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Genes and Chromosomes
• Humans have 46 chromosomes in all body
cells called SOMATIC CELLS
CELLS 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 Numbers
Plants
14- cucumber
40- peanut
24- pine tree
48- potato
80- sugar cane
Birds
80- canary
68- dove
80- duck
78- raven
Mammals
40- beaver
38- domestic cat
78- dog
48- chimpanzee
56- elephant
30- giraffe
64- horse
60- cattle
32- walrus
44- killer whale
Reptiles
36- boa constrictor
22- American Toad
Fish
46- small-mouth bass
84- trout
Insects
6- mosquito
32- honey bee
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- 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
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: 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
Somatic
Homologous
Diploid
Centromere
Gene
Chromatid
Chromosome
Interphase
Chromatin
Replication
Daughter cells
Mitosis
Cytokinesis