# Part I Make a Punnett Square for each cross

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```					            Punnett Square Practice
Part I: Make a Punnett Square for each cross below. Black fur (B) is dominant to gray fur(b).

Directions: Highlight all words that are in bold – these are the genotypes of your parents!
Be sure to list the potential genotypes and phenotypes of the offspring with percents!

1. If the mother is homozygous recessive and the father is
homozygous dominant.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities.

2. If the mother is heterozygous, and the father is
heterozygous.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities

3. If the mother is heterozygous, and the father is
homozygous dominant.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities

4. If the mother is homozygous recessive, and the father
is heterozygous.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities
Part II: Lets do some more Punnett Square practice using flower traits.
Directions: Highlight all words that are in bold – these are the genotypes of your parents!
Be sure to list the potential genotypes and phenotypes of the offspring with percents!

You are experimenting with orchids, where red flowers are dominant over white flowers. (Use
the letter "R"). Make the following crosses:

1. Cross red homozygous orchids with white
homozygous orchids.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities

2. Cross heterozygous orchids with
heterozygous orchids.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities

3. Cross homozygous recessive orchids with
red heterozygous orchids.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities

4. Cross Red homozygous orchids with Red
heterozygous orchids.

a) What are the genotypes of the parents?

b) Write the genotype probabilities.

c) Write the phenotype probabilities
Part III: Now for more practice using traits from people.

Now look lets look at people, using eye color. Brown eyes are
dominant over blue/green. (Use the letter "B"). Make the
following crosses:

1. Mix two homozygous dominant parents
together.

a) Write the genotype
probabilities.

b) Write the phenotype
probabilities.

2. Mix two heterozygous parents together.

a) Write the genotype
probabilities.

b) Write the phenotype
probabilities.
3. Mix a homozygous dominant mom with a

a) Write the genotype
probabilities.

b) Write the phenotype
probabilities.
4. If Kevin has green (blue) eyes, and both his
parents have brown eyes, what must their
genotypes be? (Look at Part III #1-3 for help)

a) Write the genotype
probabilities.

b) Write the phenotype
probabilities.

Part IV: Are you now ready for a challenge?

"Sex-linked traits" come from genes that are located on the X
chromosome, and not on the y. (Remembers women are XX and men
are Xy). For example, baldness is a recessive sex-linked trait. Now
you write the allele letter as a part of the X chromosome, like this:

XB or Xb; y stays blank.
The players: B is not bald, b is bald.

Genotype:     XBXB            XBy           XBXb                   Xby         XbXb

Phenotype:    Not bald        Not bald      Not bald "carrier"     Bald        Bald
female          male          female                 male        female

Example:

Crossing a not bald female with a bald male results
in the following:

½ XBXb — Not bald
carrier female.

½ XBy — Not bald male.

1. Cross (mate) a bald male to a carrier
female.

a) Write the genotype
probabilities.
b) Write the phenotype
probabilities.
2. Cross a not bald male to a carrier female.

a) Write the genotype
probabilities.

b) Write the phenotype
probabilities.

If you’re a guy, which member of your family should you look at to tell if you
are going to go bald? Why? (Use a Punnett Square in your answer).

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