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.
P= Parents F1= First Filial generation (kids) F2= Second Filial generation
(grandkids)
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.
Alleles
Alleles are simply versions of genes
THE ALLELES FOR COW FUR COLOR ARE BLACK. BROWN, AND WHITE
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
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
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)
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?
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:
Gg x GgG g
G GG Gg
g Gg gg
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
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?
Setting it up
SS= Smooth YY= yellow ss= wrinkled yy= green
So we are crossing a SSYY x ssyy
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
The product of this cross will all be: SsYy, or all Smooth, Yellow peas
(F1)
But what about the F2 generation?
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
9:3:3:1
Incomplete Dominance
What do you get when you cross a homozygous dominant red rose with a homozygous white rose?
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?
1 Red: 2 Pink: 1 White
R r
R RR Rr
r Rr rrrr
Codominance
Codominance- when both alleles contribute to the phenotype of the organism
Multiple Alleles
When three or more alleles of the same gene exist in a population i.e. blood types
(A, B, O)
Continuous Variation
- The range of small differences of a single trait in a population.
It is usually where several genes effect a single trait.
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