Overview
Procedure
Pair up with someone. (Or you can do this by yourself--you will be both parents!.)
One person will be the mother and one the father (this is pretend, so actual sex is not important!).
Each parent should have two coins to flip.
Determine the sex of the child by flipping one coin. Which parent should flip the coin (that is, determine the sex of the offspring)?
Give your child a name.
Heads will represent the dominant allele (capital letter)
Tails will represent the recessive allele (small case letter).
First, each parent needs to flip two coins to determine their genotype for each trait (because a genotype consists of 2 alleles). The possible outcomes of flipping two coins are: HH, HT, or TT. In genetics, we represent the two alleles (dominant and recessive) as a capital and small case of the same letter, so the outcomes of flipping two coins translated into genetics symbols, for gene A, is:
HH = AA
HT or TH = Aa
TT = aa
(where H=heads and T=tails).
For each trait, enter the mother’s genotype (AA, Aa, or aa) into the Maternal Genotype column.
Enter the father’s genotype in the Paternal Genotype column.
Each parent determines which one of their two alleles they will pass on to their child.
If a parent is AA or aa, this is easy because they can only pass on one allele (either an A or an a depending).
Simply enter this allele in the Child’s Genotype column.
However, if a parent is Aa, then they must flip a coin again to determine which allele they pass on to their child.
Record the allele that is passed on to the offspring from each parent in the Child’s Genotype column. Remember, the child gets only one allele from each parent.
Look up the phenotype that goes with the genotype of the child. These are shown in the illustrations of the traits.
Record the phenotype in a table.
Polygenic Traits: some traits are controlled by more than two genes and thus have a more complex phenotypic pattern. Skin color and eye color are examples of polygenic traits in this exercise.
Skin Color
Skin color is controlled by a number of genes that function additively, something like molecular voting. To simulate the many genes involved in skin color, each parent should flip their coin 4 times. Record how many heads are thrown. Eight heads means very dark skin. Zero heads means very pale skin. Here is the model for skin color:
Eight dominant alleles = very dark skin
Seven dominant alleles = very dark skin
Six dominant alleles = dark skin
Five dominant alleles = dark brown skin
Four dominant alleles = brown skin
Three dominant alleles = light brown skin
Two dominant alleles = pale skin
One dominant allele = very pale skin
Zero dominant alleles = albino (lack of any pigment)
Eye Color
There are six basic eye colors in humans, with many gradations due to the influence of various genes and the environment. Eye color depends mostly on how much of the brown pigment melanin is in the iris, the colored part of the eyes. The more pigment, the darker the eyes. Truly black eyes do not exist. Eyes that appear black are simply very dark brown. Blue eyes appear blue due to scattering of light (the same reason the sky appears blue). Green and amber eyes are produced by the deposition of an additional yellow pigment (lipochrome). Hazel eyes have flecks of other colors (gold, green, brown, orange) as opposed to amber which are a more uniform gold or copper color.
While numerous genes may influence eye color, two main genes (OCA2 and HERC2) appear to be primarily responsible for the phenotype.
In this simulation we will call these two genes, A and B. For each gene, each parent must flip once, so the offspring gets two copies of each gene. Determine eye color based on this model:
AABB = brown
AABb = brown
AaBB = brown
AaBb = amber
AAbb = hazel
aaBB = green
Aabb = blue
aaBb = blue
aabb = gray