Part 1: Simulating a monohybrid cross: (Hh X Hh)
Procedure:
- Record the results of two sequential coin tosses. Heads will represent
the dominant allele (H) and tails will represent the recessive allele (h). The only
possibilities that can be made from this selection are: HH (homozygous hair), Hh
(heterozygous hair), or hh (homozygous hairless). Mark the resulting genotype and
phenotype in the data table in results. Each of the two coin-toss results represents a
possible outcome from the contribution of each parent. - The paired coin toss will be performed 15 times (a total of 15 trials).
- Complete the data table in Part 1. Describe the genotype and phenotype for each
individual outcome.
Part 1: Simulating a monohybrid cross
Data Table
Trial Offspring Genotype Offspring Phenotype - What is the dominant trait? How do you know it is dominant?
Answer: - What is the recessive trait?
Answer: - What are the genotypes of the parents?
Answer: - What are the phenotypes of the parents?
Answer: - Fill in the Punnet Square below using the parents given in the procedure:
Male Female - What is the genotypic ratio?
Answer: - What is the phenotypic ratio?
Answer:
Part 2: Dihybrid Crosses- Crosses that involve 2 traits - Determine the parental genotypes from the example below, the word "heterozygous" is
the most important clue, and you would also need to understand that self-fertilized means
you just cross it with itself. When choosing letters to represent your genes, you’ll need to
choose one letter per characteristic. If it is dominant it will be capitalized and if it is
recessive it will be lower case.
o RrYy x RrYy - Determine the gametes. This might feel a little like the FOIL (first, outer, inner, last)
method you learned in math class. Combine the R's and Ys of each parent to represent
sperm and egg. Do this for both parents:
Figure 3: Gametes after "FOIL": RY, Ry, ry (parent 1) and RY, Ry, rY, ry (Parent 2) - Set up a large 4x4 Punnett square in the results section, crossing RRYy x Rryy. Place
one gamete set from the parent on the top, and the other on the side. Refer to the figure
below as an example of how to set up the Punnett Square (the example below is a different
cross than what you will complete in the results section.
Part 2:
Set up 4 x 4 Punnett Square crossing RrYy x RrYy below:
Part 3: Sex-linked or X-linked inheritance
Complete the questions below. - In fruit flies, eye color is a sex linked trait. Red is dominant to white. What are the sexes and
eye colors of flies with the following genotypes?
a. XRXr
Answer:
b. XRY
Answer:
c. XrXr
Answer:
d. XRXR
Answer:
e. XrY
Answer: - What are the genotypes of these flies:
a. White eyed, male
Answer:
b. Red eyed female (heterozygous)
Answer:
c. White eyed, female
Answer:
d. Red eyed, male
Answer: - Show the cross of a white eye female XrXr
with a red-eyed male XRY
.
Answer: - Show a cross between a pure red eyed female and a white eyed male. What are the genotypes
of the parents?
Answer:
How many offspring are:
a. white eyed, male
Answer:
b. white eyed, female
Answer:
c. red eyed, male
Answer:
d. red eyed female
Answer: - Show the cross of a red eyed female (heterozygous) and a red eyed male. What are the
genotypes of the parents?
Answer:
How many offspring are:
a. white eyed, male
Answer:
b. white eyed, female
Answer:
c. red eyed, male
Answer:
d. red eyed, female
Answer: - In humans, hemophilia is a sex linked trait. Females can be normal, carriers or have the
disease. Males will either have the disease or not (but they won't ever be carriers)
XHXH = female, non-hemophilic
XHXh = female, carrier
XhXh = female, hemophiliac
XHY = male, non-hemophilic
XhY = male,hemophiliac
Show the cross of a man who has hemophilia with a woman who is a carrier. What is the
probability that their children will have the disease?
Answer:
Part 4: Incomplete Dominance and Codominance
Incomplete dominance was first recorded in plants. The German scientist Josef Kolreuter bred
red and white carnations, expecting to get offspring with the dominant red coloration. Instead,
many came up pink! Kolreuter found that neither allele was fully dominant in his flowers and
identified the concept of incomplete dominance.
An example of codominance is seen in MN blood group system of humans. MN blood type is
governed by two alleles, M and N. Individuals who are homozygous for the M allele have a
surface molecule (called the M antigen) on their erythrocytes. Similarly, those homozygous for
the N allele have the N antigen on their erythrocytes. Heterozygotes—those with both alleles—
carry both antigens. An example of codominance for a gene with multiple alleles is seen in the
human ABO blood group system. Persons with type AB blood have one allele for A and one for
B; the O allele is recessive (its expression is masked by the other alleles).
Complete the questions below. - By observing flower color in carnations, is it possible to unambiguously determine the
genotype? YES/NO
a. Is the same true for flower color in snow peas in Part 2? YES/NO. Why or why not?
Answer: - If two individuals with blood type AB have children, what are the odds that each of their
offspring will have the AB blood type?
Answer:
POST LAB ASSIGNMENT - In cats, the gene for calico (multicolored) cats is both sex-linked and codominant. Due to a
phenomenon known as dosage compensation, females that receive a B and an R gene have
black and orange splotches on white coats. Males can only be black or orange, but never calico.
a. What would a calico cat's genotype be?
Answer:
b. Show the cross of a female calico cat with a black male?
Answer:
c. What percentage of the kittens will be black and male?
Answer:
d. What percentage of the kittens will be calico and male?
Answer:
e. What percentage of the kittens will be calico and female?
Answer: - Show the cross of a female black cat with a male orange cat?
Answer:
a. What percentage of the kittens will be calico and female?
Answer:
b. What color will all the male cats be?
Answer: - A disputed paternity case! Hermione's new baby has a blood type of O. Her blood type is B
and Ron Weasley's is A. Harry Potter (blood type AB) insists he is the child's father. CAN THIS
BE TRUE???!
Answer: - A woman who is a carrier marries a non-hemophilic man. Show the cross. What is the
probability that their children will have hemophilia? What sex will a child in the family with
hemophilia be?
Answer: - A woman who has hemophilia marries a non-hemophilic man. How many of their children
will have hemophilia, and what is their sex?
Answer:
Sample Solution