Transcript 3-15-07
3-15-10
IN
Explain the purpose of a punnett square.
Create your own monohybrid cross
3-15-10
Through
Analysis questions
OUT
Study guide
Look through your
notes preparing for
the test. Begin to
think about questions
to ask me.
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).
Predictions:
Phenotypes-- 50% droopy 50% upright
Genotypes --- 50% Dd(heterozygous)
50% dd(homozygous)
D
d
d
d
Dd
dd
Dd
dd
2. Describe the role of a Punnett square
in predicting the potential ratio of
genotypes that may result from a
particular cross.
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?
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
5. Explain why males are more likely
than females to display the phenotypes
associated with X-linked recessive traits.
6. Use your knowledge of X-linked traits
to explain the inheritance of hemophilia
in the story A royal tragedy.
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?