3.24c Mitosis 3

Stages of Mitosis

1. Interphase - Resting stage
DNA replication
Unable to see chromosomes

2. Prophase - Nucleus membrane breaks down
Chromosomes are now visible
Pair of chromatids
Beginning of mitosis

3. Late Prophase - Chromatids move towards spindles
Network of protein molecules (Spindle / fibres)
Extend from one pole of the cell to the other

4. Metaphase - Centramere joins to spindle fibre
Chromosomes are in the middle

5. Anaphase - Separation of the pair of chromatids
Spindle fibre shortens
Pulls chromatids apart
Move to the poles of the cell

6. Telophase - End of mitosis
Nucleus begins to reform around the chromosomes
Formation of two nuclei
Two sets of chromosomes at opposite ends of the cell

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Cytokinesis - Cell splits into two
NOT part of mitosis
Membrane fuses across the equator to form two new cells
Both cells have one chromosome - Same as the parental cell

Source: http://www.ba-education.com/dna/mitosis.jpg

3.24b Mitosis 2

How are copies of chromosomes made?

DNA replication
- Chromosome copies itself
- Held together by centromere
- 'Pair of chromatids'

Source: http://www.youtube.com/watch?v=f3c36gGDlRg

- Takes place inside the nucleus when it is still intact
- Process cannot be seen
- Interphase of cell cycle

3.24a Mitosis 1

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

Mitosis - Form of cell division -> Growth / Increase in the number of cells

Number of chromosomes in a cell - Diploid number (2n)
Humans - 2n = 46
Cats - 2n = 38
etc…

After cell division
- Each cell has a diploid nucleus
- Both cells are identical / daughter cells
- Inside the nuclei:
1. Same number of chromosomes
2. Same set of chromosomes (Duplicated)

Source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEHtB-J0eLzuY29DfQ-kV0iHFOg9UHrLKaXA8FLJPA1bIAkVROoYAzl_Cy-bD403KqMyVNoFlGrEXqbInMT57_F6IVASWO1c5UOfgeZ0bOqd-wtAIBiR6qFR99zSIuXebd7igkfPPrWK4/s320/mitosis.gif

3.16 DNA and Genetic Information

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 thymine (T), and cytosine (C ) with guanine (G)

Chromosomes are likely to contain thousands of genes
Position on it a gene loci
Expanding a gene loci -> double helix

Double helix
Parallel
Expanding small section holding double helix together -> Helixes

Helixes are called sugar-phosphate backbone

Source: http://ghr.nlm.nih.gov/handbook/illustrations/dnastructure.jpg

Centre - group of molecules called bases
(4 types of base - adenine, thymine, cytosine, guanine)
Base pairs: A-T and G-C

Example of gene - ACTGAACCAG
Order of the bases -> The order is a gene

Nucleus - Order of bases (ACTG)
- Number of bases

Source:  http://www.youtube.com/watch?v=CEBmnfLWDQs

Gene (nucleus) -> Protein (cytoplasm) -> Characteristic

A gene is the order of the bases on one side of the helix

3.15 Genes

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

Source:  http://www.youtube.com/watch?v=-GPZCggg2lA

DNA - double helix shape

A section of DNA is called a gene
Gene carries information which forms the characteristic of organism
e.g. blood group, petal colour, etc. (different genes for different characteristics)

- Genes are located in the nucleus
- Information is passed to the cytoplasm
- Information is transformed into protein (inside cytoplasm)

Information flow:
Gene (nucleus) -> Protein (cytoplasm)

3.14 Chromosomes

Recall that the nucleus of a cell contains chromosomes in which genes are located

Chromosomes - Genetic information within a cell in the nucleus

1. Chromosome composed of molecule called DNA
- takes shape of double helix

Sections of DNA are called genes
- 1 chromosome can have thousands of genes

Source: http://www.elmhurst.edu/~chm/vchembook/images/580dna.gif

Each gene carries information for construction of protein
Protein gives characteristic associated with gene (e.g. blood group)

DNA (Gene) -> Protein -> Characteristic

2. Different organisms have different numbers of chromosomes
e.g. Cat 38, Chicken 78, Chimp 42, Human 46 (chromosomes per cell)

3. Homologous pairs - genes operating in pairs

Source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiV4AMLxhPmVPzgztkcFYq64mZVeEWsFfljGLIf9-JLwnV4FMg2qdOsCaT0W_B8O5gbU-9SiNKN2sO0WE8C7l_w6E0cWfAdjnK-PZM1ETUsqhyphenhyphenPcKbY4ExnSmUPVS-a2A7xwH02TqQn2g-i/s400/female+karyogram.jpg

Homologous nature is based on length of chromosomes

Location of gene - gene loci
Same gene loci on homologous pair - same gene

-> 2 versions of each gene for one characteristic
-> Versions are called alleles

http://www.monteweston.com/Biology/Bio/joalleles.gif

3.1 Sexual and Asexual reproduction

Describe the differences between sexual and asexual reproduction

1. Sexes
- Exist in sexual reproduction - male/female
- None in asexual

2. Cells
- Sexual reproduction needs gametes
- Sperm - male
- Egg - female
- Asexual - no gametes

3. Cell division
- Sexual reproduction - Meiosis - ½ total adult number of chromosomes in gamete cells
- In humans the number of chromosomes in each cell is 46 - in gamete cells there are 23 per cell
- Asexual reproduction - Mitosis / Binary fission
- The number of chromosomes is constant (two cells are identical)

4. Fertilisation
- Sexual - egg cell and sperm cell fuse together
- Asexual - no fertilisation

5. Variation / Difference
- Sexual - broad + many differences
- Asexual - small variation (due to mutation), almost all identical (clone)

What are some examples of genetic mutation in asexually reproducing species?