Genetics Review
Introduction:
How do organisms come to look and act the way they do? How are characteristics passed from generation to
generation? Genetics, the study of inheritance, attempts to answer these and other questions. Through the
genetics problems presented in this packet we will investigate several simple forms of inheritance. While
completing genetics problems, you will be asked to carry out step-by-step methods which will include
reading the problem, interpreting the information given, setting up a "Key", “working the crosses”, and finally
presenting and interpreting the results of the crosses.
In order to readily converse in the language of heredity you will first need to know and understand the
follow terms. Using your Biology book (Ch. 11) and class notes, define the words below in the space
provided.
BASIC GENETICS VOCABULARY
True Breeding:
Hybrid:
Gene:
Allele:
Genotype:
Phenotype:
Homozygous:
Heterozygous:
Dominant:
Recessive:
Sex-Linked Trait:
Genetics Problems
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Genetics Problems Set #1
MONOHYBRID CROSS (Simple dominance)
Do the following on a separate sheet of paper.
1. a. In peas, green pod color is dominant to yellow pod color. Do a cross between true-breeding green and
true-breeding yellow plants. Determine the genotypic and phenotypic ratios.
b. Take two plants from the cross above and do a punnett square for that mating. Give the phenotypic
and genotypic ratios.
2. If you can roll your tongue and your wife (husband) can roll their tongue, explain how is it possible for
you to have a child that can roll their tongue and another child that cannot roll their tongue. Explain your
answer without doing a punnett square.
3. Consider blue eyes in humans to be recessive to brown eyes. Show the expected children of a
heterozygous woman with a brown eyed man whose mother had blue eyes. Include the genotypic and
phenotypic ratios.
a. Identify the genotypes of the woman, man, and the man’s mother.
What percent will homozygous dominant?
b. What percent of offspring will have blue eyes?
4. A woman has a rare eyelid abnormality called ptosis, which makes it impossible for her to open her eyes
all the way. The condition is caused by a single dominant allele. The woman's father had ptosis
(heterozygous) but her mother was normal.
a. If you have normal eyes, what will your genotype always be? If you have ptosis, what could your
genotype be? Explain your answers.
b. What are the genotypes of the woman and the woman’s parent?
c. If the woman marries a man with normal eyes, what percent of her children will have ptosis?
Genetics Problems Set #2
DIHYBRID CROSS (Simple dominance)
1. Use the following key to answer a-e.
Axial flowers are dominant to terminal flowers. Round seeds are dominant to wrinkled seeds.
a. What are the four possible phenotypes using the traits above?
b. What are all the genotypes if flowers are axial with wrinkled seeds?
c. What is the phenotype if a plant is homozygous recessive for flower position and heterozygous for
seeds shape.
d. What are all the genotypes of a terminal flower with wrinkled seeds?
e. What are all the genotypes of an axial flower with round seeds?
Genetics Problems
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2. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled
by genes on different chromosomes. Assume further that normal coat color (N) is dominant to black (n)
and brown eyes (B) are dominant to blue (b). A female with normal coat color and brown eyes (assume
her father was homozygous recessive for both traits) mates with a male with black coat color and blue
eyes.
a. What is the genotype of the female?
b. What is the genotype of the male?
c. How many offspring will be normal coat with brown eyes? How many will have black coat? Show by
making a punnett square.
Genetics Problems Set #3
SEX-LINKED TRAITS
1. HEMOPHILIA
Most people’s blood clots normally. Hemophilia is a blood disorder which causes blood not to clot
properly. The allele for hemophilia is recessive to the allele for normal blood clotting. These alleles are
located on the human X chromosome. The Y chromosome is a genetic "blank" for this trait; it contains no
allele for the blood-clotting gene.
A number of cases of hemophilia have occurred among male descendants in the family of England's
Queen Victoria. She, however, did not have hemophilia.
a. What is the genotype of a male with hemophilia? A female with hemophilia?
b. What are all the genotypes of a female if she does not have hemophilia?
c. If a man who has hemophilia has children with a woman who is normal (homozygous dominant),
what is the probability they will have boys with the disease? What percent of girls will be
carriers of the disease? Show with a punnett square.
d. Explain what it means to be a “carrier” of a sex-linked trait? Who is always the carrier?
2. RED-GREEN COLOR BLINDNESS
Red/green color-blindness in humans is X-linked.
a. A woman has normal vision, but her father is color-blind. Is she necessarily a carrier? Explain.
b. What is the probability of having a child who is color-blind if the mother is heterozygous for the
trait and the man is colorblind? Show with a punnett square.
c. A boy is color blind, but both his parents are able to see color. What are all of their genotypes?
d. Diagram all genotypes and phenotypes of parents and expected children in a family where the
woman is a carrier for the color blindness trait, and the man is normal. Show with a punnett
square.
Genetics Problems
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e. Why do boys (most of the time) get sex-linked traits? Explain in terms of X and Y chromosome.
Genetics Problems Set #4
BEYOND SIMPLE DOMINANCE
1. A red carnation is crossed with a white carnation and the resulting offspring are all pink
(indicating incomplete dominance).
a. What are the probabilities (in %) of red, white, and pink offspring resulting of a cross between
a pink and a white carnation?
b. Could Red offspring be made from a cross of a White carnation with a Pink one? ____________
2. A curly haired person and a straight haired person mate and all their offspring have wavy hair
(note that wavy hair is a phenotype in between that of the curly and straight haired individuals).
What would be the result of a cross between two wavy haired individuals? (give phenotype %’s)?
3. A roan bull (male) is mated with a white cow (female).
a. What are the probabilities that the offspring will be white, brown, and roan?
b. Could Red offspring be born to a White cow mated with a Roan bull?
4. A man with type AB blood is married to a woman with type O blood. What are all the possible
blood types of their children?
Genetics Problems
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