Genetic Variation Activity
An individual’s trait that is passed on from generation to generation is called the process of heredity.
This simply means that these characteristics are passed from parent to offspring. Human characteristics
are expressed in two different ways. One is genotype and the other is phenotype. Genotype is the
genetics “make-up” of an individual. The genes, which are the units of heredity, make up a genotype.
Phenotype is the physical trait one can observe. This is the result of the genotype.
Genes, which are made up of alleles can be found on the chromosomes in a cell. These alleles, when
paired together, determine whether a genotype is heterozygous or homozygous. Heterozygous means
that there are two alleles that are not the same (Xx). Homozygous means that the alleles are the same
(XX). Keep in mind, in nature; these combinations of alleles happen by chance.
The alleles carry the information as to whether or not a dominant or recessive trait is present. An allele
that carries a dominant trait is represented by a capital letter. An allele that carries a recessive trait is
represented by a lower case letter. When the genotype of allele pairs are expressed as homozygous or
heterozygous with dominancy present, the phenotype is portray the dominant physical characteristic. If
the genotype has no dominant alleles present and is homozygous recessive, then the phenotype will be
expressed by the recessive physical characteristic.
In some cases, the genotype is heterozygous but neither the dominant nor the recessive phenotype or
physical characteristic, is presented. This is called an incomplete dominance or co-dominance. In
incomplete dominance, it simply means that the offspring has a “blend” of two physical characteristics.
For example, a red flower parent and a white flower parent will produce a pink flower offspring,
whereas co-dominance shows both traits. For example, a red flower and a white flower will produce a
flower that is red with white spots. Sometimes characteristics are found on many genes. This causes a
blend of traits as well. An example of this is skin color.
In humans, the sex of an individual is determined by the combination of two sex chromosomes. One
chromosome is donated by the female parent, found in the egg, and the other chromosome is donated
from the male parent, found in the sperm. Persons with two X chromosomes are female (XX) while
those with one X and one Y are males (XY).
With this activity, you will see how different combinations of alleles produce different characteristics.
Pre-Question: How are traits inherited?
_________________________________________________________________________________
__________________________________________________________________________________
Activity Discussion Questions
1. A coin will be used to determine genotype in this activity. What does a single side of the coin
represent? __________________________________________________________________
2. What are the chances that a coin will land heads up? _______________________________
______________________________________________________________________________
3. How is a coin toss like the selection of a particular allele? ____________________________
______________________________________________________________________________
4. Can you accurately determine a person’s genotype by observing his or her phenotype?
_______________________________________________________________________________
General Procedure
Flip a coin to determine the dominant and recessive alleles for your baby. If your coin lands on HEADs, it
is a dominant trait. If your coin lands on TAILs, it is a recessive trait. Remember, dominant alleles are
written as a capital letter and recessive alleles are written as a lower case letter. Record results on your
data worksheet. Be sure to use to correct letters from the Variation sheet (attached).
Draw one popsicle stick from the cup to determine the blood type. Record your information on your
data sheet.
Assessment Questions
1. What would the offspring height be if he/she has the genotype HHGGTT? ________________
________________________________________________________________________________
2. Would the offspring have the same height if he/she was born in a country that suffered from
malnourishment? Explain why. ______________________________________________________
_________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________