Linkage and Distored Mendelian Ratios

Estimating Distances Between Genes

Estimating Linkage From Three-Point Crosses

Recombination Involves Exchange Of Chromosomal Material

Measuring Linkage in Humans

Lod Score Method

Study Questions

Genetic Linkage Overheads

Genetic Linkage WWW Links

Genetic Topics

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