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Thinking Scientifically
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1. Why would Mendel’s observations have differed if the genes he studied were part of the same chromosome?

2. A white woman with fair skin, blond hair, and blue eyes and a black man with dark brown skin, hair, and eyes have fraternal twins. One twin has blond hair, brown eyes, and light skin, and the other has dark hair, brown eyes, and dark skin. What Mendelian principle does this real-life case illustrate?

3. Many plants have more than two sets of chromosomes. How would have four (rather than two) copies of a chromosome more effectively mask expression of a recessive allele?

4. In an attempt to breed winter barley that is resistant to barley mild mosaic virus, agricultural researchers cross a susceptible domesticated strain with a resistant wild strain. The F1 plants are all susceptible, but when the F1 plants are crossed with each other, some of the F2 individual are resistant. Is the viral resistance gene recessive or dominant? How do you know?


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Additional Questions and Terms

1. If you wanted to confirm Mendel’s law of independent assortment by recording the phenotypes and genotypes of the offspring of a dihybrid cross, what sort of strains would you choose to examine, and in what organism?

2. What are the three explanations for a trait that shows a great deal of variability in different individuals?

3. How can parents carry recessive lethal genes and not know it? Why is there no physical evidence for the existence of dominant lethal mutations?

4. A man and woman want to have children, but each is a known carrier of Tay-Sachs disease. To avoid the possibility that they will conceive a child who will inherit this untreatable, fatal disorder, the woman is artificially inseminated with sperm from a man who does not carry the Tay-Sachs gene. Why is this procedure a solution to the couple’s problem?

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