Metabolic Defect Caused by Lack Of HGPRT Enzyme Genetic Problems
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1) In guinea pigs, black fur is dominant over white fur. How could an animal breeder test
whether a black guinea pig is homozygous or heterozygous?
2) A true-breeding red rose plant is crossed with a true breeding pink rose plant. Assuming
that Mendelian inheritance patterns are followed, list the genotypes and phenotypes of the
F1 generation, and the genotypes and phenotypes resulting when two F1 plants are
3) A short stem, yellow pod pea plant is crossed with a true breeding long stem, green pod pea
plant. Assuming that long stems are dominant to short stems, and green pods are dominant
to yellow pods 1) what are the genotypes and phenotypes of the F1 generation? and 2)
what are the genotypes and phenotypes resulting from a F1 x F1 cross?
4) In humans, hemophilia (bleeder’s disease) is a recessive, sex-linked trait. Use a Punnett
square to show the possible genotypes of offspring of a man who is a hemophiliac (X
and a normal, homozygous woman (XHX
), where XH
contains the normal clotting gene and
contains the gene for hemophilia.
5) Cystic fibrosis is a human disease caused by an autosomal recessive mutation. About 1 in
22 people in the human population are heterozygous carriers and have no symptoms of the
disease. A woman who has a brother with CF marries a man who has no history of CF in
a) What are the possible genotypes of the woman?
b) What is the most likely genotype of the man?
c) What is the percentage of offspring that would be affected with CF, depending upon the
genotype of the mother?
6) Lesch-Nyhan syndrome is a metabolic defect caused by the lack of the enzyme
hypoxanthine-guanine phosphoribosyl transferase (HGPRT). This disease is the result of
an X-linked, recessive mutation and results in mental retardation, self-mutilation and early
death. A normal man marries a woman who had a brother who died of LNS. Your are the
genetic counselor who will advise them on the likelihood of their having a LNS baby.
a) What are the possible genotypes for the woman?
b) What is the man’s genotype?
c) For each of the woman’s possible genotypes, what are the possible genotypes of her
offspring and the implications for survival for each of them?
7) A colorblind female, blood type A married 2 different men. One man had type AB blood and
was colorblind. The other man had type B blood and normal color vision. Three offspring
resulted from the marriages. If possible, determine the father of each of the following
a) female, Type A blood, normal color vision
b) male, Type AB blood, colorblind
c) female, Type B blood, colorblind
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8) In tomatoes, red fruit color is dominant to yellow. Suppose a tomato plant homozygous for
red is crossed with one homozygous for yellow. Determine the phenotype and genotype of
a) the F1 offspring
b) the offspring of a cross of the F1 back to the red parent
c) the offspring of the F1 back to the yellow parent
9) In humans, the allele for free earlobes is dominant to the allele for attached earlobes. A
woman with attached earlobes has children with a man who has free earlobes.
a) what is the genotype of the woman?
b) What is the genotype of the man?
c) What proportion of their offspring will have attached earlobes?
10) Fur color in tribbles is determined by a pair of alleles B and b. BB and Bb tribbles are black
and bb tribbles are white.A white female tribble is bred with a black male tribble. They have
15 white and 18 black baby tribbles. What is the genotype of the male tribble?
11) Phenylketonuria (PKU) is a human genetic disorder in which the affected individual cannot
metabolize the amino acid phenylalanine. The disease is characterized by severe mental
retardation if left untreated. The disease is caused by homozygosity for a recessive, mutant
allele. If two parents are heterozygous for the allele, what is the probability that their child
will have PKU?
12) In one experiment, Mendel crossed a purple-flowered, tall plant that had come from a
previous hybridization (i.e., it was not true breeding) with a white-flowered, dwarf plant. The
results were as follows:
a) Purple flowers, tall 47
b) White flowers, tall 40
c) Purple flowers, dwarf 38
d) White flowers, dwarf 41
e) What are the genotypes of both parent plants and all of the 4 classes of progeny?
13) Two black female mice are crossed with the same brown male. In a number of litters female
X produced 9 blacks and 7 browns and female Y produced 14 blacks. Which color is
dominant and why? What are the genotypes of the parents?
14) A farmer breeds a chicken with all white plumage with a chicken with all black plumage. All
of the F1 offspring have bluish-gray plumage. When two of the bluish-gray birds are
crossed, black, white and bluish-gray offspring are produced. Describe the mechanism of
inheritance, and the genotypes of the parents, F1’s and F2’s.
15) A couple with a newborn baby is troubled that the child does not resemble either of them.
Suspecting that a mix-up occurred at the hospital, they check the blood type of the infant
and find that it is type O. As the father is type A and the mother type B, they conclude that a
mix-up must have occurred. Are they correct?
16) In the fly Drosophila, the allele for dumpy wings (d) is recessive to the normal long-wing
allele, (D) and the allele for white eye (w) is recessive to the normal red-eye allele (W). In a
cross of DDWW with Ddww, what proportion of the offspring are expected to be “normal”
(long wings and red eyes)? What proportion are expected to have dumpy wings and white
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17) Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human
enzyme deficiency in the world, affecting an estimated 400 million people. It is also known
as “favism”, since G6PD deficient individuals are also sometimes allergic to fava beans. The
deficiency is due to an X-linked, recessive allele. A man who is allergic to fava beans
marries a woman who is not. Her father, however, was also allergic to the beans. They have
2 sons, both of whom are allergic, while neither of their two daughters are allergic to the
a) Give the proposed genotypes of the mother, father, sons and daughters
b) What is the probability that any additional sons will be G6PD deficient?
18) In Drosophila melanogaster the recessive allele p, when homozygous , determines pink
eyes. Pp or PP results in wild-type eye color. Another gene on another chromosome , has a
recessive allele s, that produces short wings when homozygous. Consider a cross between
females of genotype PPSS and males of genotype ppss. Describe the phenotypes and
genotypes of the F1 generation and of the F2 generation produced by allowing the F1
progeny to mate with one another.
19) Using information from the previous problem, what are the results of a cross of males of
genotype Ppss with females of genotype ppSs. Describe the phenotypes and genotypes of
the F1 generation.
20) In the Andadalusian fowl, a single pair of alleles controls the color of the feathers. Three
colors are blue, black and splashed white. Crosses among these three types yield the
Black x blue Blue and black (1:1)
Black x splashed white Blue
Blue x splashed white Blue and splashed white (1:1)
Black x black Black
Splashed white x splashed white Splashed white
a) What progeny would you expect from the cross blue x blue?
b) If you want to sell eggs, all of which would yield blue fowl, how should you proceed?
21) Tim and Jan both have freckles (a dominant trait). Their son Michael does not. Show with a
Punnett square how this is possible. What is the probability that they will have more children
22) Gina was surprised to find out the she suffered from red-green colorblindness. Her doctor
said to her “Your father is color-blind too, correct?” How did the doctor know this?
23) A man who has type B blood has children with a woman who has type A blood. What are
the possible phenotypes and genotypes of their children?
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24) A female with unattached earlobes and a widow’s peak hairline, and a male with attached
earlobes and a widow’s peak hairline have a child. The child has attached earlobes and a
non-widow’s peak hairline. Widow’s peak hairline is dominant to non-widow’s peak, and
unattached earlobes are dominant over attached. What are the genotypes of the parents?
What is the probability that they will have a child that has unattached earlobes and a nonwidow’s peak hairline?
25) Determine the sequence of genes along a chromosome based on the following
recombination frequencies: A—B, 8 map units; A—C, 28 map units; A—D, 25 map units;
B—C, 20 map units, B—D, 33 map units.
26) A wild type fruit fly (heterozygous for gray body color and red eyes) was mated with a black
fruit fly with purple eyes. Assume the gray body color is dominant to black, and red eyes are
dominant to purple. The offspring were as follows: 721 wild type, 751 black-purple, 49 graypurple, 45 black-red. What is the recombination frequency between these genes for body
color and eye color? Approximately how far apart are the two genes from each other?
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