Genetic Linkage

Creating a Linkage Hypothesis

• Morgan used Drosophila as an experimental organism to prove linkage
• Crossed red eye, normal wing (pr+pr+ vg+vg+) and purple eye vestigal wing (prpr vgvg)
• The F1 flies were test crossed
• Observed deviation from the 1:1:1:1 ratio

F1 Gamete	Testcross Distribution	Gamete Type
pr+ vg+	157	Recombinant
pr+ vg	965	Parental
pr vg+	1067	Parental
pr vg	146	Recombinant

Coupling Cross Chi-Square Test

F1 Gamete	Observed	Expected	(O-E)2/E
pr+ vg+	1339	709.75	557.9
pr+ vg	151	709.75	439.9
pr vg+	154	709.75	435.2
pr vg	1195	709.75	331.8
Total	2839	2839	X2=1764.8