Humans display numerous traits controlled by a variety of genes. Some of these traits are determined by two alleles, one dominant and one recessive. Other traits may be determined by three or more alleles, sex-linked, etc., or by a combination of environmental factors. Dominant and recessive traits are studied in this activity, utilizing the Hardy-Weinberg scheme, whereby evolution can be viewed as changes in the frequency of an allele in a population of organisms. This indicates that no matter how many times alleles are segregated into different gametes by meiosis and united in different combinations by fertilization, the frequency of each allele in the gene pool will remain constant if the following conditions are met: the breeding population is large; mating is random; there are no mutations of alleles; no differential migration occurs; and there is no selection.
Provided with a class gene pool, learners will be able to determine the frequency of specific alleles and genotypes by using the Hardy-Weinberg formula.
Materials:
Color Vision Test - At this web site, there are 31 different colorblindness tests that may be used to determine if a person is colorblind. The test generates a percentage.
The Hardy-Weinberg Equilibrium - This web site is from John W. Kimball's Biology Pages. It presents the Hardy-Weinberg model and contains additional useful genetics information.
Obtain a copy of the Phenotype Class Traits checklist. Use this table to observe and identify your phenotypic traits.
Using capital or small letters, record your phenotype in the table into the column labeled Personal Phenotype.
Transfer your personal phenotype data to the chalkboard so that others may compile and calculate the remaining table information.
Record your classmates' data onto your table into the appropriate columns.
Determine the percentage of the students that demonstrate each recessive trait.
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x100 |
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Calculate the frequency for the recessive allele (trait) for each of the ten traits. Use the example below as a guide.
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Example Problem: Given a population that has 30% having the homozygous recessive, determine the frequency of one allele (a). |
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Background Information
a = one allele Let's say 30 % have recessive trait (homozygous recessive). |
Then... |
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aa = 30% |
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q2 = 0.30 |
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q = 0.30 q1/2= 0.55 |
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a = .55 |
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Solution: The frequency of one allele (a) is 0.55. |
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Use the following example to determine the dominant allele frequency for each of the ten traits.
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Example Problem: Given information from step six, determine the frequency of the dominant allele (A). |
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Background Information
qrecessive allele = 0.55 p + q = 1 or p = 1 - q
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Then... |
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p = 1 - q |
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p = 1 - 0.55 |
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p = 0.45 or A = 0.45 |
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Solution: The frequency of one allele (A) is 0.45. |
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One can then square 0.45 to determine the percentage of individuals that would have the homozygous dominant. In this case it would be about 20% of the population. |
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Use the example below to determine the heterozygous frequency for each of the ten traits.
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Example Problem: Given information from step six and seven, determine the percent of individuals that are carriers of this specific trait. |
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Background Information From steps six and seven you have... p = 0.45 and q = 0.55 Diploid Combinations = 2pq = Aa |
Then... |
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Combinations = 2pq |
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Combinations = 2 x 0.45 x 0.55 = 0.50 |
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p = 0.45 or A = 0.45 |
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Solution: The frequency of the heterozygous trait(Aa) = 0.50 |
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This would indicate that 50% of the population are carriers of this trait. |
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Depending on access to computers and teacher preferences, you may download the attached supplement Phenotype Calculator to check your calculations. It is an Excel spreadsheet file.
Use the attached form to share findings with students from other locations.
Answer the "Engaging Questions" found in the Teacher's Guide of this lesson.
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