Genes and Chromosomes• Humans have 46 chromosomes in all

body cells called SOMATIC CELLSCELLS THAT ARE NOT BODY CELLS ARE

SEX CELLS = GAMETES

• You have 23 pairs of chromosomes ---each pair is called HOMOLOGOUS

• In Homologous pairs each has one copy of the same characteristic One from mom and one from dad (example eye color, skin tone etc.)

What is a gene?

• Characteristics are forms of genes• Genes are a segment that codes for

a trait• Traits can be….

– Eyecolor– Hair color

Chromosome NumbersPlants Mammals Reptiles14- cucumber 40- beaver 36- boa constrictor40- peanut 38- domestic cat 22- American Toad24- pine tree 78- dog48- potato48- chimpanzeeFish80- sugar cane 56- elephant 46- small-mouth bass

30- giraffe 84- troutBirds 64- horse80- canary 60- cattle Insects68- dove 32- walrus 6- mosquito80- duck 44- killer whale32- honey bee78- raven 8- 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

–10 % of time doing cell DIVISION •Cells with either divide by MITOSIS or MEIOSIS

•Mitosis is for –repair, maintenance, and growth

•Meiosis is for –reproduction to produce sex cells

Before ANY division, each chromosome is copied exactly—during S phase of

INTERPHASE

•Before ANY division, each chromosome is copied exactly—during S phase of INTERPHASE

Lets look at one way cells divide

Mitosis: Nuclear division resulting in

two identical sets of

chromosomes

Phases of Mitosis

1- Prophase2- Metaphase3- Anaphase4- Telophase

Stages of Mitosis• Prophase

1. Chromosomes become visible (coil up and get shorter and thicker) CHROMATINCHROMATID

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

• Telophase1. Nuclear membrane appears

around each set of chromosomes

2. Chromosomes unwind and go back to being chromatin

CYTOKINESIS

CYTOKINESIS• Cell membrane begins to pinch

inward (furrowing)• Entire cell divides in half• Each daughter cell has…

– an exact duplicate of the DNA– 46 chromosomes– 23 pairs of chromosomes

• Mitosis video (7 min)

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: interphase2: late interphase /

beginning prophase3: early prophase4: mid prophase5: late prophase

6: metaphase7: late metaphase / early anaphase8: anaphase9: early telophase10: late telophase / cytokinesis

VOCABULARY TERMS

InterphaseChromatinReplicationDaughter cellsMitosisCytokinesis

SomaticHomologousDiploidCentromereGeneChromatidChromosome