Estimating Distances Between Genes
Estimating Linkage From Three-Point Crosses
Recombination Involves Exchange Of Chromosomal Material
Study Questions
Study Questions
1. When analyzing a segregation ratio of phenotypes in one populaton, what result suggests that two genes are linked on the same chromosome?2. Two genes can be coupling or repulsion phase on a parental chromosome. What is the difference between the two?
3. In Drosophila, b+ is the allele for normal body color and at the same gene b is the allele for black body color. A second gene controls wing shape. The shape can be either normal (vg+) or vestigial (vg). A cross is made between a homozygous wild type fly and fly with black body and vestigial wings. The offspring were then mated to black body, vesitigial winged flies. The following segregtion ratio was observed:
| Phenotype | # Observed |
|---|---|
| Wild Type | 405 |
| Normal, vestigial | 85 |
| Black, normal | 100 |
| Black, vestigial | 410 |
Are these two genes linked? How did you come to this conclusion? What calculation would you perform to confirm you conclusion?
4. What is the relationship between recombination frequency and genetic distance?
5. How do you recognize double cross progeny when analyzing the segregation data of three genes in a population?
6. Describe the experiment of Creighton and McClintock that demonstrated that recombination invovled a physical exchange of chromosomal material?
7. How is linkage determined in humans? What information and assumptions are used in calculating linkage in humans.?
Copyright © 1997. Phillip McClean