mendel and his discoveries
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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. Crosses between parents that differ in only one trait are called MONOHYBRID CROSSES. - PowerPoint PPT PresentationTRANSCRIPT
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Mendel and His Discoveries
Chapter 11
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Gregor Mendel
Gregor Mendel (1822-1884) Experimented with pea plants and developed fundamental rules of genetics and patterns of inheritance.
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Punnett Squares
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)
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Mendel and Pea Plants
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.
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Alleles
Alleles are simply versions of genes
THE ALLELES FOR COW FUR COLOR ARE BLACK. BROWN, AND WHITE
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Prediction of Genetic Crosses
The alleles for tallness of a plant: TT= Dominant (Tall) tt= Recessive (Short)
How do we know for sure that they would all be tall?
The Punnet Square
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Punnett Squares
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
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Let’s try another one…
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.
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But what about the KIDS of these new, green parrots?
Genetics of the new, GREEN (F1) parrots:
Gg x GgG g
G GG Gg
g Gg gg
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Ratios?
Phenotype: the “look” of the genes Genotype: the “letters” or alleles of
the organism
GENOTYPE RATIOS:
1 GG, 2Gg 1gg
PHENOTYPE
RATIOS:
3:1
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Why we needed the math: The Dihybrid Cross
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?
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Setting it up
SS= Smooth YY= yellow ss= wrinkled yy= green
So we are crossing a SSYY x ssyy
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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)
But what about the F2 generation?
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Ask the Important Question again!
Most important question: What are all of the possible sperm and egg that each plant can produce with those alleles?
SsYy
PEA SEED
SY
Sy
sY
sy
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9:3:3:1
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Incomplete Dominance
What do you get when you cross a homozygous dominant red rose with a homozygous white rose?
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Incomplete Dominance
A Pink Rose!
Since all of the F1 are Rr= pink, what would be the F2 generation of all of the F1 pink roses?
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1 Red: 2 Pink: 1 White
R r
R RR Rr
r Rr rrrr
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Codominance
Codominance- when both alleles contribute to the phenotype of the organism
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Multiple Alleles
When three or more alleles of the same gene exist in a population i.e. blood types
(A, B, O)
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Continuous Variation
- The range of small differences of a single trait in a population.
It is usually where several genes effect a single trait.