Genes and Chromosomes Humans have 46 chromosomes in all body cells (not sex cells) ---called SOMATIC CELLS You have 23 pairs of chromosomes ---each pair is called HOMOLOGOUS Each chromosome in the homologous pair contains genes that affect the same characteristic (example eye color, skin tone etc.)

Chromosome Numbers PlantsMammalsReptiles 14- cucumber40- beaver36- boa constrictor 40- peanut38- domestic cat22- American Toad 24- pine tree78- dog 48- potato48- chimpanzeeFish 80- sugar cane56- elephant46- small-mouth bass 30- giraffe84- trout Birds64- horse 80- canary60- cattleInsects 68- dove32- walrus6- mosquito 80- duck44- killer whale32- honey bee 78- raven8- drosophila (fruit fly) 446- butterfly

Anatomy of a Chromosome

How does 6 feet of DNA fit into each nucleus of each cell?? Video clip: How DNA is Packaged

Check your Understanding How many chromosomes do human cells have? How many pairs of chromosomes do human cells have? What are somatic cells? You have one gene for blue eyes and one gene for brown eyes. –Where did these genes come from? What are the two halves of a single chromosome called? What structure holds the chromatids together? What is a gene?

Cell Cycle Cell spends… –90% of time in INTERPHASE – doing the job it is programed for DNA is stretched out into long, thin chromatin strands so it can be utilized –10 % of time doing cell DIVISION Before division, each chromosome is copied exactly—S phase replication Nucleus divides and each daughter cell gets a full set of chromosomes

video clip: eukaryotic cell cycle cell cycle animation

Lets look at one way cells divide Mitosis: Nuclear division resulting in two identical sets of chromosomes

Phases of Mitosis 1- Prophase 2- Metaphase 3- Anaphase 4- Telophase

Stages of Mitosis Prophase 1.Chromosomes become visible (coil up and get shorter and thicker) CHROMATIN  CHROMATID 2. Nuclear membrane disintegrates (disappears) 3. Centrioles move to opposite sides of the cell 4. Spindle fibers appear and shoot out from centrioles (longest phase)

Metaphase 1. Chromosomes migrate to equator Centromeres align along center 2. Spindle fibers attach to each chromosome

Anaphase 1.Sister chromatids are pulled apart 2. Separate chromatids are pulled to opposite sides of the cell by spindle fibers

Telophase 1.Nuclear membrane appears around each set of chromosomes 2. Chromosomes unwind and go back to being chromatin

CYTOKINESIS Entire cell divides in half Each daughter cell has… – an exact duplicate of the DNA –46 chromosomes –23 pairs of chromosomes (diploid)

Check your Understanding How are the terms DNA, chromatin, chromosome, and genes related? What is the name of the process by which DNA is copied? Name, in order, the 6 stages of the cell cycle, starting with the phase cells are in most of the time Name the phase of the cell cycle where: –Chromosomes line up in the middle of the cell –Chromosomes first become visible –Spindle fibers first appear –Spindle fibers attach to sister chromatids –Centrioles move to opposite sides of the cell –Sister chromatids get pulled apart

Still checking… –Nuclear membrane disappears –Nuclear membrane reappears –Entire cell divides in half –No chromosomes are visible How many daughter cells are created from one parent cell? –How many chromosomes does each daughter cell have? –How many pairs of chromosomes does each daughter cell have? –What is the ploidy of the daughter cells?

1: interphase 2: late interphase / beginning prophase 3: early prophase 4: mid prophase 5: late prophase 6: metaphase 7: late metaphase / early anaphase 8: anaphase 9: early telophase 10: late telophase / cytokinesis

VOCABULARY TERMS Interphase Chromatin Replication Daughter cells Mitosis Cytokinesis Somatic Homologous Diploid Centromere Gene Chromatid Chromosome