Name: ___________________________________________________ Date: ___________ Block: _________
Review of Key Vocabulary and Types of Punnett Squares
Video One: Introduction to Heredity
https://www.khanacademy.org/science/biology/heredity-and-genetics/v/introduction-to-heredity
Who is the father of classical genetics? ______________________________________________
Remember we are working on the simplicity assumption that some traits have an all or nothing
property. The example we are using is eye color:
Blue Eyes: _____ Brown Eyes: ______
Important Vocabulary:
What is an allele? __________________________________________________________________
What is a gene? ___________________________________________________________________
Homologous Chromosomes:
The diagram below gives us a visual of a pair of homologous chromosomes that code for the same
trait. One of those chromosomes came from mom and other from dad when the gametes united
during fertilization. In this case that trait is eye color.
Homologous Chromosomes:
Genotype:
B b: _______________
b b: _______________
Answer the following questions:
1. How do we know if the offspring will have brown or blue eyes?
2. Explain the difference between genotypes and phenotypes.
3. What mistake does Sal make around minute 9:08 in the video?
4. Can you look at someone’s eye color and know their genotypes? Explain.
Setting up a Punnett square
Dad and Mom are both heterozygous for brown eyes. What would a Punnett square look like for this
cross?
___________
x
____________
Moms Alleles
Genotype:
Dads Alleles
B
B
b
BB
Phenotype:
b
What is the probability that they will produce a heterozygous child?
Remember that we can use Punnett squares to make predictions but that doesn’t guarantee the outcome.
Video Two: Punnett square fun
https://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun
1. Where does the term Punnett come from? What scientist are they named after?
Incomplete Dominance: meaning the mixing or ________________ of the traits. The rules will
change because there is not a dominant or recessive allele in this situation.
Key:
R = Red
Cross:
RW
x
W = White
RW = Pink!
RW
How many of the offspring would be
pink in color? Why?
Blood Types: This is combination of codominant (which means that both alleles will be expressed)
and recessive alleles.
Alleles for Blood:
A,
B,
and
O (recessive)
Codominant
Blood Types:
A,
B,
O,
and
AB
What is the probability of having a child with A-blood type when you cross a parent who has AB-blood
with one that has A-blood?
Cross:
AO
x
AB
Dihybrid Crosses: this is a cross where you are following two traits at one time.
Key:
Eye Color
Size of Teeth
B = Brown Eyes
b = Blue Eyes
T = Big Teeth
t = Small Teeth
What is the key assumption?
Two pairs of Homologous Chromosomes:
Big Teeth
Eye Color
Size of Teeth
BbTT
Brown Eyes
Explain what would happen if the traits were on the same
chromosome?
Cross two individuals who are both hybrids (heterozygous) for both eye color and size of teeth.
Cross:
BbTt
x BbTt
For ease, always keep the traits in the same order (eye color first and tooth size second) and within
each trait put the dominant allele before the recessive allele.
Genotype:
Phenotype:
________ Brown eyes and Large Teeth
________ Brown eyes and Small Teeth
________ Blue eyes and Large Teeth
________ Blue eyes and Small Teeth