BIOL209: General Genetics Laboratory Mendelian Inheritance in Humans PRE-LAB ASSIGNMENT: Students are expected to read all pages before coming to the lab to complete the experiments. Print this entire lab packet and bring it to the laboratory. Objectives: After completing this laboratory assignment, students will be able to: 1. Observe some single-gene genetic traits in humans. 2. Solve problems involving Punnett squares and pedigrees Modern genetics began with the work of Gregor Mendel and his study of pea plants. Mendel observed patterns in the number of each phenotype (physical appearance) of offspring from different parents. Mendel described genetic concepts that are used today to explain simple heredity (what traits are passed from one generation to the next) and variation (the differences between parents and their offspring). Through his experiments, Mendel determined that there can be multiple forms of the same gene. These alternate forms of genes, which are called alleles, code for slightly different expressions of a genetic trait. He recognized that some alleles exhibited dominant tendencies and others, recessive tendencies. When a dominant allele combined with a recessive allele, the dominant allele was expressed in the phenotype. Following the system that Mendel used in his experiments, a dominant allele is represented with a capital letter, and a recessive allele is represented with a lowercase letter. For decades, teachers and professors have used a few classic human traits to demonstrate the concepts of simple autosomal inheritance. In this activity, you will observe the phenotypes of people in your class. You will apply your results, along with research findings, to predict whether each trait follows patterns of simple autosomal inheritance. Mendelian Laws apply to the simple autosomal inheritance that Gregor Mendel studied, but these laws do not always apply to more-complex modes of genetic inheritance. 1. The Law of Segregation: Inherited traits are determined by genes, with two copies of each gene. Parental genes are randomly separated and segregated into each sex cell (gamete) with one copy of each gene per gamete. Offspring inherit one copy of each gene from each parent. 2. The Law of Independent Assortment: The inheritance of one trait is not dependent on the inheritance of another. It turns out that some genes, and therefore some traits, are linked. Therefore, they are not assorted independently. Genes in close proximity to one another on the same chromosome are, in fact, more likely to be inherited together. 3. The Law of Dominance: If the inherited genes have multiple alleles, the dominant allele will determine the phenotype of the organism. In fact, some alleles are codominant, meaning that multiple alleles contribute to the phenotype of the individual. Traits may have more than two alleles for the same gene. Furthermore, multiple genes may contribute to the phenotype of one trait. Instructions This lab i.

1. BIOL209: General Genetics Laboratory
Mendelian Inheritance in Humans
PRE-LAB ASSIGNMENT:
Students are expected to read all pages before coming to the lab
to complete the experiments.
Print this entire lab packet and bring it to the laboratory.
Objectives:
After completing this laboratory assignment, students will be
able to:
1. Observe some single-gene genetic traits in humans.
2. Solve problems involving Punnett squares and pedigrees
Modern genetics began with the work of Gregor Mendel and his
study of pea plants. Mendel observed patterns in the number of
each phenotype (physical appearance) of offspring from
different parents. Mendel described genetic concepts that are
used today to explain simple heredity (what traits are passed
from one generation to the next) and variation (the differences
between parents and their offspring). Through his experiments,
Mendel determined that there can be multiple forms of the same
gene. These alternate forms of genes, which are called alleles,
code for slightly different expressions of a genetic trait. He
recognized that some alleles exhibited dominant tendencies and
others, recessive tendencies. When a dominant allele combined
with a recessive allele, the dominant allele was expressed in the
phenotype. Following the system that Mendel used in his
experiments, a dominant allele is represented with a capital
letter, and a recessive allele is represented with a lowercase
letter.
For decades, teachers and professors have used a few classic
human traits to demonstrate the concepts of simple autosomal
inheritance. In this activity, you will observe the phenotypes of

2. people in your class. You will apply your results, along with
research findings, to predict whether each trait follows patterns
of simple autosomal inheritance.
Mendelian Laws apply to the simple autosomal inheritance that
Gregor Mendel studied, but these laws do not always apply to
more-complex modes of genetic inheritance.
1. The Law of Segregation: Inherited traits are determined by
genes, with two copies of each gene. Parental genes are
randomly separated and segregated into each sex cell (gamete)
with one copy of each gene per gamete. Offspring inherit one
copy of each gene from each parent.
2. The Law of Independent Assortment: The inheritance of one
trait is not dependent on the inheritance of another.
It turns out that some genes, and therefore some traits, are
linked. Therefore, they are not assorted independently. Genes in
close proximity to one another on the same chromosome are, in
fact, more likely to be inherited together.
3. The Law of Dominance: If the inherited genes have multiple
alleles, the dominant allele will determine the phenotype of the
organism.
In fact, some alleles are codominant, meaning that multiple
alleles contribute to the phenotype of the individual. Traits may
have more than two alleles for the same gene. Furthermore,
multiple genes may contribute to the phenotype of one trait.
Instructions
This lab is designed to demonstrate genetics, or the study of
how heritable characteristics are passed from generation to
generation. Genetic traits are determined by genes, or small
segments of DNA carried on chromosomes that determine
physical characteristics. This exercise demonstrates how

3. different alleles of the same gene segregate and reassort
(separate and come together) in a population.
Part I: Observing Mendelian Inheritance in Human Traits
1. Students will work in groups of two to complete the
assignments.
2. Every person will submit an individual lab report for this lab.
3. Mark your appropriate phenotype for each trait on the chart.
4. Determine your corresponding genotype for each trait; if
dominant, use the heterozygous genotype.
Human Genetic Traits
A. Facial Dimples: Dimples, or indentations, at the corner of the
mouth are a dominant trait.
B. Bent little finger: A dominant allele causes the last joint of
the little finger to dramatically bend inward toward the 4th
finger. Lay both hands flat on a table relax your muscles, and
note whether you have a bent or straight little finger.
C. Eye Color: Brown pigmented irises are dominant. The
absence of brown pigment results in blue eyes, which is
recessive. Hazel or green eye color is the result of a second
gene that produces a yellow pigment. Hazel eyes have both
brown and yellow iris pigment, while green eyes have both the
recessive blue iris and dominant yellow pigment. For our
purposes, assess only the presence of absence of brown
pigment.
D. Free Earlobes: Free earlobes are dominant over attached
earlobes. Read the introduction to Chapter 9 for an explanation
of how this trait is produced during fetal development.
E. Mid-digital Hair: The presence of hair on the middle joint of
the finger is a dominant trait. Hair may not be present on all of
your fingers, but if you have hair on even one finger, you are

4. dominant.
F. Hand clasping: When the hands are clasped (without thinking
about it!), most people place their left thumb on top of their
right.
G. Widow's Peak: A distinctive downward point of the frontal
hairline is a dominant trait known as a widow's peak. If you
have a straight hairline, you are recessive for this trait.
H. Tongue Rolling: The ability to roll the tongue upward from
the sides is a dominant trait. For some reason, people who
exhibit this trait seem to think it is a desirable thing to do. As
far as anyone knows, tongue rolling has no obvious anatomical
or physiological advantage or disadvantage.
I. Chin cleft: A prominent cleft in the chin is inherited as the
dominant phenotype. The cleft is due to the bond structure
which underlies the Y-shaped fissure of the chin. Females
appear to be less conspicuously affected than males.
J. Hitchhiker's Thumb: The ability to bend the thumb backward
at least 45 is a dominant trait. The proper term for this is distal
hyperextensibility.
K. Handedness: Right-handedness is an autosomal dominant
trait.
L. Finger number: The number of fingers on the hand is
controlled by genes. Having more than 5 digits is dominant.
M. PTC Tasting: The ability to taste the chemical
phenylthiocarbamide, or PTC, is a dominant trait. Place a piece
of PTC paper on the back of your tongue. If you can detect this
chemical, it will have a bitter taste. If the paper does not taste
nasty to you, then you are recessive for this trait.

5. N. Relative Length of the Big Toe: If your big toe is shorter
than your second toe, you are dominant for this trait.
O. Palmaris Longus Muscle: The presence of this muscle is a
dominant genetic trait. If you have this muscle you will have
three wrist tendons. To determine this, clench your fist tightly
and flex your hand toward you. If you can see or feel three
tendons in your wrist, you have the long palmar muscle and are
dominant. If you have only two tendons, then you are recessive
for this trait.
Data Sheet
Class Data
Traits
Symbols
Dominant Phenotype
Your phenotype
Your genotype
Dom
Rec
1. Facial dimples
D, d
Dimples
d
2. Bent little finger
B, b
Bent little finger
b

6. 3. Eye Color
E, e
Brown eyes
E
4. Free ear lobe
F. f
Free ear lobe
F
5. Mid-digital hair
H, h
Presence of hair
h
6. Hand clasping
L, l
Left on top
L
7. Widow’s peak
W, w
Widow’s peak
w

7. 8. Tongue Rolling
T, t
Tongue roll
T
9. Chin cleft
C, c
Cleft in chin
c
10. Hitchhiker’s Thumb
H, h
Straight
(180°)
h
11. Handedness
R, r
Right
R
12. Finger number
S, s
Six-digits
s

8. 13. PTC Tasting
P, p
Tasting
P
14. Big Toe Length
G, g
Longer Big toe
g
15. Palmaris Longus Muscle
M, m
Three tendons
m
Questions
1. Did you have mostly dominant or recessive traits?
Recessive
2. Compare your findings with other students.
a. For which trait were most students dominant?
b. For which traits were most students recessive?
Part II: Mendelian Genetics: Monohybrid Crosses

9. A monohybrid cross is the genetic transmission of a single trait.
For this exercise, you will “mate” (exchange gametes) with the
person listed and determine the genotypes and phenotypes of the
offspring that could result from each mating, or “cross”.
1. Complete a Punnett Square using your genotype and the
given genotype. Calculate the probability of all the different
possible genotypes and phenotypes of your offspring in
percentages.
a. Widow’s Peak: Yours_____Ww___________ & your
partners: ww
b. Tongue Rolling: Yours_____TT___________ & your partners
Tt
c. Hand Clasping: Yours______LL__________ & your partners
LL

10. 2. Two people who are heterozygous for tasting the chemical
PTC marry. List the genotypes possible for their children
regarding the tasting of PTC. Show your work.
Part 2: Dihybrid Crosses
1. Alfred is heterozygous for tongue rolling and has five
fingers. Alfreda, his wife, cannot roll her tongue and is
heterozygous for polydactyly.
a. What is Alfred’s genotype?
b. What is Alfreda’s genotype?
c. What are Alfred’s possible sperm with regard to these two
traits?

11. d. What are Alfreda’s possible eggs with regard to these two
traits?
e. What is the probability that their first child will not roll its
tongue and will have the normal number of fingers?
Part 3: Pedigrees
1. Determine the mode of inheritance.
2. Label the generations, genotypes and correct symbols (if
applicable)