3.24c Mitosis 3

- Interphase - unable to see the process of DNA replication
- The first sign that the cell is entering mitosis and DNA division is when we see the break down of the nucleus, this phase is known as the "Prophase", the membranes brake down and the chromosomes become visible. They are visible as a pair of chromatids.
- Once the nucleus is gone, inside the cell, a network of protein molecules known as the "Spindle" and the "spindle fibres" that extend from one pole of the cell to the other. This is the "Late prophase" - The pair of chromatids will move towards the spindle and join onto one of the spindle fibres at the centrameere
- "Metaphase" - the pair of chromatids are attached to the spindle fibre by the centrameere. Characteristics = the chromosomes are in the middle, arranged across the equator of the cell
- The "Anaphase" - the spindle fibre shortens, pulling one chromatid in one direction and another in the other direction. The pair of chromatids are move apart and move to the poles of the cell. The pair of chromatids are separated.
- "Telophase" - The nucleus begins to reform around the chromosomes at either end of the cell. This will be the new nucleus of the new cell. See the formation of two nuclei, two sets of chromosomes at opposite ends of the cell
- "Cytokinesis" - The cells splits in two - NOT part of mitosis. The cell begins to move in-words in the middle, dividing the cytoplasm in half and the membrane will fuse across the equator to form the two cells. They each contain a chromosome. Both cells have chromosomes that are the same as the parental cell.
- In humans, we don't see one pair separating, but 23 pairs separating at the same time

3.24b Mitosis 2

- Copying the chromosomes is a process called "DNA replication"
- In the process, the chromosome undergoes a copying process to form an identical copy of itself with all the same genes and all the same alleles
- The copies are held together by a structure around the centre region called the "centromere"
- While the chromosomes are in a copied pair held together by a centromere, we refer to them as a "pair of chromatids"
- The process takes place inside the nucleus while the nucleus is still intact. We can't see this process. This is known as the "interphase" of the cell cycle.

3.24a Mitosis 1

- Mitosis - a form of cell division which results in growth. The growth occurs by an increase in the number of cells
- Begin with a normal cell with its nucleus. The number of chromosomes in the nucleus is known as the "Diploid" number = 2n,
- For humans, 2n = 46
- Cats, 2n = 38
- In the process, the cell will divide into 2 cells, each with a nucleus. Each of the nucleus has a Diploid nucleus. These cells are identical (or daughter cells).
- Identical because:
1) Same number of chromosomes
2) Same set of chromosomes (meaning, if we choose one chromosome from one of the cells, another version of the same chromosome will be found in the other cell)
- The questions which rise from this process:
1) "How are the copies of chromosomes made?"
2) "How do they separate into the two cells?"

3.16 DNA and Genetic Information

- Chromosomes are likely to contain thousands of genes
- When the gene loci is expanded, you will find a double helix (because there are two helixes) and they appear to be parallel
- Once the two strands of the helix is expanded you will see what is holding the two helixes together
- The sections on the outside are known as the "sugar - phosphate backbone"and in the centre there are a group of molecules called "Bases", the four different types of bases are: Adenine, thymine, eytosine and guanine
- In the molecules, these bases are holding together the two helixes. They are held together by the pairing between: Adenine and thymine on one side and cytosine and guanine. These are known as the "base pairs". They are gluing together one side of the DNA double helix with the other.
- The order of the bases: A-C-T-G-A-A-C-C-A-G, it is this order that we call the "gene"
- The gene is inside the nucleus. It is defined as the order of the bases (ATGC) and the number of the bases which codes for the construction of a protein in the cytoplasm.

a gene is the order of the bases on one side of the double helix

3.15 Genes

- a section of a DNA molecule is called a gene
- Genes: Carries information which forms a characteristic of the organism, could be a blood group, petal colour (in a flower)
- The genes are located in the nucleus
- The information is passed to the cytoplasm and in the cytoplasm, the genetic information is transformed into a protein. The protein controls the production of the characteristic
- GENE(in the Nucleus) ---> PROTEIN(in the Cytoplasm)

3.14 Chromosomes

1.
- Chromosomes: are the genetic information within a cell
- Typical cell: a nucleus - when opened up, a number of chromosomes is found
- Chromosomes are composed of a molecule called DNA and this forms a shaped known as the "Double Helix"
- A section of this molecule are called "Genes" and one chromosome will have many genes (possibly thousands of genes)
- Each gene carries the information for the construction of a protein
- The protein gives us the characteristics associated with the gene, e.g. blood group - a gene controls the production of the protein which controls the production of the characteristic

2.
- Different organisms have different number of chromosomes (e.g. cat = 38, chicken = 78, chimp = 42, human = 46)
- Chromosomes are known to operate in pairs = homologous pairs
- The homologous nature is based on the length of the chromosomes
- If you go to the same "gene loci" on the homologous pair, you will find the same gene, therefore, we have two versions of each gene for one characteristic - these versions are called "Allels

3.1 Sexual and Asexual Reproduction

Sexual Reproduction:
1. Organisms that show reproduction: Sexes - male / female
2. Sexually reproducing organisms produce cells called "Gametes"= formed in the male of the sperm cell (in plants = pollen grain) and in the female of the egg cell (in plants = ovule)
3. Type of cell division that produces gametes = Meiosis - one of the effects: half the total adult number of chromosomes in the gamete cell.
In humans, total number of chromosomes: 46 per cell
In gametes, total number of chromosomes: 23 per gamete cell
Going from 46-->23 is the process of cell division called Meisosis
4. Find the process of Fertilisation - in which gamete cells (the sperm cell and the egg cell) fuse together
5. Population: variation - broad. Many differences in the individuals of a sexually reproducing population

Asexual Reproduction:
1. No such sexes exist in asexual reproduction
2. No gametes
3. No meiosis, there is mitosis in eukaryotic cells and binary fission in prokaryotic bacterial cells
in this process, the number of chromosomes is maintained constantly, a cell with 20 chromosomes will divide to produce two cells with 20 chromosomes each. The two cells are identical
4. No fertilisation
5. Small amount of variation due to mutation - mostly identical - clone

How do plants reproduce asexually?