Name _______________________________________
Section 6.5: Traits and Probability
Date __________________
Main Ideas:
 Punnett squares illustrate genetic crosses
 A monohybrid cross involves one trait
 A dihybrid cross involves two traits
 Hereditiy patterns can be calculated with probability
Vocabulary:
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Punnett Square
Mononhybrid cross
Dihybrid cross
Test cross
Probability
Law of Independent
assortment
1. What is the likelihood of flipping a coin and it coming up a head or a tail? _________________
2. What is the likelihood of you being a boy or a girl? __________________________
3. If you are a hybrid (heterozygous) for being right handed, what is the likelihood of producing a sex cell
that has the right handed gene in it? _______ The left handed gene? ____
4. What is a Punnett square?
5. What goes on the outside of a Punnett Square?
6. Fill in the Punnett square shown below which will help to predict the likelihood of two individuals who
are hybrids for having allergies (Having allergies is a dominant trait so we will use an “A” for the gene.
Alleles of Parent 1
A
Alleles
of
Parent 2
7.
8.
9.
a
A = Allergies
A = No allergies
A
a
How many of each genotype is possible for the offspring? _____ AA: ____Aa: ______aa
How about the possible phenotypes? ________Allergies: ________ no allergies
Use the Punnett square to the right to show what would happen for
the same trait of having allergies, if one parent was a hybrid and
the other parent was pure or homozygous recessive for not having
allergies.
Possible Genotype ratio? _____AA: _____Aa: _____aa
Possible Phenotype ratio? ______ Allergies: ______ no allergies
10. For each of the following traits, provide the symbols for the key, show the parent cross, do the Punnett
square and then give the phenotype and genotype ratios.
Trait: Hand Preference in humans. Being right handed is dominant to left hand preference.
___ = Right Hand preference
___ = Left Hand preference
1. Cross two individuals with one being pure or homozygous dominant ____and the other being a
hybrid or heterozygous for being right handed ____.
Parent cross: ____ x ____
Possible phenotypes: _____ right handed: ____ Left handed
Possible genotypes: _____ RR: ____Rr: _____rr
For the same trait, cross a person who is pure for being right handed ____ with a lefty ___.
Parent cross: _____x ____
Possible phenotypes: _____ right handed: ____ Left handed
Possible genotypes: _____ RR: ____Rr: _____rr
Trait: Earlobe position: In humans, having free earlobes is dominant to having an attached earlobe
_____ = Free Earlobes
_____ = Attached Earlobes
2. Cross a two people who both are hybrids ____ x ___ _for having free earlobes.
Possible phenotypes: _____ Free Earlobes: ____ Attached
Possible genotypes: _____ FF: ____Ff: _____ff