular material is divided between to new daughter cells. 1 Mother cell= 2 Daughter cells

Interphase

the resting phase between successive mitotic divisions of a cell, or between the first and second divisions of meiosis. Stages G1, S, and G2 in the cell cycle.

G2 phase of the Cell Cycle

The cell assembles the special structures needed for cell division

G1 phase of the Cell Cycle

The cell doubles in size. The enzymes, cytoplasmic organelles and other molecules double in number.

Meiosis: Telophase I

The cell separates into two cells.

S phase of the Cell Cycle

Replication of DNA occurs.

Meiosis: Telophase II

Results in 4 new cells that are 1N.

Gametes

Sex cells (egg and sperm)