a

1
No Recombination
A
B
AB
AB
ab
ab
a
b
With Recombination
A
B
AB
Ab
aB
ab
a
b
2
Drosphila melangaster autosomal, recessive
traits ebony body (e)
spineless bristle (sp)
P0 wild type x ebony spineless /
/ x e/e sp/sp F1 wild type
(e/ sp/)

3
testcross e/ sp/ x e/e sp/sp

gamete gamete phenotype exp f
obs e sp e sp
ebony spineless 0.25 430 e sp
wild type 0.25 440
e sp e ebony 0.25 59
e sp sp spineless 0.25 71
4
Notation initial (null) hypothesis is that
genes are unlinked e/e sp/sp or e/
sp/ for genes known to be linked e sp/e
sp or e sp/ or e / sp
5
gamete gamete phenotype
obs 1 obs 2 e sp e sp
ebony spineless 430 59 e
sp wild type 440 71
e sp e ebony 59 430
e sp sp spineless 71 440
e sp
ebony, spineless x wild type
obs1 obs2

e
ebony x spineless
sp
6
Linkage analysis of multiple traits javelin
bristle, striped body, pink eyes 3-point test
cross jv/ str/ pi/ x jv/jv
str/str pi/pi
gametes gametes progeny phenotype progeny jv
str pi jv javelin 294 jv str pi
str pi striped, pink 287 jv str pi jv str
pi javelin, striped, pink 140 jv str pi
wild type 139 jv str pi pi pink
66 jv str pi jv str javelin, striped 65 jv
str pi jv pi javelin, pink 4 jv str pi
str striped 5
7
Take-home points spatial arrangement of
genes - gene interactions - genome evolution
transmission patterns of linked genes - most
offspring will inherit the allele combinations
present in their parents - recombination is
rare, detect numerically from testcross
progeny - parental allele combinations (on the
chromosome) - genetic distance between linked
loci - gene order (genetic map)