Transcript 3-15-07

3-15-10
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IN
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Explain the purpose of a punnett square.
Create your own monohybrid cross
3-15-10
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Through
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Analysis questions
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OUT
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Study guide
Look through your
notes preparing for
the test. Begin to
think about questions
to ask me.
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1. Predict the possible phenotypes and
genotypes of the offspring from a
mating of two beagles. A heterozygous
female with the dominant phenotype for
droopy ears (D) mates with a male with
recessive phenotype for upright ears (d).
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Predictions:
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Phenotypes-- 50% droopy 50% upright
Genotypes --- 50% Dd(heterozygous)
50% dd(homozygous)
D
d
d
d
Dd
dd
Dd
dd
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2. Describe the role of a Punnett square
in predicting the potential ratio of
genotypes that may result from a
particular cross.
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3. Recall that crossing-over causes
some genes on the same chromosome
to assort independently. What
relationship might you expect between
the spacing of genes on the
chromosome and their frequency of
independent assortment?
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4. Remember that the gene for eye
color in fruit flies is linked to the X
chromosome. Predict F1 and F2 results
of a initial mating between a
homozygous red-eyed female and a
white-eyed male.
F1
XR
Xr
XR
XRXr
XRXr
XRY
XRY
Y
Predictions:
Genotypes: 100% males XRY 100% females XRXr
Phenotypes: males are Red-eyed
females are red-eyed
F2
XR
XR
Y
Xr
XRXR
XRXr
XRY
XrY
Predictions:
Genotypes: If male, 50% XRY 50% XrY
If female, 50% XRXR 50% XRXr
Phenotypes: Females are red-eyed, 50%
males are red-eyed, 50% males are white-eyed
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5. Explain why males are more likely
than females to display the phenotypes
associated with X-linked recessive traits.
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6. Use your knowledge of X-linked traits
to explain the inheritance of hemophilia
in the story A royal tragedy.
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7. Consider how tall you are. How tall
will you likely be when you are fully
grown? How tall might you have been if
you were raised in a very different
situation? How do your genes and the
environment interact to determine how
tall you will be?