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6.2: Mendelian Inheritance

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Lesson 6.2: True or False

Name___________________ Class______________ Date________

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

Name___________________ Class______________ Date________

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? (Image courtesy of CK-12 Foundation and under the Creative Commons license CC-BY-NC-SA 3.0.)

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 percents of genotypes you would expect in any cross between two heterozygous parents? Use the letters B and b in your answer.

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2. What are the percents of phenotypes you would expect in any cross between two heterozygous parents? Use the genotypes and phenotypes in the reading above.

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3. Predict the percents of genotypes you would expect in any cross between a homozygous dominant parent and a homozygous recessive parent.

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4. Predict the percents of phenotypes you would expect in any cross between a homozygous dominant parent and a homozygous recessive parent.

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5. Predict the percents of genotypes and phenotypes you would expect in any cross between a heterozygous parent and a homozygous recessive parent.

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Lesson 6.2: Multiple Choice

Name___________________ Class______________ Date________

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?
    1. multiple alleles
    2. incomplete dominance
    3. codominance
    4. polygenic characteristics
  2. What is the inheritance pattern when the dominant allele is not completely dominant?
    1. multiple alleles
    2. incomplete dominance
    3. codominance
    4. polygenic characteristics
  3. What is the inheritance pattern associated with the ABO blood type in humans?
    1. multiple alleles
    2. incomplete dominance
    3. codominance
    4. 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?
    1. 25%
    2. 50%
    3. 75%
    4. 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?
    1. 25%
    2. 50%
    3. 75%
    4. 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?
    1. 25%
    2. 50%
    3. 75%
    4. 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?
    1. 25%
    2. 50%
    3. 75%
    4. 100%
  8. In a cross involving two heterozygous parents, which is the chance of the offspring having the dominant phenotype?
    1. 25%
    2. 50%
    3. 75%
    4. 100%

Lesson 6.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. occurs when the dominant allele is not completely dominant

_____ 2. closely associated with appearance

_____ 3. an example of a characteristic due to multiple alleles

_____ 4. controlled by more than one gene

_____ 5. the expressed allele in a heterozygote

_____ 6. cell division involved in gamete formation

_____ 7. used to determine the expected percents of different genotypes in offspring

_____ 8. an alternative form of a gene

_____ 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

Terms

a. ABO blood type

b. allele

c. codominance

d. dominant allele

e. incomplete dominance

f. meiosis

g. phenotype

h. polygenic characteristic

i. probability

j. Punnett square

k. recessive allele

Lesson 6.2: Vocabulary II

Name___________________ Class______________ Date________

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

Name___________________ Class______________ Date________

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.

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