In Pursuit of the Gene

NOTES TO PAGES 222–224 © 335
vermillion (“v”) and forked (“f”) on a female X chromosome, one would never see
vermillion-eyed sons with forked bristles, as is illustrated in the diagram below.
P 1
F 1
w e
*
v f
v f
we we v f
+ +
*
New lethal
mutation
+
+ + +
w v f
e w v f
e
X
w v f *
Dies
e
7. Each of fifteen students performed ten crosses, and each of the crosses was
carried through three generations. The first generation was a control cross, used to
weed out any preexisting X-linked lethals in the mother. Once it was determined
that the grandmother did not contain any lethals, two further generations were
bred, mother and daughter. In this process four individual X chromosomes (two
from the mother, and two from the granddaughter) were tested for the presence of
newly created lethal mutations. Thus four X’s were examined per mating, and each
of fifteen students performed ten matings, so 600 X chromosomes were examined
in total (H. J. Muller, “The Measurement of Gene Mutation Rate in Drosophila, Its
High Variability, and Its Dependence upon Temperature,” Genetics 13 [1928]: 306).
8. H. J. Muller, “The Problem of Genic Modification,” paper read at the Fifth
International Genetics Congress, Berlin, and published in Verhandlungen des V.
Internationalen Kongresses für Vererbungswissenschaft: Supplementband I der Zeitschrift für inductive
Abstammungs- und Vererbungslehre (1928): 235.
9. Muller, “Mutation Rate in Drosophila,” 311–312.
10. H. J. Muller and Edgar Altenburg, “The Rate of Change of Hereditary Factors
in Drosophila,” Proceedings of the Society for Experimental Biology and Medicine 17 (1919): 12.
11. H. J. Muller to Edgar Altenburg, Sept. 10, 1919, Muller MSS.
12. Muller, “Genic Modification,” 235.
13. Ibid., 318.
X
Mapping lethals.
Illustration by Tamara L. Clark.
+ + +