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Genetics
Why do we look the way we do?
Inheritance of chromosomes
• Egg + sperm  zygote
egg
zygote
sperm
How does this work?
• Paired chromosomes have ___________________
– but __________________________
eye
color
(blue?)
hair
color
eye
color
(brown?)
hair
color
What did we show here?
• Genes come in “versions”
– brown vs. blue eye color
– ___________________
• Alleles are inherited separately from each parent
– brown & blue eye colors are separate & do not blend
• either have brown or blue eyes, not a blend
• Some alleles mask others
– brown eye color masked blue
Traits are inherited as separate units
• For each trait, an organism inherits
_________________________________________
– a __________________ organism inherits
1 set of chromosomes from each parent
• __________________________________
1 from Mom
1 from Dad
Making gametes
BB = brown eyes
bb = blues eyes
Bb = brown eyes
B
BB
B
b
bb
b
B
Bb
Remember meiosis!
b
How do we say it?
B
BB
B
BB = brown eyes
bb = blues eyes
b
bb
b
B
Bb
Bb = brown eyes
b
Punnett squares
x
Bb
male / sperm
X
female / eggs
Bb
B
b
BB
Bb
Bb
bb
B
b
Genetics vs. appearance
• There can be a difference between how an organism looks &
its genetics
– appearance or trait = ________________
• brown eyes vs. blue eyes
– genetic makeup = _________________
• BB, Bb, bb
2 people can have the same appearance but
have different genetics:
Genetics vs. appearance
How were these
brown eyes made?
eye
color
(brown)
eye
color
(brown)
eye
color
(brown)
eye
color
(blue)
vs.
B
BB
B
Bb
B
b
Meiosis
Homologous Chromosomes
• Chromosomes that have a
corresponding partner
from each parent.
Paired chromosomes
• Homologous chromosomes
– both chromosomes of a pair carry ________________
• control same inherited characters
• ____________________________________
diploid
2n
2n = 4
eye color
(brown?)
eye color
(blue?)
homologous
chromosomes
double stranded
homologous chromosomes
Cell division / Asexual reproduction
• Mitosis
– produce cells with __________________
• identical daughter cells
– ___________________
• clones
– ____________________________
• same genetic information
Aaaargh!
I’m seeing
double!
Asexual reproduction
• Single-celled eukaryotes
– yeast
– Paramecium
– Amoeba
• Simple multicellular eukaryotes
– Hydra
• budding
What are the
disadvantages of
asexual reproduction?
What are the
advantages?
Haploid vs. Diploid
• A cell that contains only one set of chromosomes is
_________________________
• A cell that contains both sets of homologous
chromosomes is ________________________
How about the rest of us?
• What if a complex multicellular organism (like us) wants to
reproduce?
– joining of egg + sperm
• Do we make egg & sperm by mitosis?
What if we did, then….
 
46
egg
+
46
92
sperm
zygote
Meiosis
Goal: Reduce genetic material by half
Why?
from mom
from dad
meiosis reduces numbers
of chromosomes by half
child
How do we make sperm & eggs?
• Must reduce 46 chromosomes  23
– must ______________ the number of chromosomes
– ______________
46
23
zygote
23
46
egg
23
46
23
sperm
gametes
Meiosis makes sperm & eggs
• 46 chromosomes to 23 chromosomes
– half the number of chromosomes
46
23
egg
46
23
sperm
Meiosis = reduction division
• Meiosis
– special cell division in sexually reproducing organisms
– _______________________________
• _________________
• _________________
– half
– makes _____________
• sperm, eggs
Meiosis: two cell divisions
homologous
Chromosomes separate
Sister
chromatids
separate
Result: ONLY one copy of each chromosome in a gamete.
Meiosis 1 overview
double
stranded
Divide 1
• 1st division of meiosis
Line Up 1
prophase 1
metaphase 1
telophase 1
gamete
Meiosis I : the reduction division (2n
Prophase I
(early)
(diploid)
Prophase I
(late)
(diploid)
Metaphase I
(diploid)
Anaphase I
(haploid)
n)
Telophase I
(haploid)
Homologous chromosomes___________
__________________________
.
Crossing over creates ____________
Meiosis II
Gene X
Meiosis II produces gametes with one copy of each chromosome
(thus one copy of each gene)
Bye Bye 2
Meiosis 2 overview
telophase 2
telophase 1
Line Up 2
metaphase 2
4
Meiosis II : the equal division
Prophase II
(haploid x 2)
Metaphase II
(haploid x 2)
Anaphase II
(haploid)
Telophase II
(haploid)
Sperm and Egg formation
The value of meiosis 1
• Consistency over time
– meiosis __________________________________________ from
generation to generation
from Mom
Mom
Dad
offspring
from Dad
We’re
The value of meiosis 2mixing things
up here!
• Change over time
– meiosis _______________________________
• gametes of offspring do not have
same genes as gametes from parents
• new combinations of traits
from Dad
from Mom
offspring
How does this explain:
family resemblance & differences!
Why are the kids so similar to
the parents but
exact?
not
Michael & Kirk
Douglas
Baldwin brothers
Martin & Charlie Sheen, Emilio Estevez
“Putting It All Together” - Fertilization
Putting it all together…
gametes
46
23
23
egg
23
46
23
sperm
46
46 46
46 46 46
46
46
46
zygote
What Meiosis is About
Meiosis allows the creation of unique individuals
through sexual reproduction.
Meiosis & mitosis
• Meiosis to make
gametes
– ___________________
• Mitosis to make copies
of cells
– __________
– __________
– __________
MITOSIS
MEIOSIS
Produces cells for repair,
maintenance, growth,
asexual reproduction
Only produces gametessex cells (egg/sperm)
Results in
Reduction division results
in
Mitosis
# of divisions
# of daughter cells
Genetically identical?
Chromosome #
Where
When
Role
Meiosis