Mitosis

3.24 a. Understand that the division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.

Remember that mitosis is a form of cell division which results in growth. And that growth occurs by an increase in the number of cells.

The number of chromosomes in the nucleus is called the diploid number (2n)
For humans 2n = 46, for cats 2n = 38.

In the process of mitosis, the cell will divide into two cells both with a nucleus each. Inside the nucleus we find that each cell has a diploid nucleus. These cells are identical. Sometimes called daughter cell.

They have the same number of chromosomes and they have the same set of chromosomes.



3.24 b. Understand that the division of a diploid cell by mitosis produces cells which contain identical sets of chromosomes.

The initial cell has to copy the chromosomes it has. Copying the chromosomes is a process called DNA replication. In this process each chromosome undergoes a copying process to form an identical copy of itself.

With all the same gene and alleles and these two copies are held together by a structue arround the center region known as the centro-mere (Holding the two chromosomes together).

We refer to these cells as a pair of Chromatids.

during this process the nucleus is still intact. Which means you cannot see this process happening.

This is known as the Interphase of the cell cycle.

3.24 c.

DNA replication occurs during the Interphase

First sing that a cell is entering the process of mitosis, is when we see the break down of the nuclear membrane. The nucleus breaks down.

This is a phase known as the pro phase. When it breaks down, the chromosomes become visible.

With the nucleus gone, inside the cell a network of protein molecules known as the spindle, and the spindle fibers, and these extend from one pole of the cell to the other.
What occurs during late prophase, is that the chromosome pair will move toward the spindle and join one of them at the Centromere.

Next we have the Metaphase. During which the chromosomes are in the middle arranged along the equator of the cell.

Then we have the Anaphase. In the Anaphase the fiber shortens pulling the two Chromatids appart.
Here we have the separation of the pair.

The end of mitosis is at the stage of Tilophase. When the nucleus begins to reform around the chromosomes at either end of the cell. this will be the new nucleus of the new cell.



A phase know as cytokinesis where the cell splits into two (this isn't regarded as part of mitosis)

DNA and genetic information

3.16 Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with Thvmine (T), and Cvtosine (C) with guanine (G).

Chromosomes are likely to contain thousands of genes.

At the gene loci you find a double helix.
They appear to be parallel.


These bases are holding together these two helix.

They are held together by pairing A - T and C - G.
These are known as the base pairs. This is always found in the DNA.

The order of molecules: A-C-T-G-A-A-C-C-A-G is what we call a gene.
The order of the basses ATGC and the number of the bases.

Genes

3.15 Understand that a gene is a section of a molecule of DNA

DNA molecule Example

This is showing the double helix shape characteristic.

This gene caries the information that forms that characteristic of the organisms. This could be a blood group, or even an eye color.

They are located in the nucleus. And the information is passed to the cytoplasm the genetic information is transformed into a protein which controls the production of the characteristic.

Chromosomes

3.14 Recall that the nucleus of a cell contains chromosomes on which genes are located.

Chromosomes= Genetic information of the cell.
If you opened a nucleus up you would find chromosomes

It is composed of a molecule called DNA (Deoxyribo nucleic acid) which forms a shape known as the double helix.


Sections of this molecule are called genes. And one chromosome will have many genes (possibly thousands)
Each gene contains the information for the construction of a protein. The protein gives the characteristic associated with the genes (e.g. blood group).


Different organisms have different number of chromosomes.
Cat 38, Chicken 78, Chimp 42 and human 46.


Chromosomes are known to operate in pares known as homologous pairs. 
 
If you go to the same loci on the homologous pair you'll find the same gene.


So there are 2 versions of each gene for 1 characteristic.
These versions are called Alleles.

Sexual and Asexual reproduction

3.1 Describe the differences between sexual and asexual reproduction

Organisms that show sexual reproduction show sexes which helps us identify a male and a female.
In Asexual reproduction there are NO sexes.



Sexually reproducing organisms produce cells called Gametes, which tend to form in the Male (Sperm cell) and in the female (egg cell)
Asexually reproducing organisms, don't have Gametes.

The type of cell division that produces Gametes is called meiosis which has a number of effects. One of these effects is to half the total adult number of chromosomes in the Gamete cell. In Humans the total number of chromosomes is 46 per cell but in gametes the total is 23. Going from 46 down to 23 during reproduction is the process of meiosis
In Asexual producing populations there is no meiosis but there is mitosis in ucariotic (how do you spell?) cells and binary fissim procariotic (How do you spell?) bacterial cells. In this process the number of chromosomes is maintained constant (eg. a cell with 20 chromosomes is divided into two cells which 20 chromosomes. These 2 cells are identical.

In sexually reproducing population you find the process of fertilization. In which gamete cells fuse together (Male and female)
In asexual reproduction there is no fusing and no fertilization.


In the population of sexual reproducing organisms you find variation (differences). It is broad.
In asexual reproducing population, there is a very small variation in the population which is mainly because of mutation. Otherwise they are identical. This is known as a clone.