UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1468 
Washington, D. C. 
March, 1927 
VARIABILITY IN THE LINKAGE OF TWO SEED CHARACTERS OF MAIZE 
By G. N. Collins, Senior Botanist in Charge, and J. H. Kempton, Associate 
Botanist, Biophysical Laboratory, Bureau of Plant Industry 
CONTENTS. 
Page 
Introduction 1 
Statistical treatment 4 
Variability of crossover rate 8 
Variability not unique in C— Wx 
linkage nor in Chinese-Algeria 
maize hybrids 8 
Crossover rate more variable in 
some progenies than in 
olthers 10 
Variability of crossing over no 
greater in male than in fe- 
male gametes 13 
Variability of crossing over no 
greater in upper than in lower 
ears 15 
Variability of crossing over no 
greater in the base than in 
the tip of the ear 15 
Crossing over generally less va- 
riable in several samples of 
the same individual than in 
single samples from several 
individuals 16 
Crossing over less variable in 
samples from different parts 
of the same male inflores- 
cence than in samples from 
several inflorescences 18 
Variability of crossing over no 
greater in old than in fresh 
pollen 19 
Crossing over no more variable 
in first than in last gametes 
formed 19 
Crossover ratio more variable 
than Mendelian ratios 20 
Variability in the crossover class 
not the result of differential 
death rate of zygotes 21 
Page 
Variability of crossover rate — Contd. 
Variability of rate of crossing 
over alike in plants heterozy- 
gous and homozygous domi- 
nant for R 23 
Rate of crossing over between the 
C-Wx genes 24 
Crossing over greater in some 
progenies than in others 25 
Proportion of crossover to non- 
crossover gametes not af- 
fected by vitality of pollen 27 
Crossing over reduced by the 
R aleurone factor in a heter- 
ozygous condition 31 
Rate of crossing over between 
C and Wx associated with 
the Su factor 35 
Rate of crossing over differs in 
the two sexes 36 
Rate of crossing over not alike 
in the upper and lower ears 
of the same plant 45 
Rate of crossing over not alike 
in base and tip of the same 
ear 49 
Length of silk not a factor in 
rate of crossing over 52 
Variations in meteorological 
conditions during anthesis 
not a factor in rate of cross- 
ing over 53 
Rate of crossing over similar in 
first and last pollen shed 55 
Correlations 56 
Discussion 60 
Summary 62 
Literature cited 64 
INTRODUCTION 
The improvement of plants and animals by systems of breeding 
is contingent upon the inheritance of the qualities it is desired to 
perpetuate. In consequence, much emphasis of late has been placed 
upon an understanding of the fundamental principles underlying 
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