Genetics Chromosomes and Mitosis

History: In order for life to continue, cells will need to go through the process of reproduction. During their observations of cell division, biologists discovered short stringy structures that suddenly appeared in the nucleus.History: In order for life to continue, cells will need to go through the process of reproduction. During their observations of cell division, biologists discovered short stringy structures that suddenly appeared in the nucleus.

They identified these structures as CHROMOSOMES. The term chromosome means “COLORED BODIES”, these structures were named as such because scientists were able to stain these structures with biological dyes. These colored bodies were the structures of the cell that carried the genetic material of the cell. They identified these structures as CHROMOSOMES. The term chromosome means “COLORED BODIES”, these structures were named as such because scientists were able to stain these structures with biological dyes. These colored bodies were the structures of the cell that carried the genetic material of the cell.

Chromosome Structure: In Eukaryotic cells, chromatin found in the cell nucleus is made of DNA and PROTEIN.In Eukaryotic cells, chromatin found in the cell nucleus is made of DNA and PROTEIN. The DNA found in chromatin is thin UNCOILED strands. In the center of these strands are special protein molecules called HISTONES. The DNA found in chromatin is thin UNCOILED strands. In the center of these strands are special protein molecules called HISTONES.

As cells divide, the chromatin changes physical characteristics, but the chemical makeup remains the same. After replication, chromosomes form two identical parts called a CHROMATID. The pair are referred to as “sister chromatids”. The area in which these two chromatids are attached to each other is called the CENTROMERE. As cells divide, the chromatin changes physical characteristics, but the chemical makeup remains the same. After replication, chromosomes form two identical parts called a CHROMATID. The pair are referred to as “sister chromatids”. The area in which these two chromatids are attached to each other is called the CENTROMERE.

CHROMOSOME NUMBERS : Each species have different number of chromosomes. Chromosome number as seen in the table does not represent complexity of the species.Each species have different number of chromosomes. Chromosome number as seen in the table does not represent complexity of the species. SpeciesNumberSpeciesNumber Amoeba50Redwood22 Cat32 Gold fish 94 Human46 Garden Pea 14

In all sexually producing species, chromosomes occur in matching pairs. The two members of each pair are called HOMOLOGOUS CHROMOSOMES or homologues. Each pair of these chromosomes are structurally different than the other pairs of chromosomes in that cell.In all sexually producing species, chromosomes occur in matching pairs. The two members of each pair are called HOMOLOGOUS CHROMOSOMES or homologues. Each pair of these chromosomes are structurally different than the other pairs of chromosomes in that cell.

When a cell contains both chromosomes of a homologous pair, the cell is said to be DIPLOID. Scientist use the notation “2N” to denote a diploid cell.When a cell contains both chromosomes of a homologous pair, the cell is said to be DIPLOID. Scientist use the notation “2N” to denote a diploid cell.

Humans contain 46 chromosomes, 23 homologous pairs.Humans contain 46 chromosomes, 23 homologous pairs. A cell that contains only one of each of the homologous chromosomes is referred to as HAPLOID. Scientist use the notation 1N to denote a cell that is haploid.A cell that contains only one of each of the homologous chromosomes is referred to as HAPLOID. Scientist use the notation 1N to denote a cell that is haploid.

MITOSIS : Mitosis is the process where a parent cell divides into two identical sets of cells. Most of the cells in our bodies are cells that divide through the process of mitosis. These cells are referred to as SOMATIC cells.Mitosis is the process where a parent cell divides into two identical sets of cells. Most of the cells in our bodies are cells that divide through the process of mitosis. These cells are referred to as SOMATIC cells.

This process changes the NUMBER of cells without changing the information in the DNA of the cells. When unicellular organisms such as yeast divide by the process of mitosis all new generations contain the same genetic information.This process changes the NUMBER of cells without changing the information in the DNA of the cells. When unicellular organisms such as yeast divide by the process of mitosis all new generations contain the same genetic information.

DIVIDING OF CELLS: There are certain TRIGGERS that let a cell know when it is time to divide. One of the major factors that triggers division, is cell size. Surface to volume area is a factor that affects the chemistry of a cell.There are certain TRIGGERS that let a cell know when it is time to divide. One of the major factors that triggers division, is cell size. Surface to volume area is a factor that affects the chemistry of a cell. Surface area affects the ability of the cell to transport nutrients into the cell and wastes out of the cell.Surface area affects the ability of the cell to transport nutrients into the cell and wastes out of the cell.

CELL CYCLE: Scientists summarize the process of cell division through a sequence of steps referred to as the CELL CYCLE.Scientists summarize the process of cell division through a sequence of steps referred to as the CELL CYCLE. The cell cycle consists of five events: 3 phases of INTERPHASE, MITOSIS, AND CYTOKINESIS.The cell cycle consists of five events: 3 phases of INTERPHASE, MITOSIS, AND CYTOKINESIS.

The first of these events is INTERPHASE. This is a period of cell growth and development. Mitosis is the period when the cell nucleus divides. Cytokinesis is the division of the contents into two daughter cells.The first of these events is INTERPHASE. This is a period of cell growth and development. Mitosis is the period when the cell nucleus divides. Cytokinesis is the division of the contents into two daughter cells.

INTERPHASE : Cells spend most of their time in this phase of development. Interphase has three periods that scientists have noted. G1 PERIOD is the first of these three periods. This is the time when the cell doubles in size.Cells spend most of their time in this phase of development. Interphase has three periods that scientists have noted. G1 PERIOD is the first of these three periods. This is the time when the cell doubles in size.

The next part of interphase is the S PERIOD. This is the time that DNA in the form of chromatin replicates.The next part of interphase is the S PERIOD. This is the time that DNA in the form of chromatin replicates.

The last period of interphase is the G2 PERIOD. This is the final phase and is another time of rapid growth. The amount of time that a cell is in INTERPHASE depends on the type of cell that it is. Some cells, such as nerve and muscle cells, do not move out of the G1 phase of interphase. Other cells may divide every 15 to 20 minutes.The last period of interphase is the G2 PERIOD. This is the final phase and is another time of rapid growth. The amount of time that a cell is in INTERPHASE depends on the type of cell that it is. Some cells, such as nerve and muscle cells, do not move out of the G1 phase of interphase. Other cells may divide every 15 to 20 minutes.

MITOSIS: After a cell moves from the G2 phase of interphase, there is a series of steps a cell undergoes that are part of mitosis.After a cell moves from the G2 phase of interphase, there is a series of steps a cell undergoes that are part of mitosis.

Prophase is the first of these steps. Prophase is a time when CHROMATIN coils and forms CHROMOSOMES. The nuclear membrane breaks down and dark cylindrical bodies form and move to opposite end of the cell. Spindle fibers form that attach to chromosomes.Prophase is the first of these steps. Prophase is a time when CHROMATIN coils and forms CHROMOSOMES. The nuclear membrane breaks down and dark cylindrical bodies form and move to opposite end of the cell. Spindle fibers form that attach to chromosomes. PROPHASE

Metaphase is the second phase of mitosis. Spindle fibers move the chromosomes to the center (equator) of the cell.Metaphase is the second phase of mitosis. Spindle fibers move the chromosomes to the center (equator) of the cell. METAPHASE

ANAPHASE Anaphase is the phase of mitosis when the centromeres separate and the chromatids divide and move to opposite ends of the cell.Anaphase is the phase of mitosis when the centromeres separate and the chromatids divide and move to opposite ends of the cell.

The final phase of mitosis is the beginning of two new cells. At this point, spindle fibers disappear, chromatids unwind, and a nuclear membrane reforms.The final phase of mitosis is the beginning of two new cells. At this point, spindle fibers disappear, chromatids unwind, and a nuclear membrane reforms. TELOPHASE

Cytokinesis : This is the final stage of cell division. During this step, two new cells are formed when the cytoplasm and organelles are divided. The process is different for animal cells compared to plant cells.This is the final stage of cell division. During this step, two new cells are formed when the cytoplasm and organelles are divided. The process is different for animal cells compared to plant cells.

In the animal cell, cytokinesis is complete when the CELL MEMBRANE pinches in two and the cell divides into two daughter cells.In the animal cell, cytokinesis is complete when the CELL MEMBRANE pinches in two and the cell divides into two daughter cells.

In plant cells, a cell plate forms to begin creating a new cell wall between the two new cells.In plant cells, a cell plate forms to begin creating a new cell wall between the two new cells.