Download PPT- Genetics

Mendel and His Discoveries
Chapter 11
Gregor Mendel

Gregor Mendel (1822-1884)
Experimented with pea plants and
developed fundamental rules of
genetics and patterns of
inheritance.
Punnett Squares
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Crosses between parents that differ
in only one trait are called
MONOHYBRID CROSSES.
P= Parents
F1= First Filial generation (kids)
F2= Second Filial generation
(grandkids)
Mendel and Pea Plants
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For his plant experiment he crossed
a tall plant with a short plant.
All of the offspring looked tall.
Why?
Because the tall plants had a
dominant trait and the short plants
had a recessive trait.
Alleles

Alleles are simply versions of genes
THE ALLELES FOR
COW FUR COLOR
ARE BLACK.
BROWN, AND
WHITE
Prediction of Genetic Crosses
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The alleles for tallness of a plant:
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TT= Dominant (Tall)
tt= Recessive (Short)
How do we know for sure that they
would all be tall?
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The Punnet Square
Punnett Squares
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Tool to predict outcomes of genetic
crosses
Make a tic-tac-toe board
Place the parent alleles like below:
TALL PARENT PLANT
SHORT PARENT PLANT
Let’s try another one…
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If the trait is for feather color of
parrots, then GG= Dominant and is
green.
gg= recessive and is gold.
GG allele is homozygous dominant;
(Homo- same; zygous-sex cell;
dominant- dominant)
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gg allele is homozygous recessive;
(Homo- same; zygous- sex cell;
recessive- recessive)
So from the cross above we get all
Gg. So are they Green or gold or a
mix of both?
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They are all green. Gg is called
heterozygous. Heterozygous means
different.
If a G and a g are together to make
a heterozygous trait, the trait looks
like the dominant gene or G. So,
ALL the parrots look green.
But what about the KIDS of these new,
green parrots?

Genetics of the
new, GREEN (F1)
parrots:

G
Gg x Gg
g
G GG Gg
g
Gg gg
Ratios?
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Phenotype: the “look” of the genes
Genotype: the “letters” or alleles of
the organism
PHENOTYPE
RATIOS:
3:1
GENOTYPE RATIOS:
1 GG, 2Gg
1gg
Why we needed the math: The
Dihybrid Cross
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Lets say that in peas, We cross a
Homozygous dominant Smooth,
yellow seed with a Homozygous
recessive wrinkled, green seed.
What would be the genotype and
phenotype of the F1 generation?
Setting it up
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SS= Smooth
ss= wrinkled

So we are crossing a SSYY x ssyy
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YY= yellow
yy= green
Ready, set, go!

Most important question: What are
all of the possible sperm and egg
that each plant can produce with
those alleles? (huh?)
SSYY Plant
ssyy Plant
SY
sy
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The product of this cross will all be:
SsYy, or all Smooth, Yellow peas
(F1)
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But what about the F2 generation?
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Ask the Important Question again!
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Most important question: What are
all of the possible sperm and egg
that each plant can produce with
those alleles?
SY
SsYy
Sy
sY
PEA SEED
sy
9:3:3:1
Incomplete Dominance
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What do you get when you cross a
homozygous dominant red rose with
a homozygous white rose?
Incomplete Dominance
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A Pink Rose!
Since all of the F1 are Rr= pink,
what would be the F2 generation of
all of the F1 pink roses?
1 Red: 2 Pink: 1 White
R
r
R
RR
Rr
r
Rr
rr
Codominance
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Codominance- when both alleles
contribute to the phenotype of the
organism
Multiple Alleles
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When three or
more alleles of
the same gene
exist in a
population
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i.e. blood types
(A, B, O)
Continuous Variation
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- The range of
small
differences of a
single trait in a
population.
It is usually
where several
genes effect a
single trait.