Download Applied Genetics - Net Start Class

Name ___________________
Date ____________________
Applied Genetics
Punnett Squares
A. The disease cystic fibrosis is caused by the recessive allele n.
1. What percentage of the children of a couple with genotypes NN and Nn will probably have cystic
fibrosis? __________________
Parent genotypes: ________ X ________
F1 genotypic ratio: __________________
F1 phenotypic ratio: _________________
2. If both parents are heterozygous for cystic fibrosis, what percentage of the children will probably
have the disease? ________________
Parent genotypes: ________ X ________
F1 genotypic ratio: __________________
F1 phenotypic ratio: _________________
B. Phenylketonuria (PKU) is an autosomal recessive genetic disease in which the body cannot safely break down
the amino acid phenylalanine. If a modified diet is not strictly observed, PKU will cause severe brain
damage. To avoid this problem, people with PKU must eat a diet low in phenylalanine. A normal couple has a
child with PKU.
1. What is the probability that this couple’s next child will have PKU?
___________________
2. What is the probability that this couple’s next child will be
homozygous for the normal allele? ____________
3. What does Nutrasweet© contain? ______________________
5. What does this have to do with PKU? ____________________
________________________________________________
C. Achondroplasia, one form of dwarfism, is caused by the dominant allele A. Embryos with the genotype AA
do not survive. Suppose a couple with achondroplasia get married and have children.
1. What phenotypic ratio would you observe in the couple’s children?
_______________________
2. One of this couple’s children, who has a normal phenotype,
marries a person who is also a normal phenotype.
What percentage of the children from this marriage is
likely to have achondroplasia? _____________________
3. In most cases of achondroplasia, two normal parents have a child with achondroplasia. How can this
happen? ____________________________________________________________________
Human Pedigrees
A. Use the following symbols to work out the next problem:
Normal male
XBY
Normal female
b
Color-blind male X Y
Color-blind female
I
1
XBXB or XBXb
XbXb
2
II
3
4
5
6
7
III
8
9
10
11
12
13
IV
14
1.
2.
3.
4.
5.
6.
15
16
17
18
19
What does a square mean in a pedigree? Male Female Undetermined
What does a circle mean?
Male
Female Undetermined
When should a square or circle be colored in? ___________________________________________
What is the genotype of a color-blind male? ______________
What is the genotype of a color-blind female? ____________
Write all genotypes for all individuals in the pedigree chart and indicate carriers by half-filled
circles/squares.
B. Huntington Disease, a disease of the nervous system, is caused by an autosomal dominant gene. The
pedigree chart below illustrates a family with individuals who have Huntington disease. Homozygous
dominant is lethal to the fetus. Use the chart to answer the questions that follow.
I
1
2
II
3
4
5
6
7
8
9
III
10
11
12
13
14
15
What is the probable genotype of person 4 in generation II? ________
Explain. ____________________________________________________________________
What are the probable genotypes of individuals 8 and 9 in generation II? ________________
Explain. ____________________________________________________________________
What is the probability that person 14 in generation III will NOT have Huntington disease?
__________________________________________________________________________
6. Use the color yellow to shade in the shapes of those individuals who can be determined to carry the
Huntington gene.
7. Identify the individuals whose genotypes cannot be determined without more information by putting
a question mark in their square or circle and coloring the shape blue.
1.
2.
3.
4.
5.
C. Duchenne Muscular Dystrophy is a deadly disorder in which the muscles grow progressively weaker. The
disease is caused by a recessive gene on the X chromosome. The pedigree chart below illustrates the
inheritance pattern of this gene. Use the chart to answer the questions that follow.
Normal male
XDY
Normal female
XDXD or XDXd
d
Duchenne male X Y
Duchenne female
XdXd
I
1
2
II
3
4
5
6
III
1.
2.
3.
4.
5.
7
8
9
10
11
Is Duchenne Muscular Dystrophy more likely to occur in males or females? Males Females
Explain. __________________________________________________________________
Individual 8 in generation III is a female with this disorder. How did she inherit this
disease? __________________________________________________________________
Individual 11 in generation III has this disorder, yet his father did not. How is this genetically
possible? __________________________________________________________________
Individual 7 from generation III does not have the disease, yet his mother was a carrier and his
father had the disease. How is this possible? __________________________________
__________________________________________________________________________
D. Autosomal Recessive Polycystic Kidney Disease (ARPKD) is a genetic disorder in which multiple fluid-filled
cysts develop on the kidneys resulting in enlarged and damaged kidneys. In the blanks provided, write as
much of the genotype as can be determined from the information provided. Assume the shaded symbols
represent the homozygous recessive genotype, pp. Be sure to correctly identify carriers. The trait is NOT
sex-linked.
I
II
III