Cell Division Your body is composed of more than a billion cells

Why must cells divide? They are continually dying and must produce new cells An identical copy of your hereditary information is in the nucleus of each and every body cell called a somatic cell dbb.urmc.rochester.edu/.../photo_gallery.

Chromosomes The genetic information or blueprint that is organized into 46 chromosomes (each contains about one to two thousand genes) The genetic information or blueprint that is organized into 46 chromosomes (each contains about one to two thousand genes)

Karyotype Human chromosome number: 46 Karyotype – order of chromosomes from tallest to smallest.

Every time a cell divides it must copy the chromosomes Every time a cell divides it must copy the chromosomes

Goal of Mitosis is to allow for growth is to allow for growth maintain tissues maintain tissues Baby Grow to adult

Another way to look at this is like this: Another way to look at this is like this:

Stages of Mitosis is IPMAT Mitosis animation : hill.com/sites/ /student_view0/chapter2/animation__mitosis_and_cytokinesis.html

Interphase Time between divisions – cell spends 90% of its life here Time between divisions – cell spends 90% of its life here DNA is copied here DNA is copied here Typical human cell divides every 24 hours Typical human cell divides every 24 hours

Inside – looks like.. Diploid - 3 chromosome pairs, 6 individual chromosomes

Your nucleus initially contained six un- replicated chromosomes, and now it contains six replicated chromosomes. Your nucleus initially contained six un- replicated chromosomes, and now it contains six replicated chromosomes. The two identical copies of each chromosome are called sister chromatids The two identical copies of each chromosome are called sister chromatids They remain attached at a point called the centromere They remain attached at a point called the centromere

Prophase Chromosomes condense (are visible) Chromosomes condense (are visible) Sister chromatids pair up. Sister chromatids pair up. Nuclear membrane disappears Nuclear membrane disappears

Pro-metaphase-Start moving to sides

Metaphase Paired chromatids line up in the middle of cell Paired chromatids line up in the middle of cell

Anaphase Chromatids are pulled into the apart. They are dragged through the cytoplasm (V-shaped) Chromatids are pulled into the apart. They are dragged through the cytoplasm (V-shaped)

Telophase Daughter chromosomes reach the poles Daughter chromosomes reach the poles Cells start to separate Cells start to separate Nuclear membrane re-forms Nuclear membrane re-forms

Cytokinesis (Cell Cutting) The two daughter cells separate The two daughter cells separate

At the end of Mitosis, each daughter cell has an identical set of duplicate chromosomes At the end of Mitosis, each daughter cell has an identical set of duplicate chromosomes They are called Somates – body cells

Mitosis Stages Mitosis animation ations/content/mitosis.h tml ations/content/mitosis.h tml ations/content/mitosis.h tml

Interphase is subdivided G1 – Gap 1 or growth 1  cell carries out normal functions G1 is a period of activity in which cells do most of their growing, increasing in size and synthesizing new proteins and organelles

S Synthesis – DNA is copied to prepare to divide it synthesizes (to make) a duplicate set of DNA it synthesizes (to make) a duplicate set of DNA

G2 G2 – Gap 2  is where the organelles and molecules required for cell division are produced.

M phase then Cytokinesis Mitosis takes about an hour (most time spent during G1, S and G2 phase) Mitosis takes about an hour (most time spent during G1, S and G2 phase)PMAT

Check points G1 – Checks DNA damage before begins replication (S phase), if damaged then repaired or self destructs if cannot repair. G1 – Checks DNA damage before begins replication (S phase), if damaged then repaired or self destructs if cannot repair. G2 – Checks DNA to see if properly copied during S phase G2 – Checks DNA to see if properly copied during S phase M – checks to ensure spindle fibers attach properly during metaphase M – checks to ensure spindle fibers attach properly during metaphase

How does Mitosis lead to Caner? Cancer is basically a disease of mitosis What is happening? The normal checkpoints that regulate mitosis are ignored or overridden by cancer cell.

How does it occur? a change in function or a DNA mutation occurs in one of several genes (proteins) that normally function to control growth a change in function or a DNA mutation occurs in one of several genes (proteins) that normally function to control growth

Result Once these crucial Cell Cycle genes start behaving abnormally, cancer cells start to proliferate wildly by repeated, uncontrolled mitosis Tumor production: hDsok&feature=related hDsok&feature=related hDsok&feature=related

Examples: (1) p53 protein can senses DNA damage and halts progression of cell cycle. Also known as tumor suppressor gene. However, p53 is mutated in over 50% of all human cancers.

(1) BRCA 1 gene, the "Breast Cancer Gene" normally repairs mutations in PTEN gene which suppress tumor formation BRCA 1 gene BRCA 1 gene but if a gene contains mutations such that BRCA1 does not work properly, tumor formation can begin

Meiosis Cell Division to make sex cells (sperm and eggs) Cell Division to make sex cells (sperm and eggs) Chromosome number is halved creating these cells Chromosome number is halved creating these cells ex. 46  23 ex. 46  23 Meiosis animation: om/webcontent/animatio ns/content/meiosis.html om/webcontent/animatio ns/content/meiosis.html om/webcontent/animatio ns/content/meiosis.html

Diploid vs. Haploid Diploid – two or a pair of chromosome Haploid – 1 set of chromosomes Examples: Diploid = 2 48 Haploid = 1 24 YOU TRY: If the diploid chromosome number is 28, what is the haploid number?

Stages : IPMAT then PMAT II Crossing Over (independent Assortment) - tetrad

Crossing Over Homologous chromosomes can swap information, increasing variability in offspring Homologous chromosomes can swap information, increasing variability in offspring Takes place in prophase Takes place in prophase Tetrad – set of 4 chromosomes

Homologous Chromosomes The two versions of each chromosome The two versions of each chromosome One from mom, one from dad One from mom, one from dad

Gametes Gametes are sex cells SpermEgg Each are haploid – half the number of original set of chromosomes Diploid = 46 Haploid = 23

Spermatogenesis Creates four functional sperm cells Creates four functional sperm cells

Oogenesis Creates one functional Ovum (egg) and 3 polar bodies Creates one functional Ovum (egg) and 3 polar bodies

Gametes – sex cells Products of meiosis in males formed in testes? A: 4 sperm A: 4 sperm Products of meiosis in females formed in ovaries? A: 1 functional egg (the other 3 cells are not functional and are reabsorbed by the body? Humans have 46 homologous chromosomes (23 pairs)

Stages of Meiosis Interphase: same as Mitosis Prophase 1: Same except for Crossing - over can occur – leads to independent assortment (life is a box of chocolates) Metaphase 1: Same except that form a tetrad Homologous chromosomes that align at the equatorial plate. Anaphase 1: Same except that the Homologous pairs separate with sister chromatids remaining together. Telophase 1: Same except each daughter contains only one chromosome of the homologous pair (not a pair of chromosomse).

Second Stage Prophase 2: same as mitosis Metaphase 2: same as mitosis Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole. (same as mitosis) Telophase 2: Four haploid daughter cells instead of two.. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.

Timing in Meiosis When do Females produce their eggs? Prior to birth Prior to birth What do Males produce sperm? Once hit puberty Once hit puberty Helpful saying I don’t use “Mi-Toes-es” for making sperm or eggs! Helpful saying I don’t use “Mi-Toes-es” for making sperm or eggs!

Differences between Mitosis and Meiosis MitosisMeiosis IPMATIPMAT I & PMAT II DiploidHaploid SomateGamete 2 cells4 cells

Non-Disjunction- when chromosomes do not separate correctly during meiosis. Non-Disjunction- when chromosomes do not separate correctly during meiosis. End up with 47 or 45 in each new cell. End up with 47 or 45 in each new cell. Example: Downs Syndrome = Trisomy 21 (3 chromosomes 21) Turner’s Syndrome = one X and no second sex chromosome

Trisomy 21