Genetics
Single Factor Inheritance
In humans, six fingers (F) is the dominant trait; five fingers is the recessive trait.
Both parents are heterozygous for six fingers.
Female Genotype:
Possible Female Gametes:
Male Genotype:
Possible Male Gametes:
Double Factor Inheritance
Humans may have Rh+ blood or Rh- blood. A person with Rh- (r) does not have a certain
protein. In humans, Rh+ dominates Rh-. Normal insulin (I) production dominates abnormal
(i) insulin production or diabetes.
Both parents are heterozygous for Rh+ and normal insulin production.
Female Genotype:
Possible Female Gametes:
Male Genotype:
Possible Male Gametes:
The father is homozygous for Rh+ and has diabetes. The mother is Rh- and homozygous for normal insulin
production. What are the possible phenotypes of their offspring? SHOW ALL WORK
In humans a type of blindness is due to a dominant allele; normal vision is the result of a
recessive allele. Migrane headaches are due to a dominant allele, and normal (no
headaches) is recessive.
A male who is heterozygous for blindness and does not suffer from headaches marries a woman who has
normal vision and does not suffer from migraines. Could they produce a child with normal vision who does
not suffer from headaches? SHOW ALL WORK
Sex Linked Inheritance
X Linkage
In humans the condition for normal blood clotting (H) dominates the condition for
nonclotting (h) (hemophilia). Both alleles are linked to the X chromosome.
A male hemophiliac marries a woman who is a carrier for hemophilia. If they HAVE A SON, what are the
chances he will be normal for blood clotting? SHOW ALL WORK
A male who has normal blood clotting marries a woman who is a carrier for hemophilia. What are the chances
that they will have a son who is normal for blood clotting? SHOW ALL WORK
In humans the condition for normal vision dominates color blindness. Both alleles are linked
to the X chromosome.
A color blind male marries a color blind female. If they have a daughter what are the chances she will have
normal vision? SHOW ALL WORK
A male with normal vision marries a woman who is color blind. She gives birth to a daughter who is also color
blind. The husband claims the child is not his. The wife insists that the child is his. Can you support the
argument of either parent? SHOW ALL WORK
Multiple Alleles
In humans the allele for blood type A and Blood Type B show incomplete dominance. A
person with both alleles has blood type AB. Both A and B dominate O.
A person with alleles for blood types A and O marries someone with alleles for blood types B and O. List the
types of blood their offspring could have and the probability for each.
A young woman with blood type O gave birth to a baby with blood type O. In a court case, she claims that a
certain young man is the father of her child. The man has type A blood.
Could he be the father?
Can it be proven on this evidence alone that he is the father?
Explain:
In humans, kinky hair (H++), curly hair (H+), wavy hair (H) and straight hair (h) are dominant
in that order. Dark hair dominates red hair.
A wavy red-haired male whose mother had straight dark hair marries a female with straight hair who has a
curly red haired father. What types of children can they produce? What are the probabilities of each? SHOW
ALL WORK
Epistatis Problems
Gene interactions
In humans normal pigmentation dominates no pigmentation (albino). An albino person will
have white hair even though he or she may also have the alleles for blonde or black hair.
An albino male who is homozygous for black hair marries a woman who is heterozygous for normal
pigmentation and has blond hair. What colors of hair can their children have? SHOW ALL WORK
Determination of Genotypes
Not all genetic problems deal with determining the phenotype of the offspring. There is a type of problem in
which the phenotypes of both parents and offspring are known and you then determine the genotype of each
individual.
Normal pigmentation (A) dominates no pigmentation (a). Dark hair coloring (D) dominates
light hair coloring (d).
Two people with normal pigmentation produce one child with dark hair, two children with light hair and two
albino children. What are the possible genotypes of the parents?
The condition for normal clotting dominates hemophilia. Both alleles are sex-linked to the X
chromosome.
Two parents produce daughters who are all carriers and sons who are normal. What are the probably
genotypes of the parents?
Deafness is due to a homozygous condition of either or both recessive alleles d and e. Both
dominant alleles D and E are needed for normal hearing.
Two deaf people marry and produce offspring who all have normal hearing. What are the probably genotypes
of the parents?