Maize Genetics Cooperation Newsletter vol 81 2007
In last year�s MNL (80:31), we reported that three mutable and two stable r1 haplotype-specific aleurone color enhancers map to the same location on chromosome 2 and are likely allelic. We tested the mutable factors Fcu with arv‑m594, arv‑m594 with arv‑m694, and Fcu with arv‑m694. We also tested the stable full color enhancer Arv‑V628#16038 with a full color Fcu revertant, Fcu‑R2003‑2653‑6. However, direct linkage tests had not been performed between the mutable factors and the stable factors. We report the results of such tests in this article. We tested linkage of the mutable factor arv-m594 with the stable factor Arv‑V628#16038, and the linkage of the mutable factor Fcu with the stable Fcu revertants Fcu‑R2003‑2653‑2 and Fcu‑R2003‑2653‑6.
All tests were conducted as follows: Lines homozygous for the two factors, and homozygous for either r1‑g, or for a responsive r1 haplotype, were crossed together. The resulting F1�s were outcrossed as males to the responsive r1 haplotype R1‑r(Venezuela559‑PI302355) without any factors present. The parental classes would be expected to have either mutable or full colored aleurones, the double factor recombinant class would be expected to have full colored aleurones, and the recombinant class lacking both factors would be expected to have stable pale aleurones. Kernels from these crosses were classified as mutable, colored, or pale/colorless. The exceptional pale or colorless kernels were planted last summer and the resulting plants self-pollinated and outcrossed to R1‑r(Venezuela559‑PI302355) in order to test the genotypes of these kernels. Since the only recombinant class that can be detected by these experiments is the class lacking both factors, we doubled the number of recombinants in this class in order to account for the double mutant class for the purpose of calculating linkage values. The results are presented below:
arv‑m594 with Arv-V628#16038. From the linkage cross, we isolated 29 pale and 8 colorless kernels from a population of 7,475 kernels. Upon further testing of the pale and colorless exceptions, 6 proved to carry Arv‑V628#16038 and 21 carried arv‑m594 and were thus members of parental classes and not recombinants. Ten kernels did not germinate and were not tested. Based on our failure to recover recombinants from among the high proportion of exceptions tested, we calculate that the linkage between these two factors is less than 0.03 � 0.02 cM. Thus, we conclude that these two factors are very tightly linked and most likely allelic.
Fcu with Fcu‑R2003‑2653‑2. We isolated one colorless kernel from a population of 3,936 kernels in this test. Upon further testing, this kernel proved to carry Fcu‑R2003‑2653‑2 and was not a recombinant. We calculate that the map distance between these two factors is less than 0.05 � 0.04 cM.
Fcu with Fcu‑R2003‑2653‑6. We isolated two pale and three colorless kernels from a population of 2,040 kernels in this test. Upon further testing, two kernels proved to carry Fcu‑R2003‑2653‑6 and two carried Fcu; one kernel failed to germinate and was not tested. Based on our failure to recover recombinants from among the exceptions tested, we calculate that the linkage between these two factors is less than 0.10 � 0.07 cM.
While we had strong reason to believe, based on indirect evidence, that the mutable enhancers map to the same location as these stable enhancers, these tests provide direct evidence for this. The two Fcu revertants we examined mapped to the same location as Fcu, as expected. We report elsewhere in this MNL the identification of two enhancers that map to linked sites. We plan to test these and other enhancers isolated from the Brink r1 haplotype collection for linkage in order to place them into linkage or �complementation� groups and identify the number of enhancer loci segregating in these lines.
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