Download Complete Dominance (Information)

Complete Dominance (Information):
Section 1: Monogenic vs. Polygenic
Many traits observed in individuals are
polygenetic traits, meaning that the trait is
controlled by more than one gene. The following
are a few examples of polygenic traits in humans:
• Skin color
• Foot size
• Hair color
• Height
• Eye color
• Nose length
Predicting the phenotypes of offspring for polygenic traits can get
complicated, thus we will be primarily focusing on monogenic traits –
traits that are controlled by single genes – in this class.
Section 2: EXAMPLES OF COMPLETE DOMINANCE
WIDOW’S PEAK is an example of a
Widows Peak
monogenic trait that displays complete
dominance. This means that if the allele for
having widows peak is present, whether
homozygous or heterozygous, then the
individual would display a widow’s peak.
Geneticists use capital letters for a
dominant trait and lower case letters for a
recessive trait. We will use the letter “W” to
represent a dominant allele for widow’s peak.
Unattached Earlobe
EARLOBE ATTACHMENT is another
example of a monogenic trait that displays
complete dominance. Having unattached
earlobes is dominant to having attached
earlobes.
Complete Dominance (Questions):
Section 1: Monogenic vs. Polygenic
1) Describe the difference between monogenic and polygenic traits.
2) List some examples of polygenic traits in your journal
3) Why will we be focusing mainly on monogenic traits?
Section 2: Complete Dominance Examples
1) Describe a dominant and recessive trait. When does the phenotype
show a dominant trait? When does a phenotype show a recessive
trait? Describe in terms of alleles and genotypes.
Widow’s Peak:
2) What percent of your class has a widow’s peak? (Show your work)
3) How many alleles will each individual have for widows peak? How
do you know? (hint: relate to gametes, zygotes and haploid, diploid)
4) What letter will you use to show widows peak and will it be a capital
or lowercase letter? Why?
5) How many different phenotypes for widow’s peak can an individual
have? Make a small table to show the genotypes , phenotypes and
labels (homozygous dominant, heterozygous, or recessive) for all
three combinations of alleles for widows peak.
Earlobe Attachment:
6) What percent of your class has unattached earlobes? (Show your
work)
7) Choose a letter to represent the alleles for earlobe attachment.
What will the capital and lowercase version of this letter stand for?
8) How many different phenotypes for earlobe attachment can an
individual have? Make a small table to show the genotypes ,
phenotypes and labels (homozygous dominant, heterozygous, or
recessive) for all three combinations of alleles for widows peak.