3.24) Mitosis (a-c)

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

Mitosis - cell division which results in growth which occurred by increase in number of cell

A normal cell with its nucleus. The number of chromosome in the nucleus is called the diploid number (abbreviated 2n). For human, 2n = 46. 

In the process known as mitosis, a cell will divide into two cells, each with a nucleus. Each nucleus contains diploid number of chromosomes. The two cells are identical in which sometimes are described as daughter cells.

- They have the same number of chromosomes.

- They have the same set of chromosomes. 

How are the copies of chromosomes made? How did they separate into two cells?

The original cell has to copy its chromosomes in the process called DNA replication. In this process, each chromosome undergrowth and copy process to form an identical copy of the cell with the same genes and same alleles. The two copies are held together by a structure around the center region known as the centromere. The pair is called pair of chromatids. 

The process of DNA replication takes place inside the nucleus while it's still intact. This resting stage of cell cycle is known as the interphase. 

The Stages of Mitosis

During the interphase, the process of DNA replication occurs. We are not able to observe the chromosomes.

1. Prophase: Nuclei member breaks down and the chromosomes become visible as a pair of chromatids.

2. With the nucleus gone, inside the cell, a network of protein molecules known as the spindle/ spindle fibres formed. This extends from one pull of the cell to the other. Late prophase: The chromosome pairs will move toward the spindle and will join with the spindle fiber in the center. 

3. Metaphase: The pair of chromatids are attached to the spindle fibre by the centromere. The characteristic is the chromosomes are in the middle across the equator of the cell.

4. Anaphase: The spindle fiber shortened, pulling each chromosome in opposite direction and the pair of chromatids are moving apart toward each poles. (They're separated.) 

5. Telophase: The nucleus beings to reform around chromosomes at either end of the cell. (The formation of two nuclei at opposite ends of the cell.) 

6. Cytokinesis: The cell splits into two. This is NOT part of mitosis. It is a particular independent stage. 

The daughter cells each contain a chromosome, which is the same as the parental cell. In human cell, we see 23 pairs of chromosomes separating at the same time. 

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)

A chromosome is likely to contain thousands of genes. Taking one gene locus and expand the small section of chromosome will find the Double Helix shape, which appears to be parallels. 

The strand of the Double Helix are called the "Sugar-phosphate backbone." 

In the centre we find a group of molecules we called "bases" and there appears to be 4 different types of bases --- adenine (A), thymine (T), cytosine (C ), and guanine (G).

In the molecule these bases are holding together to the two helixes. They're held together by the following paired bases:

Adenine and Thymine

Guanine and Cytosine

They are called base pairs (nitrogenous bases). They're always found in DNA. 

Notice that the bases on one side of Helix have specific order: A, C, T, G, A, A, C, C, A, G.The order create up a gene. 

Gene is inside the nucleus, so the gene is defined as order of bases (ATGC) and the number of the bases. Both of them are important information for the construction of protein in the cytoplasm. It also gives the characteristic.
DNA molecules can also copy itself, which copies the genetic code exactly. This is important because to an extent they must copy and divide itself --- mitosis. 

3.15) Genes

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

DNA - deoxyribonucleic acid 

Double Helix shape

One section of molecules is called genes.

The gene carries characteristics which can be blood group, petal color, etc.

The genes are located in the nucleus and the information is passed to the cytoplasm, where it's transformed into protein. This protein controls the production of the characteristic.

How information is carried: Gene (in the nucleus) ----> Protein (cytoplasm)

3.14) Chromosome

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

Chromosomes are the genetic information in cells.

Cell ---> Nucleus ---> Chromosomes ---> DNA

The structure of a Chromosome

A chromosome is composed of DNA (deoxyribonucleic acid) which formed the shape known as the "double helix."

Each section of a chromosome is called genes. A chromosome contains thousands of genes. Each genes carry the information for the construction of protein.

Protein gives us the characteristic associated with the genes. For example, blood group.

Different organisms have different number of chromosomes per cell. 

- Cat - 38

- Chick - 78

- Chimpanzee - 42

- Human - 46 

Chromosomes operate in pairs known as the homologous pairs.

The homologous nature is based on the length of the chromosome. 

Some of the homologous pairs within an organism.

Gene loci are the specific locations or DNA sequence on a chromosome. 

If we go to the same position on the other chromosome in a homologous pair, we found the same gene loci (which contains another gene). Therefore we have 2 versions of each genes for one characteristic. These characteristics are called alleles, which is the variant of DNA sequence at a given locus.

Homologous chromosomes and gene loci

Question: Since there are 46 chromosomes per cells, is each chromosomes responsible for genes of different characteristic?

3.1 Sexual and Asexual reproduction

describe the difference between sexual and asexual reproduction

Sexual Reproduction

- show genders (Male/ Female)

- produce cells called gametes (sperm- male, egg- female)

- meiosis (cell reproduction which produces gametes) …
half total number of chromosome in the gamete cells 

for example, in human, the total number of chromosome in adult human is 46 but only 23 in gamete cells

- ferterlisation (in which sperm cell and egg cell fuse together)

- broad variation (many differences in the individuals)

Asexual Reproduction

- no genders

- no gametes

- mitosis (in eukaryotic cells)/ binary fission (in prokaryotic bacterial cells)

in this case, the number of chromosomes is maintain constantly throughout

- no ferterlisation

- small variation or identical (clone) due to mutation

Question:
What are the factors that determine whether an organism reproduces sexually or asexually?