8. Segregation in autotetraploid maize. To deterwine the nature of segregation of some genes in autotetraploid maize, backcrosses were made involving the genes B(plant color booster) and Su(sugary endosperm).

Cross B b No. of Plants Ratio
BBbb x bbbb 437 135 572 3.25 : 1

Some difficulty was encountered in classifying the progeny of the backcross, sun red (BBbb) x green (bbbb), since there was a great deal of variation in degree of coloration. Some plants were distinctly sun red, others resembled dilute sun red, while still others showed a tinge of color on and around the ligules. Undoubtedly errors were made in classification, there being an excess of green plants. However, the backcross ratio approaches 3.67 : 1. Since the type of segregation is a function of cross over distance between the gene locus and the spindle fiber attachment region, this would indicate that the gene B is located fifty or more units from the spindle fiber attachment region and that chromatid segregation had occurred.

Cross Su su No. of plants Ratio
Su Su su su x
su su su su
2877 645 3522 4.46 : 1
su su su su x
Su Su su su
369 87 456 4.24 : 1
  3246 732 3978 4.43 : 1

There was no difficulty in classifying sugary segregates in a backcross of autotetraploids. The ratio of 4.43 Su : 1 su indicates that this gene has segregated on a basis intermediate between the random distribution of four chromosomes and random distribution of eight chromatids, and suggests that the gene Su is located about 20 cross over units from the spindle fiber attachment region.

H. E. Fischer