Make a Baby Lab
Determining Phenotypes and Possible Genotypes
Humans have 23 pairs of chromosomes. One of those pairs is the sex chromosomes, either XX or XY; the
other 22 pairs are autosomes. These chromosomes are homologous. One chromosome came from the
maternal side and one from the paternal side. Some traits on these chromosomes are dominant and some
are recessive. If an individual receives one or two copies of the dominant trait, that trait will be expressed
in their phenotype and the recessive trait will not. If the individual receives two copies of the recessive
trait, the individual will express the recessive trait and not the dominant trait. Genotypes are called
homozygous or heterozygous depending on whether they possess two of the same allele or one of each.
PURPOSE
In this activity, you will determine your phenotypes and possible genotypes for common characteristics.
The class will then be polled to determine if the dominant characteristic is the most frequently occurring.
PROCEDURE
1. Determine your individual phenotype based on the characteristics listed in the reference table provided.
Fill out the “your phenotype” column of the data and observations section.
2. After determining your phenotype for all of the traits mentioned, we will poll the class to determine the
ratio of dominant to recessive individuals in our classroom for each trait. Explore whether the dominant
characteristic is actually the most frequent.
3. Predict your genotype for each trait using the symbols provided on the data table. If you are dominant
for a trait, then you may be either heterozygous or homozygous. If you have one parent of each
phenotype, you are heterozygous. If you have two parents that both express the dominant phenotype, you
could still be heterozygous—there is no way to tell without a larger pedigree study. If you are recessive
for the trait, your only genotype choice is homozygous.
If you have a dominant phenotype, we will determine your genotype by simply flipping a coin to
determine your second allele. If the coin lands on heads, then you will use a dominant allele
(making you homozygous dominant) and if it lands on tails, then you will use a recessive allele
(making you heterozygous).
4. You should now have your phenotype and genotype for every trait completed in the chart given. You
are going to cross your genotype for each trait to the person beside you to create your imaginary progeny
(offspring).Write your mate’s genotypes in the “imaginary mate’s genotype”.
5. Using your genotype and your mate’s genotype, predict the most likely phenotype of your possible
progeny.
Note: Choose the MOST LIKELY phenotype of your child. If there is a 50:50 chance between 2
traits, then once again flip a coin (heads will be dominant, tails will be recessive).
6. Now that you know what your child will look like, discover whether your baby is going to be a boy or
girl. The father of the baby needs to flip a coin to determine if they are going to give their X or Y
chromosome. Remember, the female automatically gives her X chromosome so the father solely
determines the sex of the baby. Heads = X chromosome, Tails = Y chromosome.
7. Finally, name your precious bundle of joy.
8. Answer the analysis questions on your student answer page
CONCLUSION QUESTIONS
1. Were the dominant characteristics always the most frequent in the class? Explain how a dominant trait
could be less common than a recessive trait.
2. What is the difference in autosomal and sex-linked chromosomes?
3. Sometimes traits may be sex-linked. This means that the allele for that trait is
located on the X chromosome, and there is not an allele on the Y chromosome for that trait.
This means females (XX) will have two alleles for that trait but males (XY) will only have one. Two
examples of sex-linked traits that are recessive are hemophilia and colorblindness, and an
example of a dominant sex-linked trait is incontinentia pigmenti (which causes a type of skin lesions,
rashes, and other symptoms). Use this information to answer the following questions:
a. A male who has hemophilia and a female who does not have hemophilia decide to have
children, but they want to know if there is a chance that their kids could have hemophilia. There
has never been a single person with hemophilia in the female’s family history. Could they have a
child with hemophilia? Use a Punnett square to support your answer.
b. A couple adopts a female child that has colorblindness. What would the genotype of her
parents have been? Use a Punnett square to support your answer.
c. Sally and Harry want to have children; however, Harry’s father has incontinentia
pigmenti. Harry and Sally are afraid that their children might have this disorder, and that
Harry might be a carrier. What would you advise them? Use a Punnett square to support
your answer.
4. The majority of you do not know your blood type so I didn’t include that during your “mating”.
Assume you had homozygous A blood while your partner had heterozygous B blood. Tell the possible
phenotypes of your offspring. Show the Punnett square illustrating your work.
5. Look at your crosses for freckles and dimples. What are the chances that your offspring will have both
freckles and dimples? Show the work below. This is a dihybrid problem so you must show both Punnett
square.
Additional Questions
1. Some traits, such as hair and eye color, are polygenic; therefore, it is not as simple as merely looking at
your phenotype to figure out your exact genotype. Define the term polygenic and explain why this would
result in the range of phenotypes that are seen for traits such as hair and eye color.
2. All of the traits studied today exhibited complete dominance.
a. Explain complete dominance is different than incomplete and codominant inheritance.
b. Explain how the phenotype of a heterozygote would be different if it were a trait showing
incomplete dominance than if it were a trait showing complete dominance.