Pedigree Problems
Tongue rolling
The ability to roll your tongue is caused by a dominant gene (R). If you can't roll your tongue, you are
a non-roller and must be homozygous recessive (rr).
A father cannot roll his tongue but a mother can. Of their four children, one daughter cannot roll her
tongue. The other daughter and both sons can roll their tongues.
1. Complete the pedigree chart including genotype.
Dominant Male
Dominant Female
Recessive Male
Recessive Female
2. What percent of the offspring are homozygous non-rollers?
3. What percent of the offspring are heterozygous rollers?
4. Can the parents produce a homozygous dominant child?
Eye color
The color of your eyes is caused by pigment molecules in the iris, the ring that surrounds the black
pupil in the center. While eye color is actually more complicated than the this, dark eyes (such as
brown or black) is dominant (E) and light eyes (such as blue or grey) is recessive (e).
A father and a mother both have brown eyes. Their two sons have blue eyes and their two daughters
have brown eyes. One daughter carries the gene for blue eyes, the other doesn't.
1. Complete the pedigree chart including genotype.
Dominant Male
Dominant Female
Recessive Male
Recessive Female
2. What percent of the children are homozygous recessive?
3. If one son gets married and all his children have brown eyes, what must the genotype of the his
wife be?
Diabetes
Diabetes is a disorder of the pancreas in which insulin cannot be produced or is not effective. As a
result, blood sugar cannot be properly controlled.
Diabetics have a homozygous recessive genotype (dd).
A father carries the recessive gene for diabetes and a mother does not (generation 1). They have two
children (generation 2), a daughter and a son. The daughter does not suffer from diabetes and marries a
man who does not carry the gene for diabetes. They have one child, a girl who is a carrier (generation
3). The son marries a diabetic woman and they have two boys, both who suffer from diabetes
(generation 3).
1. Complete the pedigree charts including genotype.
Dominant Male
Dominant Female
Recessive Male
Recessive Female
2. Can parents in generation 1 produce a child with diabetes?
3. How many individuals in the entire generation 2 suffer from diabetes (1,2,3, or 4)?
4. If you knew that the girl in generation 3 didn’t suffer from diabetes, what is the best way to
write her genotype?
5. What genotype must the boys in generation 3 marry so their children do not suffer from
diabetes?
LUNG DISEASE
Below is a pedigree for an inherited lung disease. Provide the genotypes of each of the individuals
marked with lower case letters.
HEART DISEASE
Below is a pedigree for an inherited heart disease. What is the probability that their child F would
have the inherited heart disease?
BLOOD TYPE
Red blood cells have many types of molecules sticking out of their cell membranes. Some of these are
glycoproteins that determine your blood type.
The genes that code for these glycoproteins exhibit something called "co-dominance" where IA and IB
are both equally dominant but O is still recessive.
The genotype for blood type A is written as IAIA or IAi (where "i" is recessive). Blood type B is IBIB or
IBi and blood type O is ii.
But put IA and IB together and you get another blood type, AB, the co-dominant type, where neither the
A or B is recessive to the other.
A father has blood type A and a mother has blood type AB. They have 3 children, a son with blood
type A, another son with blood type AB, and a daughter with blood type B. The daughter then marries
a man with blood type O and they have a daughter with type O.
1. Complete the pedigree charts including genotypes.
Male
Female
2. What blood type can the parents in generation 1 NOT produce?
3. What other blood type can be produced in generation 3?
4. Could the husband of the daughter in generation 2 have blood type B and still produce a type O
child?
Questions
1. A homozygous dominant female is represented by a(n):
2. In this tongue rolling cross, Rr x rr, what percent of the offspring will be homozygous
recessive?
3. The genotype for a tongue-roller is:
4. The genotype for blue eyes is:
5. In this eye color cross, Dd x DD, what percent of the offspring will have blue eyes?
6. True or False? A pedigree is a quick way to see all the genotypes and phenotypes in an entire
family.
7. True or False? A male with diabetes would be represented by a half filled circle.
8. True or False? A man and woman both with type B blood can produce a child with blood
type O.
9. What is the genotype for the co-dominant blood type?