NAME: Date:
Lesson 6.2: True or False
Write true if the statement is true or false if the statement is false.
_____ 1. The rules of probability apply to genetics.
_____ 2. If an individual has a Gg genotype, half of his gametes should have the G allele, and the other half
should have the g allele.
_____ 3. A Punnett square is a chart that allows you to easily determine the expected genotypes in the offspring
of two parents.
_____ 4. In a cross between two homozygous dominant individuals, 25% of the offspring may have the
recessive phenotype.
_____ 5. A parent cell makes gametes through the process of mitosis.
_____ 6. It is entirely likely for a gene to have more than two alleles.
_____ 7. Incomplete dominance occurs when the recessive allele is not completely dominant.
_____ 8. Your height and skin color are not just due to your genes.
_____ 9. In a cross between an individual homozygous dominant for two characteristics and an individual
homozygous recessive for the same characteristics, all of the F1 offspring will have the dominant
phenotypes.
_____ 10. All genetics is fairly straightforward and follows the patterns Mendel observed in pea plants.
_____ 11. Codominance occurs when, essentially, there is no recessive allele.
_____ 12. If one parent is MM and the other parent is mm, the only possible phenotype of their offspring is Mm.
_____ 13. The probability of inheriting either an A, B, or O allele for blood type from your parent is 33.33%.
_____ 14. In any cross between two heterozygous parents, half the offspring should have the dominant
phenotype and half the offspring should have the recessive phenotype.
_____ 15. When you toss a coin in the air, it should turn up tails 50% of the time.
Lesson 6.2: Critical Reading
Read these passages from the text and answer the questions that follow.
Using a Punnett Square
A Punnett square is a chart that allows you to easily determine the expected percents of different genotypes in
the offspring of two parents. An example of a Punnett square for pea plants is shown below. In this example,
both parents are heterozygous for flower color (Bb). The gametes produced by the male parent are at the top of
the chart, and the gametes produced by the female parent are along the side. The different possible
combinations of alleles in their offspring are determined by filling in the cells of the Punnett square with the
correct letters (alleles).
Punnett Square. This Punnett square shows a cross between two heterozygotes. Do you know where each
letter (allele) in all four cells comes from?
Predicting Offspring Genotypes
In the cross shown in the figure above, you can see that one out of four offspring (25 percent) has the
genotype BB, one out of four (25 percent) has the genotype bb, and two out of four (50 percent) have the
genotype Bb. These percents of genotypes are what you would expect in any cross between two heterozygous
parents. Of course, when just four offspring are produced, the actual percents of genotypes may vary by chance
from the expected percents. However, if you considered hundreds of such crosses and thousands of offspring,
you would get very close to the expected results — just like tossing a coin.
Predicting Offspring Phenotypes
You can predict the percents of phenotypes in the offspring of this cross from their genotypes. B is dominant
to b, so offspring with either the BB or Bb genotype will have the purple-flower phenotype. Only offspring with
the bb genotype will have the white-flower phenotype. Therefore, in this cross, you would expect three out of
four (75 percent) of the offspring to have purple flowers and one out of four (25 percent) to have white flowers.
These are the same percents that Mendel got in his first experiment.
Questions
You may use Punnett squares to answer the following questions.
1. What are the percentages of genotypes you would expect in any cross between two heterozygous parents?
Use the letters B and b in your answer.
2. What are the percentages of phenotypes you would expect in any cross between two heterozygous parents?
Use the genotypes and phenotypes in the reading above.
3. Predict the percentage of genotypes you would expect in any cross between a homozygous dominant parent
and a homozygous recessive parent.
4. Predict the percentage of phenotypes you would expect in any cross between a homozygous dominant parent
and a homozygous recessive parent.
5. Predict the percentage of genotypes and phenotypes you would expect in any cross between a heterozygous
parent and a homozygous recessive parent.
Lesson 6.2: Multiple Choice
Circle the letter of the correct choice.
1. What is the inheritance pattern when both alleles are expressed equally in the phenotype of a
heterozygote?
a. multiple alleles
b. incomplete dominance
c. codominance
d. polygenic characteristics
2. What is the inheritance pattern when the dominant allele is not completely dominant?
a. multiple alleles
b. incomplete dominance
c. codominance
d. polygenic characteristics
3. What is the inheritance pattern associated with the ABO blood type in humans?
a. multiple alleles
b. incomplete dominance
c. codominance
d. polygenic characteristics
4. In a cross between a homozygous dominant parent and a homozygous recessive parent, what is the
chance of the offspring having a heterozygous genotype?
a. 25%
b. 50%
c. 75%
d. 100%
5. In a cross between a homozygous dominant parent and a homozygous recessive parent, what is the
chance of the offspring having the dominant phenotype?
a. 25%
b. 50%
c. 75%
d. 100%
6. In a cross between a homozygous dominant parent and a heterozygous parent, what is the chance of
the offspring having a heterozygous genotype?
a. 25%
b. 50%
c. 75%
d. 100%
7. In a cross between a homozygous dominant parent and a heterozygous parent, what is the chance of
the offspring having the dominant phenotype?
a. 25%
b. 50%
c. 75%
d. 100%
8. In a cross involving two heterozygous parents, which is the chance of the offspring having the
dominant phenotype?
a. 25%
b. 50%
c. 75%
d. 100%
Lesson 6.2: Vocabulary I
Match the vocabulary word with the proper definition.
Definitions
_____ 1. occurs when the dominant allele is not completely
dominant Terms
_____ 2. closely associated with appearance a. ABO blood type
b. allele
_____ 3. an example of a characteristic due to multiple alleles
c. codominance
_____ 4. controlled by more than one gene d. dominant allele
e. incomplete dominance
_____ 5. the expressed allele in a heterozygote
f. meiosis
_____ 6. cell division involved in gamete formation g. phenotype
_____ 7. used to determine the expected percents of different h. polygenic characteristic
genotypes in offspring i. probability
_____ 8. an alternative form of a gene j. Punnett square
k. recessive allele
_____ 9. chance that a certain event will occur
_____ 10. only expressed when the other allele is absent
_____ 11. occurs when both alleles are expressed equally in the phenotype of the heterozygote
Vocabulary II
Fill in the blank with the appropriate term.
1. If you toss a coin twice, you might expect to get ____________ head and ____________ tail.
2. A Punnett square allows you to determine the expected percents of different _______________ in the
offspring of two parents.
3. ____________ is when both alleles are expressed equally in the phenotype of the heterozygote.
4. ____________ is the chance that a certain event will occur.
5. Paired alleles always separate and go to different gametes during ____________.
6. If one parent is heterozygous and the other parent is homozygous recessive, the probability that their child
will be homozygous recessive is ____________.
7. If a parent has a Dd genotype, the probability of their child inheriting a d allele from that parent is
____________.
8. ____________ dominance occurs when the dominant allele is not completely dominant.
9. Sometimes an individual's phenotype is not just due to his or her genes, but also ____________ influences.
10. A cross between a homozygous dominant individual and a homozygous recessive individual will always
result in a ____________ individual.
11. ABO blood type in humans is a characteristic due to multiple ____________.
12. When a Bb pea plant forms gametes, the B and b alleles segregate and go to different _________________.
Lesson 6.2: Critical Writing
Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.
Draw a Punnett square of a cross between a homozygous dominant individual and a heterozygous individual.
