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2006-2007
Biology is the only subject in which
multiplication is the same thing as division…
2006-2007
Making New CellsMaking New DNA
Where it all began…You started as a cell smaller than a period at the end of a sentence…
And now look at you…
How did you get from there to here?
• Going from egg to baby…. the original fertilized egg has to divide…
and divide…and divide…
and divide…
Getting from there to here…
Why do cells divide…
amoeba
starfish
Reproduction
Growth & Development
Repair
What must be copied in order for a cell to divide?
animal cellplant cell
Copying DNAA dividing cell
duplicates its DNA.
But what is DNA?
Isn’t a gene, chromosome and DNA all interchangeable?
AA
A
A
TC
G
CG
TG
C
T
Each gene codes for a particular protein
CELL CYCLE
Growth(in size)
Synthesis(Replicate DNA)
Growth(in organelles)
Mitosis: Cell Division
• Humans have 46 chromosomes.• That is 46 individual strands of DNA.
Chromosomes of Human Female
46 chromosomes23 pairs
Karyotyping
Chromosomes of Human Male
46 chromosomes23 pairs
Karyotyping
Homologous chromosomesHomo=sameOne from each parent
Why are chromosomes paired?
Similar in size, shape and genetic content
The only difference between living organisms is the amount and order of the DNA alphabet.
Where do you find DNA?
DNA: deoxyribonucleic acid
England 1953
James Watson and Francis Crick
http://bioweb.wku.edu/asp/bisc/images/WatsonCrick.jpg
Structure of DNA
Monomer: NUCLEOTIDEMade of 3 parts
Deoxyribose/
A = AdenineT = ThymineC = CytosineG = Guanine
phosphate
sugar N base
phosphate
sugar N base
phosphate
sugar N base
phosphate
sugar N base
strong bonds
POLYMER: DNA
SHAPE: Double Helix
DNA Structure
weak HYDROGEN bonds between nitrogen bases join the 2 strands
Why do the bonds have to be weak?
A pairs with T C pairs with GA - T C - G
REPLICATION OF CELLS & DNA
Shape of DNA
Why does DNA Replicate?
Cell Reproduction
Helicase
What enzymes are used?
Newly copied strands of DNA
How does DNA replicate?
Polymerase
MITOSIS: Asexual ReproductionCell Division
• Creating 2 new identical cells
CELL CYCLE
Growth(in size)
Synthesis(Replicate DNA)
Growth(in organelles)
Mitosis: Cell Division
Interphase = G1, S & G2
Copying DNA for Mitosis
What does the DNA look like?
What would happen if you tried to copy it now?
nucleus
cell
DNA
Organizing & packaging DNA
nucleus
cell
DNA
nucleus
cell
How many chromosomesin this organism?
DNA has been “wound up”
MITOSIS
DNA Replication
End Result
2 IDENTICALDAUGHTER CELLS
Plant vs. Animal Mitosis
ANIMALCytokinesis: splitting
of the cells
PLANTCell Plate: cuts cell
wall in half
How about the rest of us?• What if a complex multicellular organism (like us)
wants to reproduce?• Do we make egg & sperm by mitosis?
46 46+ 92
egg sperm zygote
What if we did, then….
Doesn’t work!
No!
2006-2007
Meiosis &Sexual Reproduction
MEIOSIS
Human female karyotype
46 chromosomes23 pairs
XX
diploid = 2 copies 2n
46 chromosomes23 pairs
XY
Human male karyotypediploid = 2 copies 2n
Meiosis makes sperm & eggs• 46 chromosomes to 23 chromosomes
23
2346
egg
sperm
46
meiosis
haploiddiploid
Meiosis & Mitosis
• Meiosis to make gametes
• Mitosis to make copies of cells: growth, repair, development
mitosiszygote
Putting it all together…
23
2346
egg
sperm
46
meiosis 4623
23
fertilization mitosis &development
meiosis fertilization mitosis + development
46
46
46
46
46
4646 46
gametes
Meiosis introduces genetic variation• gametes of offspring do not have
same genes as gametes from parents• new combinations of traits
from Mom
from Dad
new gametes made by offspring
offspring
We’remixing thingsup here!
variation
Why are red hair and freckles usually inherited together?
Red Hair
Freckles
And sometimes not?
Crossing over
Red HairBrown Hair
No Freckles
Freckles
RedHair
No Freckles
Non-disjunction• Sometimes the chromosomes don’t split
properly• Some cells have extras, some with less
Any Questions??
What are theDISadvantages ofasexual reproduction?
What are theDISadvantages ofsexual reproduction?
What are theadvantages ofsexual reproduction?
What are theadvantages ofasexual reproduction?
Cancer
Gametogenesis in Humans
