1. Exploration Lab
Karyotyping

2. Analysis
1. Examining Data: Examine your karyotype. Is the fetus male or female? How do you know?
The sex is determined by examining the sex chromosomes.
XX = female
XY = male

3. Analysis
2. Examining Data: Will the baby have Down syndrome? How do you know?
If the autosomes are all paired and there are no extras, the karyotype is normal. The baby will not have Down syndrome.
If there is a third chromosome 21, then the baby will have Down syndrome.

4. Analysis
3. Explaining Events: The Y chromosome closely resembles many of the other chromosomes. What did you have to do to determine that it was the Y chromosome?
The length of the chromosome and position of the centromere were measured. Banding patterns were compared, and it was determined that there was only one chromosome present and not a pair. This helped to distinguish the Y chromosome from others of similar size and shape.

5. Analysis
4. Recognizing Patterns: If the karyotype you constructed was for a female with Down syndrome, what chromosome changes would be evident?
There would be two X chromosomes indicating a female, and an extra 21st chromosome indicating trisomy 21, or Down syndrome. The total chromosome number would increase to 47.

6. Analysis
5. Identifying Relationships: A pedigree is a diagram that shows the presence or absence of a trait in each person in each generation. How does a karyotype differ from a pedigree?
A karyotype provides information about a single individual, and does not show several generations. A karyotype is a diagram of an individual’s chromosomes that can show chromosomal mutations. A pedigree traces a trait or point mutation over several generations.

7. Conclusions
1. Interpreting Information: If your job were to inform the parents of the fetus of their test results, what would you say?
Answers will vary. Students should cite evidence to support their conclusions that the fetus is male or female, and does or does not have Down syndrome or other chromosomal abnormality. Other conditions may exist that cannot be determined by karyotype.

8. Conclusions
2. Drawing Conclusions: Why are karyotypes important tools for geneticists?
Karyotypes supply important, specific information related to certain genetic chromosomal problems and the sex of an individual.

9. Conclusions
3. Evaluating Models: Can the analysis of a karyotype reveal point mutations? Explain your answer.
No. Karyotypes can only reveal certain chromosomal mutations. Point mutations involve base pairs in the DNA, and these cannot be seen in a karyotype.

10. Conclusions
4. Applying Conclusions: You have prepared a karyotype of an individual and have found that one of the chromatids of chromosome 4 is shorter than its homologue. What can you conclude has happened to this chromosome?
Chromosome 4 has undergone a deletion in which part of the chromosome has been lost. Too much missing information can be a fatal situation for the fetus.