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Genotypes, Phenotypes, and Karyotypes

The common fruit fly, Drosophila melanogaster, has been the subject of genetic study for over 100 years. In fruit flies, curly wings are dominant to straight wings.

1. How would you designate the genotype of a homozygous curly-winged fly? _________

2. How would you designate the genotype of a straight-winged fly? ___________

3. What is the phenotype of the heterozygous fly? ____________

4. What is the result of a cross of a heterozygous curly-winged fly to a straight-winged fly (include both genotype and phenotype with fractions of each)?

5. What is the result of a cross between two heterozygous flies (include both genotype and phenotype with fractions of each)?

6. I crossed two flies and I forgot to write down their phenotypes or genotype. If the ½ of the progeny have curly wings and ½ have straight wings, what are the genotypes and phenotypes of the two parents? (3 points)

7. Karyotyping assignment http://www.biology.arizona.edu/Human_Bio/activities/karyotyping/karyotyping.html.
Answer questions A1, A2, B1, B2, C1, and C2.

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Genetics Problems (20 points)

The common fruit fly, Drosophila melanogaster, has been the subject of genetic study for over 100 years. In fruit flies, curly wings are dominant to straight wings.

1. How would you designate the genotype of a homozygous curly-winged fly? _________

Curly wings are dominant, so we use a capital letter to represent the curly-winged allele. Let's call it C. Homozygous means that the fly has two identical alleles (in this case two copies of the C allele). The genotype of a homozygous curly-winged fly would be CC.

2. How would you designate the genotype of a straight-winged fly? ___________

Since we called the curly allele C, let's call the straight allele c (use a lower-case letter). Because the straight-winged allele is recessive, the only way for a fly to have straight wings is if it had two copies of the straight-winged allele (homozygous). The genotype of a straight-winged fly would be cc.

3. What is the phenotype ...

Solution Summary

This problem set has 6 questions about phenotypes and genotypes of fruit flies and their offspring.

The 7th question provides a website with questions on karyotyping and chromosomal abnormalities. This website has case studies of 3 people. For each person, you are asked how their karyotype (chromosomal arrangement) would be designated and what the most likely diagnosis would be.

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