Standard 2 Cell Division “Chromosome Waltz”

Chromosome Condensed form of chromatin a threadlike structure of nucleic acids and protein Always paired with an identical copy of itself

CHROMATID Chromosome SISTER CHROMATIDS

Chromosome

Types of Chromosomes Y X Autosomes The 1st 22 pairs of Chromosomes in humans. Sex Chromosomes 23rd pair In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome. The Y chromosome is what makes a baby boy. X Y

Types of Cell Division Asexual: Offspring are identical to parents Examples: Budding: yeast Binary Fission: bacteria Sexual: Offspring have a combination of genetic information from 2 parents (Sperm and Egg) Ex: Animals and Plants

Why do cells divide? Growth Reproduction (Development) Repair or Replace

What Happens in Cell Division Replicates the DNA exactly. Movement of the two copies of DNA to opposite ends of the cell. Separates into two daughter cells.

Mitosis (1 cell becomes 2) both new cells are identical to the original (all cells except sperm & eggs do this)

Cell Cycle Interphase 90% of cell cycle Three phases G1- Growth Chromosomes appear as threadlike coils (chromatin) 90% of cell cycle Three phases G1- Growth S- DNA Replication G2- Growth (prepares to divide)

Mitosis 4 stages Prophase Metaphase Anaphase Telophase PMAT Cell division occurs in a series of stages, or phases. 4 stages Prophase Metaphase Anaphase Telophase PMAT

Prophase "BEFORE" Mitosis begins (cell begins to divide) You can see chromosomes start to form Late Early

Chromosomes line up in the center of the cell Metaphase "MIDDLE" Chromosomes line up in the center of the cell

Anaphase "ANTI" Chromatids or chromosomes separate and begin to move to opposite ends of the cell

Chromosomes appear as chromatin Mitosis ends Telophase "TWO" Two new nuclei form Chromosomes appear as chromatin Mitosis ends

Cytokinesis Become two identical new cells "Split" Become two identical new cells Half the size of the original

Metaphase Interphase Prophase Anaphase Telophase What Stages of Mitosis can you find?

Mitosis Meiosis What looks similar between mitosis and meiosis? What looks different? Prophase Interphase Mitosis Cytokinesis Telophase Metaphase Anaphase Meiosis

Meiosis- The process in which gametes (sex cells) are made.

1 cell becomes 4 cells called gametes Meiosis 1 cell becomes 4 cells called gametes Male gametes = Sperm Female gametes = Eggs

Cells in your body include… Somatic cells: Make up the various parts of your body including tissues and organs. Diploid cells (Full set of 23 chromosome pairs) Gametes: sex cells – eggs in females and sperm in males. Haploid cells (1/2 required # chromosomes)

Meiosis is Mitosis twice The Difference? Meiosis is Mitosis twice without Interphase in between & Mitosis is in my Toes, but Meiosis is in my Ovaries

Why Meiosis? Number of Fertilization Chromosomes Union of sperm and egg (n) Zygote is formed (2n) The chromosome number is reduced, so at fertilization there is the correct # of chromosomes.

Why meiosis? Cuts chromosome # in half Creates variation for Evolution Makes offspring unique

Meiosis creates variation in 3 ways 1) Law of Segregation chromosome pairs separate during meiosis 2) Law of independent assortment genes are separated randomly (shuffle) 3) Crossing Over chromosome parts break off & reattach to other chromosomes creates new chromosome

Mitosis (1 cell becomes 2) both new cells are identical to the original (all cells except sperm & eggs do this)

1 cell becomes 4 cells called gametes In Meiosis… 1 cell becomes 4 cells called gametes Male gametes = Sperm Female gametes = Eggs Mitosis is in my Toes, but Meiosis is in my Ovaries

Mitosis or Meiosis Haploid (N) Diploid (2N) Cells with 2 full sets of genetic info Human body cells have 46 chromosomes each (diploid or 2N # is 46) Haploid (N) Cells with 1 set of genetic info Human sperm & eggs have 23 chromosomes (haploid or N # is 23)

Meiosis Mitosis Makes haploid cells Makes diploid cells Why ---Importance: Meiosis Makes haploid cells Makes genetically different cells Takes place at certain times Males: after puberty Females: Before birth Mitosis Makes diploid cells All cells identical Involved in somatic cell reproduction. Happens ALL your life

Stages of Meiosis Interphase Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II

Interphase Interphase is the same as Mitosis. G1, S phase and G2.

Prophase I Same as Mitosis…except: Each pair of sister chromosomes matches with another set of sister chromosomes. Forms a tetrad- 2 sets of chromosomes (4 chromatids). This step is when crossing over occurs!!!!

Metaphase I The tetrads line up at the center of the cell.

Anaphase I Tetrads separate into chromosomes and move to opposite ends of the cell.

Telophase I The chromosomes uncoil and the cell begins to break into two cells. Still too many chromosomes, so the cells goes through another 4 stages.

STOP!! There is NO interphase II in meiosis… Why?? No need to replicate the DNA again…. We’re making haploid cells with only HALF the required DNA.

Prophase II Chromosomes coil and thicken. Nuclear envelopes break down.

Metaphase II Chromosomes line up at the center of the cell.

Anaphase II Chromosomes separate and the chromatids move to opposite ends of the cell.

Telophase II The chromatids uncoil and lengthen, and the cell breaks into two cells. Four gametes have been made They are haploid cells (half necessary DNA).

Meiosis Anaphase 1 Anaphase 2 Interphase (approx 90% of time) DNA Replication Prophase 1 Tetrad forms Crossing over occurs Metaphase 1 Chromosomes move to midline Anaphase 1 Homologous chromosomes separate Anaphase 2 Sister chromatids separate The Rest is Just Like Mitosis!

Chromosomes How do we look at the chromosomes of an individual? The collection of chromosomes found in an individual’s cells Karyotype

Chromosomes How is it made? Chemically treat and stain chromosomes in cells from a blood sample The chromosomes are then photographed, cut out, arranged in pairs from largest to smallest, and numbered

Chromatin Chromosome Scatter Karyotype

Chromosomes Abnormalities Nondisjunction (NOT-COMING-APART) Chromosomes fail to separate during anaphase 2. Mutations: changes in Chromosome Structure

Nodisjunctions What if a chromosome is missing? Most do not survive to be born If a chromosome is missing the condition is called Monosomy EX: Turners (XO)

Nondisjunctions What if a cell has an extra chromosome? The condition in which a cell has an extra chromosome is called Trisomy Example: Trisomy 21 (Down Syndrome)

Chromatids do not Separate in Anaphase II Nondisjunction TRISOMY MONOSOMY NORMAL X x l Chromatids do not Separate in Anaphase II

Mutations Deletion part of the chromosome breaks off Duplication: part of the chromosome is repeated

Cancer Mutations in genes that control normal cell division can lead to cancer. Increasing your risk Sun without sun block Smoking or being around 2nd hand smoke Working with known cancer causing chemicals.

Proto-Oncogenes are normal genes that code proteins involved in a cell's normal growth Oncogenes tell cells to make proteins that cause excessive cell growth and division. *Oncogenes are Mutant Forms of Proto-Oncogenes*

Why don’t we all get cancer? Tumor Suppressor Genes Normal genes whose ABSENCE can lead to cancer. Why don’t we all get cancer? Genes come in pairs, one from each parent A defect in one copy will not cause cancer because the other normal copy is still functional.