Biomedical subjects

J Doebley

Publications and source records attributed to J Doebley.

24 records · Page 2Linked to original sources

PubMed1992

Mapping the genes that made maize.

George Beadle proposed that the striking morphological differences between cultivated maize and its probable wild progenitor (teosinte) were initiated by a small number of mutations with large effects on adult morphology. Recent genetic analyses using molecular markers provide some support for this view and show where in the maize genome the putative loci are likely to be located. This work sets the stage for fine-scale linkage mapping of these genomic regions and the eventual cloning of the genes involved in this remarkable evolutionary transformation.

Chromosome Mapping↗

PubMed1992

Comparative genome mapping of Sorghum and maize.

Linkage relationships were determined among 85 maize low copy number nuclear DNA probes and seven isozyme loci in an F2 population derived from a cross of Sorghum bicolor ssp. bicolor x S. bicolor ssp. arundinaceum. Thirteen linkage groups were defined, three more than the 10 chromosomes of sorghum. Use of maize DNA probes to produce the sorghum linkage map allowed us to make several inferences concerning processes involved in the evolutionary divergence of the maize and sorghum genomes. The results show that many linkage groups are conserved between these two genomes and that the amount of recombination in these conserved linkage groups is roughly equivalent in maize and sorghum. Estimates of the proportions of duplicated loci suggest that a larger proportion of the loci are duplicated in the maize genome than in the sorghum genome. This result concurs with a prior estimate that the nuclear DNA content of maize is three to four times greater than that of sorghum. The pattern of conserved linkages between maize and sorghum is such that most sorghum linkage groups are composed of loci that map to two maize chromosomes. This pattern is consistent with the hypothesized ancient polyploid origin of maize and sorghum. There are nine cases in which locus order within shared linkage groups is inverted in sorghum relative to maize. These may have arisen from either inversions or intrachromosomal translocations. We found no evidence for large interchromosomal translocations. Overall, the data suggest that the primary processes involved in divergence of the maize and sorghum genomes were duplications (either by polyploidy or segmental duplication) and inversions or intrachromosomal translocations.

Chromosome Mapping↗

PubMed1991

Genetic analysis of the morphological differences between maize and teosinte.

Molecular marker loci were used to investigate the inheritance of morphological traits that distinguish maize (Zea mays ssp. mays) from a closely related wild relative, teosinte (Z. mays ssp. mexicana). Regression and interval mapping analyses gave largely congruent results concerning the numbers of loci controlling the morphological traits and the magnitudes of their effects; however, interval mapping tended to give larger estimates for the magnitudes of the effects of the morphological trait loci. This tendency was exaggerated for traits that were non-normally distributed. Variation for most inflorescence traits is controlled by one or two regions of the genome with large effects plus several other regions with relatively small effects. As such, the data are congruent with a mode of inheritance for most traits involving one or two major loci plus several minor loci. Regions of the genome with large effects on one trait consistently had smaller effects on several other traits, possibly as a result of pleiotropy. Most of the variation for the dramatic differences in inflorescence morphology between maize and teosinte is explained by five restricted regions of the genome. One of these regions encompasses a previously described gene, tb1 (teosinte branched), and the effects of this region on inflorescence architecture are similar to the known effects of tb1. Implications of this work for the genetic basis of morphological evolution in plants are discussed.

Biological Evolution↗

PubMed1990

Genetic and morphological analysis of a maize-teosinte F2 population: implications for the origin of maize.

Genes controlling the dramatic morphological differences between maize and its presumed progenitor (teosinte) were investigated in a maize-teosinte F2 population through the use of molecular markers. Results indicate that the key traits differentiating maize and teosinte are each under multigenic control, although for some traits, such as the number of ranks of cupules, the data are consistent with a mode of inheritance that would involve a single major locus plus several modifiers. For other traits, such as the presence/absence of the pedicellate spikelet, the data indicate multigenic inheritance with no single locus having a dramatically larger effect than the others. Results also indicate that the tunicate locus (Tu) had no major role in the origin of maize, despite previous opinion that it was involved. The major loci affecting the morphological differences between maize and teosinte are located on the first four chromosomes. The data suggest that the differences between teosinte and maize involve, in part, developmental modifications that enable (i) primary lateral inflorescences, which are programmed to develop into tassels (male) in teosinte, to become ears (female) in maize, and (ii) the expression of male secondary sex traits on a female background in maize. Similar changes were likely involved in the origin of maize.

Journal Article↗

PubMed1986

A gene modifying mitochondrial malate dehydrogenase isozymes in Sorghum (Gramineae).

Malate dehydrogenase (MDH) isozymes extracted from dark-grown seedlings of Sorghum species are encoded by at least two genes with their products localized in the mitochondria (mt) and one gene with its products localized in the cytosol. In homozygous genotypes, the three mt-MDH isozymes represent two homodimers and an intergenic heterodimer. For some plants of S. virgatum and S. aethiopicum, the three mt-MDH isozymes migrate about 3 mm faster (more anodally) when electrophoresed on starch gels. The F1's of plants with normal and fast mt-MDHs had normal migration; the F2's segregate 3:1 for normal to fast migration. It is suggested that a single gene, Mmm (mt-MDH modifier), controls this modification of normal migration and that fast migration occurs when the recessive allele (mmm-m) is homozygous. The designation, Mmm, is borrowed from Zea mays, in which a similar gene has been described.

Electrophoresis, Starch Gel↗

PubMed1986

Nucleotide sequence of the split tRNAleu(UAA) gene from Sorghum bicolor chloroplasts.

The nucleotide (nt) sequence of the split tRNAleu(UAA) gene and 328 nt of its flanking regions from sorghum chloroplasts (cp) has been determined. This gene is located in the BamHI-6 fragment in a map position very similar to that of maize. The exon of sorghum tRNAleu gene has an identical nt sequence to its counterpart in maize. Although the 450 nt of intron in sorghum is 8 nt shorter than that of maize, the nt sequence between them shows 97% homology. Like maize and broad bean, the intron from sorghum cp tRNAleu gene could be folded into a secondary structure which is similar to the postulated structure of the intron from the auto-spliceable rRNA precursor of Tetrahymena. Both introns from sorghum and maize contain open reading frames (ORFs) which are conserved at the N terminus. The putative AUG initiation codon for both ORFs is located in the stem region of a 12-bp secondary structure of highly A + T-rich sequences.

Base Sequence↗