SAN DIEGO MESA COLLEGE
School of Natural Sciences & Mathematics
Intro Molecular & Cellular Biology Lab (BIO 210A); Instructor: Elmar Schmid, Ph.D.
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Geenneettiicc TTrraaiittss
____________________
(Student Name)
Assignments
1. Determine your own phenotype for each of the heritable traits listed and
explained in Table 1 (see Website) and protocol them in the Assignment Table
1 below.
2. Based on your noted phenotype, record your genotype for each of the traits
examined in this lab
- Remember: if you found out that you have a recessive characteristic for a
certain trait, you must have both recessive alleles on both of your homologous
chromosomes; you are homozygous recessive for this trait!
- But if you have a dominant characteristic you may either have two dominant
alleles for this trait, or one dominant and one recessive allele; under these
circumstances you may be homozygous dominant or heterozygous
3. Compile the class data for each of the traits in the right column of the
Assignment Table and calculate the class room percentages for each of the
traits with the help of your instructor
4. Analyze your findings and answer the following questions below:
a. For the traits observed, did you find that the dominant allele was expressed
most often in your class?
____________________________________________________________
b. Did you observe the typical Mendelian 3:1 pattern (75% dominant; 25%
recessive) for the examined dominant and recessive phenotypes in the
classroom?
_____________________________________________________________
If no, which factors do or might account for the discrepancy?
_____________________________________________________________
_____________________________________________________________
c. For which of the traits you examined did you NOT find the dominant
phenotype be the most prevalent in the class room population?
_____________________________________________________________
_____________________________________________________________
d. How would you explain the eventual occurred discrepancies?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
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SAN DIEGO MESA COLLEGE
School of Natural Sciences & Mathematics
Intro Molecular & Cellular Biology Lab (BIO 210A); Instructor: Elmar Schmid, Ph.D.
5. After completion of the table below, pick a member of your lab to serve as a
“model individual”
6. Everyone in the lab should stand up at this point
7. Have the “model individual” call out his or her phenotype for each of the
traits studied and previously recorded in the Assignment Table 1 above. As
each phenotype is called out, all those who do not have this phenotype
should sit down
8. Proceed with this until no one else is left standing. Analyze your findings and
then answer the following questions below.
a. How many characteristics/traits had to be called out until the “model
individual” turned out to be truly individual regarding the examined traits?
______ characteristics
Note: keep in mind that humans have about 40,000 traits; here we are only looking
at 11 of these 40,000 !!
b. In the United States, as an open and immigration nation, a great deal of
mixing of genotypes has taken place through its history. In a country where
there is little influx of other groups, would you expect a similar “model
individual” to stand out sooner or later than observed in you lab today?
Sooner ____
Later _____
Why? ________________________________________________________
_____________________________________________________________
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SAN DIEGO MESA COLLEGE
School of Natural Sciences & Mathematics
Intro Molecular & Cellular Biology Lab (BIO 210A); Instructor: Elmar Schmid, Ph.D.
Assignment Table: Classroom Data – Human genetic traits
Personal Data
Human trait
Your
phenotype
Your
possible
genotype(s)
Classroom Data
Number
Percentage Ratio
(% : %)
Dominant Recessive
Dominant Recessive
Dimples
(D or d alleles)
Free ear lobe
(E or e alleles)
Widow’s peak
(skip if baldness
exists)
(W or w alleles)
Ability to taste
PTC
(T or t alleles)
Interlocking
fingers
(F or f alleles)
Bent little finger
(B or b alleles)
Long palmar
muscle
(L or l alleles)
Pigmented iris
(P or p alleles)
Mid digital hair
(M or m allele)
Six fingers
(S or s allele)
Second finger
length
(a sex/genderinfluenced trait)
(M= male; f =
female)
(MS or FS allele)
Calculations:
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SAN DIEGO MESA COLLEGE
School of Natural Sciences & Mathematics
Intro Molecular & Cellular Biology Lab (BIO 210A); Instructor: Elmar Schmid, Ph.D.
9. Instead of considering the inheritance of only ONE of the traits just studied,
now consider the inheritance of two of these traits. All of these 11 traits
happen to be unlinked, i.e. they are not located on the same but each of them
on a different chromosome, thus Mendel’s Principle of Independent
Assortment applies
a. What is the phenotype of a person with the genotype EETT?
________________________________________________
b. What gamete genotypes could this individual produce?
___________________________________________
c. What is the phenotype of a person with the genotype eett?
___________________________________________
d. What gamete genotypes could this individual produce?
___________________________________________
e. If the two individuals above (EETT and eett) produce offspring, what would
be the expected genotypes and phenotypes of their offspring?
Genotypes ______________
Phenotypes __________________

In comparison to the study of heredity in plants, such as corn and garden pea,
however, where organisms can be crossed under well-controlled conditions in a
laboratory or an experimental field setting, where large numbers of progeny are
produced – allowing relatively easy and valid statistical analysis of the data – and no
serious ethical concerns are raised regarding selection of mating partners to match the
considered scientific questions, the study of inheritance of human traits is much more
difficult due to reasons as outlined below:

First of all, scientists can only study and analyze the result of matings (‘crosses’) that
have already occurred. Secondly, matings cannot – due to mandated and
understandable ethical reasons – be controlled and lastly, the numbers of human
individuals is very limited – a human geneticist normally deals with small family units

These limitations and difficulties often force geneticists to study human heredity using
unique tools of which pedigree (= family history) analysis and restriction fragment
length polymorphism (RFLP) analysis are the most important one, both of which you
will be studying in the second section of this “Human Genetics” lab
- while “classical” pedigree analysis has been used since the beginning of modern
genetics, the more sophisticated RFLP method which allows more detailed
genotypic analysis of human genetic traits is only beginning to be routinely used in
human genetic and clinical analysis
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