Lab Exercise 11: Genetics
Purpose of the lab:
The purpose of these laboratory exercises is to introduce the student to the basic concepts of
Mendelian Genetics, Punnett Squares, and Pedigrees. These concepts will reinforce the lecture
material by completing a simulation using fruit flies and working on genetics problems.
Activity 1: Mendelian Fly Genetics
Navigate to the “Mendelian Fly Genetics Simulation” available in Canvas, and choose “Breeding
Mutations in Fruit Flies” from the list. Follow the on-screen instructions to complete the
simulation, then answer the following questions.
1. What are the genotypic and phenotypic ratios of the F
2. What are the genotypic and phenotypic ratios of the F
3. Is the allele for ebony body color recessive or dominant? How do you know?
4. Why do you think the puppy litter was all dark-haired? Remember the mother was light-
haired, and the father was dark-haired.
Activity 2: Mendelian Genetics
Remember: Law of Dominance, Law of Segregation, and Law of Independent Assortment
What is Mendel’s first Law? ______________________________________________________
What is Mendel’s second Law? ____________________________________________________
What is Mendel’s third Law? ______________________________________________________
Problems: Answer these questions:
1. A brown mouse is mated with a white mouse. All of their offspring are brown. If two of these
brown offspring are mated, what fraction of their offspring will be white? (Brown is
dominant over white fur color)
2. How could you determine the genotypes of one of the brown F2 mice in the first problem?
How would you know whether the brown mouse is homozygous or heterozygous?
3. Freckles is dominant, no freckles is recessive. A man with freckles and a woman with no
freckles have three children with freckles. What are the genotypes of the parents and the
4. In one experiment, Mendel crossed a true breeding garden pea plant with green pods and a
true breeding plant with yellow pods. All the F1 plants had green pods. Which color is
5. If all offspring of a cross have the genotype Aa, the parents of the crosses would most likely
6. If tall (D) is dominant to dwarf (d), and two homozygous varieties DD and dd are crossed,
then what kind of offspring will be produced?
7. Two brown dogs mated. Their offspring were five brown puppies and two white puppies.
The most probable genotypes of the two brown dogs would be?
8. In rabbits, black hair depends on a dominant allele, B, and brown hair depends on a recessive
allele, b. Short hair is due to a dominant allele, S, and long hair to a recessive allele, s. If a
true breeding black, shorthaired male is mated with a brown, longhaired female, describe
their offspring. If two of these F1 rabbits were mated, what phenotypes would you expect
among their offspring and in what proportions?
9. If black fur color is controlled by a dominant allele (B) and brown by its recessive allele (b),
give the genotypes of the parents and offspring of a cross of a black male with a brown
female that produces 1/2 black offspring and 1/2 brown offspring.
10. In radishes, red and white are the pure-breeding colors and long and round are the pure-
breeding shapes, while the hybrids are purple and oval. The cross of a red long radish and a
white round radish will produce an F1 generation of what phenotype?
11. In cocker spaniels, black coat color (B) is dominant over red (b), and solid color (S) is
dominant over spotted (s). If a red spotted male was crossed with a black solid female and all
the offspring from several crosses were only black and solid, the genotype of the female
would be _______
12. In cocker spaniels, black coat color (B) is dominant over red (b), and solid color (S) is
dominant over spotted (s). If two black solid dogs were crossed several times and the total
offspring were 18 black solid and 5 black spotted puppies, the genotypes of the parents could
13. Tim and Jan both have freckles while their son Jay does not. Show a Punnett Square how this
is possible? If Tim and Jan have two more children, what is the probability that they have
14. Some dogs bark while trailing; others are silent. The barker gene is dominant, the silent gene
recessive. The gene for normal tail is dominant over the gene for screw tail. A barker dog
with a normal tail that is heterozygous for both characteristics is mated to another dog of the
same genotype. What fraction of their offspring will be barkers with screw tails?
Activity 2: Pedigree charts
An effective way to analyze an inheritance pattern for a specific human trait is to construct a
pedigree chart. Genetic counselors routinely use pedigree charts to understand the genetic
makeup of a couple and offer predictions on the likelihood that their offspring may inherit a
potentially lethal genetic condition. The succinct method of completing a pedigree chart permits
one to easily follow the occurrence of a specific human trait through several generations. A
circle represents females and square, males. Shading the appropriate symbol represents
phenotypes of individuals with a genetic disorder. A straight line between the two symbols
indicates a marriage between two individuals. A straight, vertical line is drawn below the above
horizontal marriage line to indicate the birth of an offspring. If more than one child is produced
then a horizontal line is written with the offspring hanging down on short vertical lines.
The pedigree chart below is for an inherited form of lung disease. What are the
genotypes for individuals a, b, c, and d?
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