Today’s Agenda…
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Bellringer: What does it mean to be
homozygous for a trait? What about
heterozygous?
Turn in writing from yesterday
Genetics Part 2
Genetics
Part 2
Today’s Goals…
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I can identify Mendel’s role in genetics
I can use Punnett squares to predict the
results of crosses
I can compare and contrast an individual’s
phenotype and genotype
Punnett Squares
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A punnett square is a chart that shows all
the possible combinations of alleles that
can result from a genetic cross
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Helps determine the probability of a particular
outcome
Punnett Squares
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Page 311
The possible alleles that the parents can pass
on are written across the top and left side
The boxes represent possible combinations of
alleles that offspring can inherit
Each box has an one allele from each parent,
for a total of 2
Punnett Square
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The allele that each parent will pass on is
based on a chance
You can also use a Punnett square to
predict probabilities!
Look at Applying Math on page 311
Phenotypes and Genotypes
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Phenotype: an organism’s physical
appearance
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Ex. Tall or short
Genotype: an organism’s allele
combination
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Ex. TT, tt, Tt
Phenotypes and Genotypes
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If you were to look at tall plants you would
not be able to see the difference because
they have the same phenotype, but they
have two different genotypes
Short pea plants would all have the same
phenotype and genotype
Mendel and the Pea Plants
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Mendel’s experiments with pea plants lead
to modern genetics
He crossed two homozygous (purebred)
pea plants (one tall/one short)
He created heterozygous (hybrid) plants
that were a combination of their parents
(all tall)
Mendel and Probability
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When Mendel crossed two hybrid pea
plants, ¾ of the offspring were tall and ¼
was short
The probability of producing a short pea
plant was 1 in 4 or 25%
Mendel was the first scientist to recognize
that probability can be used to predict the
results of genetic crosses
Revisiting Today’s Goals…
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I can identify Mendel’s role in genetics
I can use Punnett squares to predict the
results of crosses
I can compare and contrast an individual’s
phenotype and genotype