Review of Cell Division & Basic Genetic Principles.

Review of Cell Division & Basic Genetic Principles

1) For single-celled organisms to reproduce.

2) For multicellular organisms to grow and repair.

3) For the replacement of damaged cells.

What is the Purpose of Cell Duplication?

The Cell Cycle

Most of the time, the cell is in Interphase Cell growth, DNA replication PREPARATION FOR MITOSIS

The Cell Cycle (continued)

G1 - growth phase 1 cytokinesis (division of the cytoplasm), cell cytoplasm grows,

organelles are reproduced.

S - synthesis phase DNA replication

G2 -growth phase 2 Growth and preparation for cell division.

Mitosis division of the nucleus (4 phases)

Some Important Terminology

Cells ‘normal’ chromosome number is known as the diploid number and is represented as 2N.

Diploid because all chromosomes belong to a set or pair.

Human diploid number is 46 23 pairs of chromosomes.

Cells can be 4N (tetraploid) just prior to mitosis.

Cells can also be 1N or haploid in the case of sperm or egg (meiosis).

Interphase: “Getting Ready for Mitosis”

Because DNA must be split evenly between the two cells it initially replicates and condenses (coils up into tight bundles) into a chromosome - two sister chromatids separated by a centromere.

Chromosome centromere

sister chromatids

Chromosomes

During interphase are long thin strands known as chromatin

Upon replication, two strands of chromatin are joined at centromere

During prophase when they are visible, individual strands of chromosomes are called chromatids

chromosome

chromatid

Centromere

Mitosis Stage 1: Prophase

Nuclear membrane disappears

chromatin fibres become short, thick and visible

centrioles move to opposite poles of cell creating spindle fibers and astral rays

NOTE – no centrioles in plant cells

Mitosis Stage 2: Metaphase

• Chromatid fibres line up along the equatorial plate of cell.

• Spindle fibres attach at the kinetochore, which is located at the centromere of each chromosome.

Mitosis Stage 3: AnaphaseChromatid fibres are

drawn towards the ends of the cell

centromeres replicate

Chromatids appear to follow the path made by the spindle fibres

Mitosis Stage 4: TelophaseTwo new cells begin to

form as cytoplasm pinches off at cleavage furrow

nuclear membrane forms around two new nuclei

spindle fibres, astral rays disappear

Cytokinesis = splitting of two daughter cells

Mitosis Video

http://www.youtube.com/watch?v=VlN7K1-9QB0

Mitosis in Plant Cells

Similar to animal cell division, except:

no centriolesduring telophase when

two daughter cells form, cells are divided by cell plate

Structure of Genetic Material

What do you think this is?

DNA.. What is this short for?

Deoxyribonucleic Acid

DNA, Chromatin, & Chromosomes

DNA is part of a chromatin fibre, which condenses to form chromosomes.

DNA

The Secret of Life – The Discovery of DNA (Watson & Crick in 1953)

http://www.youtube.com/watch?v=sf0YXnAFBs8

a long, double stranded molecule, that contains the “information” of an organism

a gene is a segment of DNA that encodes for a specific piece of information/trait (e.g. the gene for eye colour)

a genome is the complete sequence of DNA in an organism.

Important Terminology Sex Chromosome = a chromosome that determines the sex (male or

female) of an organism.

Autosome = a chromosome that is not involved in determining the gender of an organism.

Chromatid = half of a chromosome

Sister Chromatid = one of the two duplicated chromosomes

Homologous Chromosomes = pairs of chromosomes carrying different forms of the same gene (e.g. one homologous pair encodes for blue eyes, the other homologous pair encodes for brown eyes, but they both encode for eye colour).

Allele = a different form of the same gene (e.g. one allele encodes for black hair vs. another allele that encodes for blonde hair).