CHROMOSOMES AND CELL REPRODUCTION

Section I Chromosomes Formation of New Cells by Cell Division New cells are formed when old cells divide. 1. Cell division is the same as cell reproduction. 2. The type of cell division differs depending on the organism. .

Prokaryotic cells, like Bacteria reproduce by binary fission. Binary fission: asexual/ a single parent passes exact copies of its DNA to its offspring 1st stage: DNA is copied 2nd stage: Cell divides

Eukaryotic cells reproduce by another type of cell division- MITOSIS 1st stage: DNA is copied chromatids: 2 exact copies of DNA that make up a chromosome centromere: point of attachment of 2 chromatids 2nd Stage: DNA and protein coil into chromosomes

Draw and Label a chromosome:

The chromatids separate during cell division and are each placed into a new cell. This ensures that each cell has the same genetic information as the original cell. When a cell divides: the DNA is copied 1st and then distributed. Each cell ends up with a complete set of the DNA.

Gamete cells- which are sperm and egg are created through another type of cell division-MEIOSIS Egg cell surrounded by sperm cells.

II. Chromosome Number and Structure Humans have 46 chromosomes (23 Pairs) in somatic cells. Somatic cells: All body cells (except sex cells) Gametes: sex cells (sperm and eggs) Chromosomes differ in size, shape and set of genes.

Sets of Chromosomes Homologous chromosomes are those that are paired together and are similar in size, shape and genetic content. 46 chromosomes = 2 sets of 23

Diploid- cell contains 2 sets of chromosomes Haploid- cell contains 1 set of chromosomes The fusion of 2 haploid cells forms a diploid zygote. Zygote-fertilized egg cell

XX = Female XY = Male B. Sex Chromosomes Out of 23 pairs of chromosomes- 22 pairs are autosomes; 1 pair are sex chromosomes. Sex chromosomes are the X and Y. Male Sperm determines the sex of a child. XX = Female XY = Male

C. Change in Chromosome Number There are 1000’s of genes on each of our chromosomes. The presence of all 46 chromosomes is essential for normal development and function. Trisomy- having an extra copy of a chromosome Example: Trisomy 21- Down’s Syndrome Cause of Trisomy is NONDISJUNCTION. This is when the chromosomes don’t separate and one gamete ends up with 2 chromosomes.

Mikey has Down’s Syndrome. He has an extra chromosome Mikey has Down’s Syndrome. He has an extra chromosome. Instead of having a pair of # 21 chromosomes, he as 3 copies of it.

Karyotype: Normal vs Down’s Syndrome

D. Change in Chromosome Structure- MUTATIONS Types of Mutations: 1. Deletion- piece of chromosome breaks off 2. Duplication- extra chromosome fragment attaches; 2 copies of certain genes 3. Inversion- chromosome attaches in reverse order 4. Translocation – chromosome piece attaches to a nonhomologous chromosome

See p 124 Draw these Chromosomal Mutations

Section II- The Cell Cycle A. Cell cycle-Cellular growth and division 90% of the time is spent in Interphase. (preparation to divide) The cell will enter the last 2 phases of the cell cycle only if it is about to divide.

5 Phases of the Cell Cycle The 1st 3 stages are part of Interphase. 1. 1st Growth (G1)-Grows rapidly (nerve cells stay in this stage) 2. Synthesis- DNA is copied; each chromosome is copied 3. 2nd Growth (G2)- Growth; prep for division; microtubules are assembled 4. Mitosis- nucleus divides into 2 nuclei (2 cells) that are identical 5. Cytokinesis- cytoplasm divides

Mitosis and cytokinesis produce new cells that are identical to the original cells and allow organisms to grow, replace damaged tissue, and in some organisms, reproduce.

B. How do cells “know” when to divide? “Red light- Green light” The cell cycle in eukaryotes is controlled by many proteins. 1.Cell growth check point(G1): makes decision whether cell will divide 2. DNA synthesis checkpoint (G2): protein triggers mitosis and cell begins many processes needed to proceed into mitosis 3. Mitosis checkpoint: triggers the exit from mitosis; It signals the beginning of G1.

CANCER- Uncontrolled growth of cells It is essentially a disorder of cell division. Cancer cells do not respond normally to the body’s control mechanisms Some Mutations cause cancer by over-producing growth-promoting molecules, thus speeding up the cell cycle or by inactivating the control proteins that normally act to slow or stop the cell cycle.

Section III Mitosis and Cytokinesis 4 stages of Mitosis: 1. Prophase 2.Metaphase 3. Anaphase 4. Telophase

Prophase: Chromosomes become visible, the nuclear envelope dissolves and the spindle forms. What makes up the spindles? It is made up of centrioles & individual microtubule fibers; they are involved in moving the chromosomes.

Metaphase Chromosomes line up in the Middle (middle phase)

Anaphase Centromeres divide, chromatids move toward opposite poles.

Telophase Nuclear envelope reforms at each pole, chromosomes uncoil , spindle divides. Mitosis is complete and cytokinesis begins.

Cytokinesis Cytoplasm divides in half, and the membrane grows to enclose each cell, 2 separate cells are formed.

A Difference in Plant Cells A cell plate forms across the middle of the plant cell. A new cell wall forms on both sides of the cell plate.

Put the following in the correct order Put the following pictures in the correct order as they occur during mitosis: Answer: c,b,d,a