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Thinking Scientifically
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1. Why doesn’t the inheritance pattern of linked genes disprove Mendel’s laws?

2. A normal-sighted woman with a normal-sighted mother and a color blind father marries a color blind man. What are the chances that their son will be color blind? their daughter?

3. A fetus dies in the uterus. Several of its cells are examined for chromosomal content. Approximately 75% of the cells are diploid, and 25% are tetraploid. What has happened, and when in development did it probably occur?

4. Why are there no male calico cats?

5. A fetus has an inverted chromosome. What information might reveal whether the expected child will have health problems stemming from the inversion?

6. Patricia Jacobs concluded in her 1965 Nature article on XYY syndrome, “It is not yet clear whether the increased frequency of XYY males found in this institution is related to aggressive behavior or to their mental deficiency or to a combination of these factors.” Why is this wording unscientific? What harm could it (or did it) do?


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Additional Questions and Terms

1. In a new technology called sperm typing, researchers determine recombination frequencies between gene pairs in sperm cells, using DNA probes to detect specific alleles.

  • a. What information would researchers need to know to determine whether a certain allele configuration in sperm is parental or recombinant?
  • b. What are two advantages of working with sperm to determine recombination frequencies?
  • 2. The tribble is a cute, furry creature ideal for embryonic experimentation. Cells from tribble embryos genetically destined to become brightly colored adults can be transplanted into tribble embryos that would otherwise develop into albino (pure white) adults. Investigators can follow the numbers and positions of cells descended from the original transplants by observing the pattern of colored patches in the adult tribble. A gene in the tribble confers coat color. The brown allele B is dominant to the orange allele b. A single cell from a Bb female embryo at the 8-celled state is transplanted into an albino embryo. The resulting adult tribble has both brown and orange patches on an albino background. But when a single cell from a Bb embryo at the 64-celled stage is transplanted into an albino embryo, only orange patches, or only brown patches, appear in the adult.

  • a. State the genetic principle demonstrated.
  • b. What is the difference between the two experiments?
  • 3. Which chromosomal anomaly might you expect to find more frequently among the members of the National Basketball Association than in the general population? Cite a reason for your answer.

    4. For an exercise in a college genetics laboratory course, a healthy student takes a drop of her blood, separates out the white cells, stains her chromosomes, and constructs her own chromosome chart. She finds only one chromosome 3 and one chromosome 21, plus two unusual chromosomes that do not seem to have matching partners.

  • a. What type of chromosomal abnormality does she have?
  • b. Why doesn’t she have any symptoms?
  • c. Would you expect any of her relatives to have any particular medical problems? If so, which ones?
  • 5. Stella Walsh won a gold medal in the 100-meter dash in the 1932 Olympics. In 1980, she was killed in a robbery. An autopsy revealed ambiguous genitalia and her karyotype was XY. Another supposedly female athlete, Ewa Klobukowska, who won a 1965 world record for the 100-meter dash, was also found to be XY. What was probably unusual about their Y-chromosomes?

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