Transcript 11-2 - Cloudfront.net

Chapter 11-2:
Fundamentals of Genetics
Homozygous vs. heterozygous
• Homozygous = alleles for a
certain trait are the same.
–aa, AA
• Heterozygous = alleles for a
certain trait are different.
–Aa
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Genotype vs. Phenotype
• Genotype = genetic makeup of an
organism.
–aa, AA, Aa
• Phenotype = Physical expression
of genotype.
–Tall, short
“How do you Pheel Physically?”
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Probability in genetics
• Mendel grew thousands of
plants and arrived at his laws
after counting many offspring.
• Laws of chance explain his
findings.
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The larger the number
of trials (flips), the
closer the ratio comes
to the expected ratio.
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This is an example of the basic
law of probability.
When several possible events can
happen
and
There is no bias
then
There is an equal chance of them
all happening.
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What does this
have to do with
genetics?
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The law of probability
allows us to predict what
offspring will result from a
genetic cross.
x
=
?
Probabilities Predict Averages
Probabilities predict the
average outcome of a large
number of events (not
necessarily the exact
outcome).
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The Punnett SquareMy name is
Punnett
Spongebob
Punnett
Pants
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Punnett Square
• Helpful way to predict the
results of a cross.
• The PS shows all possible
outcomes of a genetic cross.
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Setting up a
Punnett
Square is
like
determining
possible
outcomes
from flipping
2 coins.
2 Coins:
H
h
H
h
HH
Hh
Hh
hh
•A capital letter
represents the
dominant allele for
tall.
•A lowercase letter
represents the
recessive allele for
short.
•In this example,
•T = tall
•t = short
Punnett Squares
Parent 2
Punnett Square
T
TT
T
gametes
t
Tt
Tt
t
Tt
Tt
Parent 1
tt
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Monohybrid (single gene)
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–
Probability can be used to predict
• average outcome of many events.
• precise outcome of any event.
• how many offspring a cross will
produce.
• which organisms will mate with
each other.
–Compared to 4 flips of a coin, 400 flips
of the coin is
• more likely to produce about 50%
heads and 50% tails.
• less likely to produce about 50%
heads and 50% tails.
• guaranteed to produce exactly 50%
heads and 50% tails.
• equally likely to produce about 50%
heads and 50% tails.
–Organisms that have two different
alleles for a particular trait are said to
be
• hybrid.
• heterozygous.
• homozygous.
• recessive.
Two F1 plants that are homozygous for
shortness are crossed. What
percentage of the offspring will be
tall?
• 100%
• 50%
• 0%
• 25%
The Punnett square allows you to predict
• only the phenotypes of the offspring
from a cross.
• only the genotypes of the offspring
from a cross.
• both the genotypes and the
phenotypes from a cross.
• neither the genotypes nor the
phenotypes from a cross.