Notes on Chromosomes, Mitosis, &

Meiosis

What is a chromosome?• Chromosomes = condensed DNA,

same material, coiled more tightly into individual bundles

• Chromatin = DNA that is uncoiled, unorganized, not individually visible

• DNA is a large polymer composed of sugars, phosphates, & ‘bases’.

Chromosomes 400x1 arm of achromosome

Chromatin wrapped >>around histone proteins

Chromatin w/o histone proteins

DNA molecule

History of discovery

• First seen and named “colored bodies” by Flemming in 1882

• Similarity to Mendel’s factors noted by Sutton in 1902

Identifying chromosomes

• number of chromosomes varies in different species

• # of chromosomes does not correlate with anything

• 46 chromosomes in humans (23 pairs)

• Each chromosome pair is named by a number, except…

Types of chromosomes

• ”Sex” chromosomes discovered by Morgan in 1908

• called ‘X’ and ‘Y’ chromosomes because of different shapes

• In humans and most animals • XX = female, XY = male

Types of chromosomes

• All the other chromosomes are called Autosomes,

• These are known by number only

Cell Divsion

A cell spends most of its life growing and maintaining its molecules and organelles.

Cells that divide must double their contents during this growth period, or they would

become progressively smaller over several divisions and eventually lose key

components. This growth period is called interphase, and it lasts from 10 hours to an

animal’s lifetime, depending upon the type of cell.

Because DNA is the hereditary material, its duplication is a critical interphase activity

for potentially dividing cells. In early interphase, called the G1 (“Gap 1”) phase of the

cell cycle, no DNA is made in most cells.Then suddenly, as if on cue, DNA synthesis

begins at several sites on each chromosome and continues for several hours, stopping

when a copy of each chromosome has been made. This period of DNA synthesis is

known as S phase, and although highly variable, it typically lasts about 8-10 hours.

Following the S phase, there is another gap period, the G2 Phase (yellow), in which proteins that have a role in cell division are produced. Some of these proteins cause the chromosomes to condense into compact units, while others are involved in the breakdown of the nuclear membrane.

The M phase (red) of the cell cycle consists of two processes; mitosis, or nuclear division, followed by cytokinesis, or cytoplasmic division. These processes occur in animals as they develop from fertilized eggs and as they replace worn out tissues.

Replication of chromosomes

• Replication of DNA = exact and complete duplication of original strand

• Replication proceeds at a replication fork along both ‘halves’ of the original

• Complementary strands are known as parent and daughter strands

Replicationof DNA

Mitosis

• Reproduction of a somatic cell is an exact duplication of the original

• ie. The daughter cells are exact clones

• They have the same # of chromosomes

• This # (different for each species) is known as the diploid number of chromosomes

• Somatic cells must be distinguished from sex cells , found only in testes or ovaries

Mitosis is a special kind of cell division used by

eukaryote cells. You will find a series of diagrams in

your text & notes which shows the stages of mitosis;

these are:* prophase* metaphase* anaphase* telophase

Mitosis is really a division of the nucleus into two

identical nuclei. It is followed by cytokinesis which is

the division of the cytoplasm into two.

interphaseinterphase

prophase

metaphaseanaphase

telophase

Phases of Mitosis

Prophase Metaphase

Anaphase Telophase

Late Telophase

A cell spends most of its life growing and maintaining its molecules and organelles.

Cells that divide must double their contents during this growth period, or they would

become progressively smaller over several divisions and eventually lose key

components. This growth period is called interphase, and it lasts from 10 hours to an

animal’s lifetime, depending upon the type of cell.

Interphase with symbolsfor chromosomes

Prophase with symbolsfor chromosomes

‘Prometaphase’ withsymbols for chromosomes

Metaphase with symbolsfor chromosomes

Anaphase with symbolsfor chromosomes

Telophase with symbolsfor chromosomes

Cytokinesis with symbolsfor chromosomes

Mitosis

MitosisAnimation

Mitosis animation U Ariz site: http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/mitosis_movie.html

Mitosis animation Cells Alive site:http://www.cellsalive.com/mitosis.htm

Mitosis-Meiosis Activity: http://biologyinmotion.com/cell_division/

Excellent Kean Univ Video of Overall Cell Cycle & Mitosis: http://www.kean.edu/~fglazer/PPT/ANIMS/lw04_cell_cycle_final.swf

Kean Univ Video on Meiosis: http://www.kean.edu/~fglazer/PPT/ANIMS/lw13_meiosis.swf

Paired chromatids

Chromosomal Replication

Meiosis

• Meiosis is the reproduction of sex cells (as opposed to somatic cells)

• This process occurs only in the testes or ovaries

• New cells (known as gametes) have only half the number of chromosomes of the parent cells

• This # (different for each species) is known as the haploid number of chromosomes

Mitosis

Meiosis I

Meiosis II

MeiosisAnimationwith crossing-over

Prophase 1 & Crossing over

Secondphaseof meiosis,yielding haploid gametes at bottom

Meiosis 1

PBS- Mitosis/meiosis side by side diagrams: http://www.pbs.org/wgbh/nova/baby/divi_text.html

Kean Univ Video on Meiosis: http://www.kean.edu/~fglazer/PPT/ANIMS/lw13_meiosis.swf

Mitosis-Meiosis Activity: http://biologyinmotion.com/cell_division/

Oncogenes are mutated forms of normal cellular genes involved in growth signalling pathways (proto-oncogenes). When these genes become mutated the cell does not require the presence of pro-growth signals (e.g. growth factors) in order to undergo cell division.

Tumour suppressor genes are genes often involved in the apoptotic pathway. Normally tumour suppressors detect breaks or defects in the DNA - if present in low concentrations these proteins will pause the cell cycle and active DNA repair mechanisms. If present in high concentrations, tumour suppressors shut down the cell cycle or cause apoptosis. When these genes are mutated to be dysfunctional then the cell does not undergo either of these events

The abnormal receptor on the right was coded for by an oncogene, it is no longer subject to the normal regulatory mechanisms of the organism

Chemotherapy & Side Effects

1.  Diagram A represents a cell from an organism with a diploid chromosome number of 10. Therefore, the diagram represents which one of the following stages?A. interphase of mitosisB. anaphase of mitosisC. metaphase I of meiosisD. prophase II of meiosisE. anaphase II of meiosis

2.  Diagram B represents a cell from an organism with a diploid chromosome number of 8. Therefore, the diagram represents which one of the following stages?A. prophase of mitosisB. metaphase of mitosisC. metaphase I of meiosisD. telophase I of meiosisE. metaphase II of meiosis

3. Diagram B represents a cell from an organism with a diploid chromosome number of 4. Therefore, the diagram represents which one of the following stages?A. prophase of mitosisB. metaphase of mitosisC. metaphase I of meiosisD. telophase I of meiosisE. metaphase II of meiosis

4. Diagram B represents a cell from an organism with a diploid chromosome number of 6.  Therefore, the diagram represents which one of the following stages?A. Prophase of mitosisB. Metaphase of mitosisC. Metaphase I of meiosisD. Telophase I of meiosisE. Metaphase II of meiosisF. None of the above

5.  Diagram C represents a cell from an organism with a diploid chromosome number of 6. Therefore, the diagram represents which one of the following stages?A. prophase of mitosisB. metaphase of mitosisC. metaphase I of meiosisD. prophase II of meiosisE. metaphase II of meiosis

6.  Diagram D represents a cell from an organism with a diploid chromosome number of 2. Therefore, the diagram represents which one of the following stages?A. prophase of mitosisB. prophase I of meiosisC. prophase II of meiosisD. metaphase of mitosisE. metaphase I of meiosisF. metaphase II of meiosis

ChromosomeSpread& Karyotype

Chromosomemodels