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Vanie Mangal, Robert Rock, Keturah Reed, Christopher Reyes
A.P. Biology
December 28, 2007
Period C-3
11. Imagine that a newly discovered, recessively inherited disease is expressed only in
individuals with type O blood, although the disease and blood group are independently
inherited. A normal man with type A blood and a normal woman with type B blood have
already had one child with the disease. The woman is now pregnant for a second time.
What is the probability that the second child will also have the disease? Assume that both
parents are heterozygous for the gene that causes the disease.
Blood Type
A= A antigens on blood cells
O= no antigens on blood cells
B= B antigens on blood cells
Mother
BODd
x
x
Disease
D= Dominant allele which doesn’t
trigger the disease.
d= Recessive allele which triggers
the disease.
Father
AODd
AD
Ad
OD
Od
BD
ABDD
ABDd
BODD
BODd
Bd
ABDd
ABdd
BODd
BOdd
OD
AODD
AODd
OODD
OODd
Od
AODd
AOdd
OODd
OOdd
There is a 1 in 16 chance of giving birth to a child with the disease.
12. In tigers, a recessive allele causes an absence of fur pigmentation (a white tiger) and
cross-eyed condition. If two phenotypically normal tigers that are heterozygous at this
locus are mated, what percentage of their offspring will be cross eyed? What percentage
will be white?
Alleles
O= normal tiger with fur pigmentation and regular eyes
o= white tiger with crossed eyes
O
o
O
OO
Oo
o
Oo
oo
25% of the offspring will be white and cross-eyed while the other 75% will appear
normal.
13. In corn plants, a dominant allele “I” inhibits kernel color, while the recessive allele
“i” permits color when homozygous. At a different locus, the dominant allele “P” causes
purple kernel color, while the homozygous recessive genotype “pp” causes red kernels. If
plants heterozygous at both loci are crossed what will be the phenotypic ratio of
offspring?
Alleles
I= inhibits kernel color
i= permits kernel color when homozygous
P= purple kernel color
p= red kernel color when homozygous
IP
Ip
iP
ip
IP
IIPP
IIPp
IiPP
IiPp
Ip
IIPp
IIpp
IiPp
Iipp
iP
IiPP
IiPp
iiPP
iiPp
ip
IiPp
Iipp
iiPp
iipp
No Kernel Color: Purple Kernel Color: Red Kernel Color
12
:
3
:
1