How do you know which trait is dominant?
Materials:
- Notebooks & pencils
- Printable
Student Worksheets
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Objectives:
This investigation is designed so that students can answer these questions:
How do you know which trait or which allele is dominant?
Also consider, how did scientists determine which trait is dominant in the first place?
Procedures:
This might be a good time to bring up the difference between determining which traits are dominant in humans and determining which traits are dominant in species in which mating or cross-pollinating experiments can be performed. Consider the method by which Gregor Mendel discovered dominant and recessive characteristics. He could selectively mate plants to generate the genotype he wished. Instead of using mating experiments as Gregor Mendel did we can use a process called pedigree analysis in order to study human genetics. In a way we will look backwards instead of forwards to determine what trait is dominant.
Have students work individually on this unless students do not have much access to parental information in which case working in groups of 2 or 3 will be satisfactory. After defining a pedigree analysis and showing students an example of a flow chart, students should each receive a copy of the questions and be given time to complete the first 2 questions for a dominant and recessive trait that they have. The next day students should be able to complete the rest of the assignment.
| 1. Students should first select a trait
from the one used in the Human Genetics project in which they have the recessive phenotype. |
| 2. Students (as a class, group or
individual) should hypothesize the phenotype of their parents (and
grandparents if possible) and explain
why. Making a flow chart to visualize this is recommended. |
| 3. Students then determine the phenotype of their parents
for homework. If possible, determine the
phenotype of grandparents as well. |
| 4. Students can then determine if
their hypothesis is correct and whether or not it fit their current
knowledge of genetics and trait dominance. |
| 5. Repeat steps 1-4 for a
trait in which the student exhibits the dominant phenotype. |
| Have students either
present their findings to the class or submit a report. They should
submit the pedigree analysis along with answers to the following question:
From the work you have done putting together your
pedigree, can you conclude for certain which trait is dominant?
Explain how you came to this conclusion. If you failed to make any
conclusion explain why you cannot make a conclusive statement.
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