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 Title: Role of Heterochromatic Knob DNA in Development and Flowering Time in Maize (Zea Mays L.) Author(s): Chughtai, Sajjad R. Department / Program: Genetics and Development Discipline: Genetics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Biology, Genetics Abstract: The present studies were undertaken to ascertain the genetic role of knob DNA in determining the rate of development and flowering time in maize (Zea mays L.). The knob compositions of 41 inbred lines and varieties of maize were determined. In almost all U.S. commercial lines, a large knob on the long arm of chromosome 7 was present, followed by one on the long arm of chromosome 4 and on the short arm of chromosome 9.Over 80 inbreds and varieties of maize were used for the genetic analyses. Extensive data on hybrids between knobless flints and various inbred lines convincingly demonstrated that the rate of development is determined by the knobless genotype, and not by the number of knobs. F$\sb2$ progenies from crosses between knobless genotypes and low-knob inbreds, and between related inbreds such as C103 and Mo17, exhibited a discontinuous pattern of inheritance. Data on 4L, 7L, 9S, and 2S knobs indicated that an allelic pair of knobs in homozygous condition (e.g., 7L/7L) delayed pollen shedding by three to four days, as compared to their knobless or heterozygous counterparts. A homozygous knob allows one or two more leaves to be initiated at the apex, and the position of the topmost ear to be moved up one or two nodes. Such a regulatory mechanism is not likely to reside in the knob DNA, the 180-bp tandem repeat, but in the genes that surround the knob, amounting to a cis-acting position effect or spreading effect. We propose the presence of a knob DNA binding protein that brings about a conformational change through condensation of the knob DNA, which spreads to neighboring genes.The role of knob DNA in adaptation of maize to its environment, and in combining ability in hybrids, are considered. The genomic, racial, and geographical distributions of chromosomal knobs are highly nonrandom, fitting an adaptive mode. With very few exceptions, the rate of development in maize is positively correlated with knob homozygosity. The greater the number of homozygous knobs, the longer the developmental period. Issue Date: 1988 Type: Text Description: 262 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988. URI: http://hdl.handle.net/2142/71759 Other Identifier(s): (UMI)AAI8823105 Date Available in IDEALS: 2014-12-16 Date Deposited: 1988
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