Punnett Squares :
description
Transcript of Punnett Squares :
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Genetics Notes Day 2
Warm Up – What is the difference between a genotype and a
phenotype? Give an example of each.
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Bring in your PHOTOS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
We are doing “Throw Back Thursday” this week!
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A diagram that predicts the expected outcome of a genetic cross.
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Helps you keep track of traits.
Punnett Squares
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.
Dominant and recessive alleles
are represented by letters.
Punnett Squares
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A capital letter (T) is used for dominant alleles.
Punnett Squares
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A lowercase letter (t) is used for recessive alleles.
Punnett Squares
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Example (Tall or short)
T = dominant allele t = recessive allele Homozygous dominant
– Genotype = _____ Phenotype = __________
Heterozygous– Genotype = _____ Phenotype = __________
Homozygous recessive– Genotype = _____ Phenotype = __________
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If you wanted to know the type of offspring a cross between two parents would produce, you can use a punnett square.
Tt x Tt
TT,Tt for tall
Tt for short
Punnett Squares
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The letters representing the alleles from one parent are placed along the top of the square.
T t
Punnett Squares
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The letters representing the two alleles from the second
Parent are places along the side of the square.
T
t
Punnett Squares
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T t x T t
T t
T
t
Punnett Squares
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Punnett Squares
Squares are filled by writing the letter at the top beside the letter on the side.
TT Tt
Tt t t
T t
T
t
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Punnett Squares
The letters in each of the squares represents the Genotypes of the offspring that the parents could produce.
TT Tt
Tt t t
T t
T
t
TT
Tt
Tt
t t
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The genotype (genetic makeup) can be used to predict the phenotype (physical appearance) of the offspring.
Punnett Squares
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Genotype Phenotype
TT tall
Tt tall
Tt tall
t t short
Punnett Sqaures
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Punnett Squares
Probability: the ratio that a particular event could occur.
out of 4 offspring3 would be tall
1 would be short
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Punnett Squares:
•Help you keep track of traits.
•Predict genotype and phenotype.
•Calculate probability.
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Bb Bb
Bb Bb
BB x bb
b b
B
B
Genotypes: Bb, Bb, Bb, Bb
Phenotypes: All brown
Probability: 100%
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BB Bb
BB Bb
BB x Bb
B b
B
B
Genotypes: BB, BB, Bb, Bb
Phenotypes: All brown
Probability: 100% brown
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Genetics Notes Day 3
Warm Up: Create a Monohybrid cross from these parents:
Dad = heterozygous for Brown Eyes
Mom = homozygous recessive for Blue Eyes
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Bb bb
Bb bb
B b
b
b
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Dihybrid Crosses
A cross that involves two pairs of contrasting traits.
– RrYy crossed with RrYy
– RY Ry rY ry – RY Ry rY ry
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BBff x BBFF
• Bf Bf Bf Bf
• BF BF BF BF
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Ttrr x ttRr
• Tr Tr tr tr
• tR tr tR tr
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