wednesday – september 23, 2009 objectives: swbat create and analyze punnett squares. catalyst: ...
TRANSCRIPT
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Wednesday – September 23, 2009
Objectives: SWBAT create and analyze Punnett
Squares.
Catalyst: What is the difference between a
gene and an allele? How do we represent dominant
alleles? Recessive alleles?
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Agenda
Catalyst Review Making Babies Lab (GASP!) Punnett Squares Guided Practice Independent Practice Closing
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Catalyst
A gene codes for a trait- eye color, ear lobes, dimples, etc.
An allele is a different version of a gene. Ex: Brown vs. Blue eyes Ex: Attached vs. Free hanging earlobes Ex: Dimples vs. No dimples
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Review Yesterday’s Vocab
Traits Allele Homozygous Heterozygous Dominant Recessive
Check your
awesome notes!
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Remember…
GENOTYPE = combination of alleles inherited from the parents (the genes)
PHENOTYPE = physical expression of the trait
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Today, you are going to have 20 kids. What? Yes. In 15 minutes, you will have 20 kids. You will need to find someone in the
class to mate with. We will demonstrate how this works.
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Key Point #1
Punnett Squares are diagrams that are used to predict the genotypes of offspring.
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Probability…not EXACT
It is important to note that Punnett Squares only give probabilities for genotypes
It doesn’t give you the EXACT outcomes You will see when we start creating our Punnett Squares
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Key Point #2
You can never know for sure what offspring will look like, you can only predict based on probability.
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Key Point #3
We refer to the parent generation as P1 and the offspring of that generation as F1.
P1
F1
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Before we get started…
CAPTIALIZED letters are DOMINANT lowercase letters are recessiveExamples: B = brown hair (DOMINANT)b = blonde hair (recessive)Y = yellow (DOMINANT)y = green (recessive) P = purple (DOMINANT)p = white (recessive)
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Before we get started…
D = dimples
d = no dimples
D = dimples
d = no dimples
Homozygous dominant
Genotype: DD
Phenotype: have dimples
Homozygous dominant
Genotype: DD
Phenotype: have dimples
Homozygous recessive
Genotype: dd
Phenotype: no dimples
Homozygous recessive
Genotype: dd
Phenotype: no dimples
Heterozygous
Genotype: Dd
Phenotype: have dimples
Heterozygous
Genotype: Dd
Phenotype: have dimples
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Before we get started…
B = brown eyes
b = blue eyes
B = brown eyes
b = blue eyes
Homozygous dominant
Genotype: BB
Phenotype: brown eyes
Homozygous dominant
Genotype: BB
Phenotype: brown eyes
Homozygous recessive
Genotype: bb
Phenotype: blue eyes
Homozygous recessive
Genotype: bb
Phenotype: blue eyes
Heterozygous Genotype: Bb
Phenotype: brown eyes
Heterozygous Genotype: Bb
Phenotype: brown eyes
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Big Pun-nett
Let’s make our own. First things first, draw yourself box and split it into 4 squares.
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Punnett like its Hot
Now, read the problem and find the parents’ genotypes.
*Remember, use the first letter of the dominant trait.
A homozygous dominant brown eyed male mates with a blue eyed female.
BB
bb
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Punnett Squares are COOL
Parents go on the top and on the left (keep them together)
It doesn’t matter which parents goes on the top or the left B B
bb b
b
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Punnett Square Dance
Now, bring em together. The four boxes represent the possible
kids.B B
b
b
Bb Bb
Bb Bb
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Just Punnett!
Now, we analyze. Use quarters to figure out percentages.
B B
b
b
Bb Bb
Bb Bb
•How many homozygous dominant do we have? 0%
•How many heterozygous do we have? 100%
•How many homozygous recessive do we have? 0%
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Punnett baby one more time Lastly, figure out percentages by
phenotypes.
B B
b
b
Bb Bb
Bb Bb
•What percentage will have brown eyes? 100%
•What percentage will have blue eyes? 0%
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Let’s do one more on the board A heterozygous dimpled male mates
with a heterozygous dimpled female.
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Whiteboard Guided Practice: Seed Shape
Solve the following Punnett Square.
A homozygous dominant round seeded plant is crossed with a heterozygous wrinkled plant.
Find the genotype and phenotype probabilities.R = round
r = wrinkled
RrRr
RRRRR
R
r
R
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Guided Practice: Earlobes
Solve the following Punnett Square
A male with attached earlobes mates with a heterozygous free hanging earlobe female.
Find the genotype and phenotype percentages.
F = free
f = attached
ffFf
ffFff
F
f
f
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Oh, how we love Spongebob! Your teacher will now pass out the
GP & IP “Punnett Squares – Spongebob Style” worksheets
We’ll do some of them together…then you get to try the rest on your own!
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Wrap Up
Punnett Squares are diagrams that are used to predict the genotypes of offspring.
You can never know for sure what offspring will look like, you can only predict based on probability.
We refer to the parent generation as P1 and the offspring of that generation as F1.
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Exit Question
Create a Punnett Square. Do a cross of
two heterozyous parents for brown
eyes. List the genotypes & phenotypes
probabilities of both the P1 and F1 generations.
Create a Punnett Square. Do a cross of
two heterozyous parents for brown
eyes. List the genotypes & phenotypes
probabilities of both the P1 and F1 generations.