Cell Division: MITOSIS

Genes and Chromosomes

• Humans have 46 chromosomes in all body cells (somatic cells)

• You have 23 pairs of homologous chromosomes– The two chromosomes in the pair look similar

and contain genes which affect the same characteristics (2 different alleles)

• All of your somatic cells are diploid—they have chromosomes which are in homologous pairs

• Some cells don’t have any DNA at all– Red blood cells

Anatomy of a Chromosome

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 2 forms of this gene called?

• What does diploid mean?• What are the two halves of a single chromosome called?• What structure holds the chromatids together?• What is a gene?

How Eukaryotic Cells Divide

• Cell spends most of its time in interphase –not dividing, just doing its job– DNA is stretched out into long, thin chromatin

strands

• Before division, each chromosome is copied exactly—replication

• Nucleus divides and each daughter cell gets a full set of chromosomes– This is called mitosis

Stages of Mitosis

• Prophase– Chromosomes become visible as they coil up

and get shorter and thicker– Nuclear membrane disappears– Centrioles move to opposite sides of the cell– Spindle fibers appear and shoot out from

centrioles

• Metaphase– Chromosomes line up in center of cell– Spindle fibers attach to each chromosome

• Anaphase– Sister chromatids are pulled apart– Chromatids are reeled to opposite sides of the

cell by spindle fibers

• Telophase– Nuclear membrane appears around each set

of chromosomes– Chromosomes unwind and go back to being

chromatin

Cytokinesis

• Whole cell divides in half

• Each daughter cell has an exact duplicate of the DNA

• Each daughter cell has 46 chromosomes

• Each daughter cell is diploid—23 pairs of chromosomes

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

Interphase

Chromatin

Replication

Daughter cells

Mitosis

cytokinesis

SomaticHomologousAllelesDiploidCentromereGeneChromatidchromosome