MITOSIS

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3.24c Mitosis 3 - Stages

1. Interphase - DNA replication occurs

2. When Mitosis begins, the nucleus begins to break down. - Called the PROPHASE - The membrane breaks down and the chromosomes become visible - 2 together called chromatids

3. After that, a network of protein molecules called the spindle grow. - called LATE PROPHASE - This is where the chromosome pair move and join to spindle

4. METAPHASE - The spindle fibre and the chromatid is attached together through the centromere - The chromosomes are in the middle - across the equator of the cell.

5. ANAPHASE - The fibre shortens, splitting the chromatids - They move apart and move to the poles of the cell - Becoming a separate pair of chromatids

6. TELOPHASE (the end) - the nucleus begins to reform around the chromosomes of either cell. - The formation of 2 cells from the separate nuclei - opposite cells

7. CYTO KINESIS - When the cell splits into 2 - NOT PART OF MITOSIS

3.24b Mitosis 2

1. After the cell divides into 2 - they have the same number of chromosomes and the same exact ones - meaning that the cell has to copy its chromosomes

2. The copying of the chromosomes is called DNA replication - The 2 copies then come together and are held by the centromere - they become a pair. They become a pair of CHROMATIDS

3. Takes place inside the nucleus - Called the interphase of the cell cycle

3.24a Mitosis

1. Mitosis - form of cell division - leads to growth - increase in a number of cells

2. A cell has 46 chromosomes - this is called a diploid number. The human diploid number (2n) = 64

3. The cell will divide to 2 cells. - the 2 cells have a diploid nucleus - They are identical - They have the same number of chromosomes and they have the same set of chromosomes - Identical chromosomes

3,16 DNA and Genetic information

1. Chromosomes are likely to contain thousands of genes > When you expand a chromosome, you will see a double helix, which appears to be parallel.

2. Holding the 2 strands of the helix is the sugar phosphate backbone > In the center, we find a group of molecules called bases > Adenine > Thymine > Cytosine and Guanine.

3. In the molecule, the bases hold together the two helixes > held together by Adenine and Thymine , and Guanine and Cytosine > these are known as base pairs > the base pairs glue one side of the DNA to the other

4. The gene has the order of bases and the number of bases > this codes for the construction of a protein in the cytoplasm > this gives the characteristic

A gene is the order of the bases on one side of the double Helix

3.15 Genes

1. A gene is a section of a molecule of DNA > DNA = double helix form

2. A gene forms the characteristics of the organism. > could be a blood group or a petal colour in a flower.

3. Different genes for different purposes

4. Genes are in the nucleus > info passed to the cytoplasm > then transformed into a protein > the protein controls how much of the characteristic is used.

3.14 Chromosomes

1. Chromosomes > genetic information within a cell

2. Cell > Nucleus > Chromosomes

3. Chromosome is composed of a molecule known as DNA - Deoxyribo nucleic acid > forms a shape known as the double helix

4. Sections of the molecule are called genes > one chromosome has many genes > possible thousands

5. Each gene carries the information for the construction of a protein > the protein gives characteristic associated with the gene > eg. a blood group

6. Different organisms have a different number of chromosomes > Cat = 38 > Chicken = 78 > Chimp = 42 > Human 46

7. Chromosomes are known to operate in pairs > pairs known as homologous pairs > homologous nature is based on the length of the chromosomes

8. The gene loci, between the homologous pair, we will find the same gene on both sides > giving 2 versions of each gene.

9. Versions are called alleles

3.1 Sexual and Asexual Reproduction

1. Organisms that show sexual reproduction show sexes >; can identify what is male and female

2. Asexual > Cannot differentiate between male and female

3. Sexually reproducing organisms produce cells called gametes > take the form in the male of the sperm cell > and in the female of the egg cell

4. in plants, the sperm cell is knows as the pollen grain > the egg is knows as the ovule

5. Asexually reproducing populations have no gametes

6. The type of cell division that produces gametes is called meiosis > Effects is to half the total number of chromosomes in the gamete cells. > offspring has half for both

7. There is a total of 46 chromosomes per cell. In gametes, there is only 23, per gamete cell.

8. Halving the chromosomes per cells to gametes is called meiosis

9. In asexual reproduction, there is no meiosis, mitosis and binary fission.

10. In this process, the number of chromosomes is remained constantly. > EG - a cell with 20 chromosomes will divide to make 2 cells with 20 chromosomes in each.

11. Sexually reproducing > process of fertilisation > egg and sperm cell fuse together

12 Asexual, there is no gametes, therefore no fertilisation

13. Sexually producing > variation between offspring > broad variation

14 Asexual have a very small amount of variation due to mutation > knows a clone

Question -- Why dont asexually reproducing organisms vary? Is this because they make cloned cells with the same number of chromosomes?