Using Punnett Squares to find phenotypes

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					     Name_______________________________________________________ Date___________________ Per _____

                                      Using Punnett Squares to find Phenotypes
Background Info: A Punnett Square is a tool used to visualize all the possible combinations of alleles
from the parents. A pair of genes (the “genotype”) controls a trait (the “phenotype”). One pair of genes
comes from each parent. The mother’s genes (alleles) are placed on the left and the father’s genes on
the top. (this shows a “cross” between these two parents). Each of the 4 squares inside represents the
offspring that these 2 parents could have. To be more specific, each inner square shows what genotypes
each of the possible offspring could have for the trait in question, by showing the different possible gene
combinations.

1. Construct a Punnett square for eye color. The genes for eye color are E/e. “E” stands for
the dominant gene and “e” stands for the recessive gene. Brown, black, green or hazel eyes
are the dominant trait. Blue or gray eyes are the recessive trait. The mother has brown eyes
 with genotype Ee and the father has blue eyes.
Questions:
What is the father’s genotype for eye color? ________
Out of 4 children, what are the chances of these 2 parents having brown-eyed children? ________
Out of 4 children, what are the chances of these 2 parents having blue-eyed children? ________

2. Construct a Punnett square for the sex or gender of a person (X and Y). All males
 have the XY genotype and all females have the XX genotype. (neither X or Y is dominant).
Complete the Punnett square to find out the chances of male and female offspring being
born (obviously, to male and female parents!)
Questions:
What are the chances of a male being born? ________
What are the chances of a female being born? ________
Who determines the sex of the children, the male or the female? and how do you know this?
________________________________________________________________________________________________

3. Blood type is controlled by 3 genes; A, B and O, as shown in the chart. With blood type, capitals are always used. A &
B are both dominant over O.

           Phenotype         Genotype:    A female with blood type A (genotype AO) marries a
           (blood type):                  male with blood type B (genotype BO). Fill in the
      A                    AA or AO       Punnett square to show this cross.
      B                    BB or BO
      O                    OO
      AB                   AB
Questions:
List all the possible blood types (phenotypes) that their children could have.
What are the chances of their children having blood type A? ________
What are the chances of their children having blood type B? ________
What are the chances of their children having blood type AB? ________
What are the chances of their children having blood type O? ________

4. Fill in the Punnett square for the following questions
a. If two people with blood type 0 were to marry, what would be the chances of their having
children with blood type A? ________
b. What would be the chances of these parents-to-be having children with blood type O? ________



5. In guinea pigs, the fur color is black for dominant (B) and white is recessive (b). If a hybrid
male (Bb) is crossed with a hybrid female what is the probability that an offspring would be
black?________________ White? _________________
For each of the remaining questions:
a. put the parents’ alleles on the Punnett Square
b. fill in the genotypes of the offspring in the Punnett square
c. Write in the phenotypes and genotypes of the parents
d. Write in the % expected of the offspring phenotypes and genotypes


6. A cross between 2 heterozygous parents. Black fur (B) is dominant.
(white fur is recessive, b)

        c.

        d.


7. A cross between a homozygous dominant parent and a
homozygous recessive parent. Red feathers is dominant, R.
(recessive is blue feathers, r)

        c.

        d.


8. A cross between 2 homozygous recessive plants.
Tall stems, T is dominant. (recessive is short stems, t)

        c.

        d.



9. A cross between 2 homozygous dominant plants.
Green seed color, G is dominant. (recessive is yellow seed color, g)

        c.

        d.



10. A cross between a heterozygous plant and a
dominant homozygous plant. White flowers (W) is dominant.
(recessive is yellow flowers, w)

        c.


        d.



11. A cross between a heterozygous person and a homozygous
recessive person. Widow’s peak, W is dominant. (recessive is
no widows peak, w)
        c.

        d.