Browsing by Author "De Ramos, Mariano Bauyon"

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    The evolution of a sex-linked genetic factor
    De Ramos, Mariano Bauyon (Virginia Tech, 1961-08-15)
    The genetical theory of evolution is best understood by a knowledge of the distribution of gene frequencies. The sequence of changes in genes, primarily due to effects of mutation, selection, migration, and many other environmental influences, would also gradually change gene frequencies after a long period of time. The distribution of gene frequencies is determined by application of theories of probability and mathematics. In particular, Wright's diffusion theory (14) and early works of Fisher (6,7) and Kolmegorov (9) play a central role. The aim of this thesis is to discover the evolutionary significance of mutation, selection, and random mating in the case of sex-linked factors when the generation structure of the population is overlapping. To facilitate the application of mathematical theory, we assume the population size at any time is large and constant denoted by N. Instead of discussing the individual genotype frequencies, we introduce a properly defined random variable U, approximately the proportion of "a" genes in the population. The first and second moments of the change in U during the birth-death event are obtained. For the diffusion process to work out, we let the time be a function of N, and by moment generating functions the diffusion equation (or Fokker-Planck equation) is justified when N tends to infinity. Following methods of solution given by Barucha-Reid (2), Kimura (8), Li (10), Moran (11,12), Watterson (13), and Wright (14), the density function for the "a" gene frequency is obtained.
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    The growth pattern of various body and carcass parts and proportions of beef steers as influenced by different planes of nutrition
    De Ramos, Mariano Bauyon (Virginia Tech, 1968-12-15)
    Ten attributes representing various body and. carcass measurements of beef steers were considered for statistical analysis. The slaughter data were obtained from an experiment conducted at Blacksburg, Virginia, by members of the Animal Science Department of the Virginia Polytechnic Institute, described by Kelly et al. (1968). The objective of the study was to obtain estimates of the effects of slaughter time (age), and of the energy level of the ration fed, on the body proportions and carcass composition of beef steers from approximately 7 to 30 months of age. The nutritional regimens used were: Ration I - maintenance; Ration II - full feed of hay; Ration III - limited concentrate plus full feed of hay; Ration IV - full feed of a fattening ration. According to the design of the experiment, the linear model included the general mean, the effects of slaughter time, breed, trial, slaughter time by trial interaction and slaughter time by breed interaction, and an error term. The first part of the investigation dealt with the analysis of variance of the percentage hot carcass to determine whether the effects of breed and trial were significant. In the second part, only the general mean, the slaughter time effect, and an error term were included in the model. When the slaughter time was found significant or highly significant, the sum of squares due to slaughter time was divided into regression components to determine which polynomial regression model best described the relationship between the body component mean and age. The results of the statistical analyses were as follows: 1. Breed and trial effects on the percentage hot carcass were insignificant in all but ration II, in which trial was significant. 2. Slaughter time by trial interaction effect was significant in all rations; slaughter time by breed was not. 3. The percentage hot carcass behaved in a parabolic manner with age, which was concave upward at lower planes of nutrition; the pattern changed to cubic at higher planes. 4. Age had no effect on the mean empty-body weight with steers on ration I; the effect was linear on ration II; quadratic on rations III and IV. Similar growth pattern was obtained for the percentage meat. 5. The percentage of front quarter to total carcass increased proportionately with age in all rations; the opposite trend was obtained for the percentage hind quarter. 6. The relationship of weight of the head, expressed as percentage of the live weight, with respect to age or slaughter time was linear with positive slope on rations I and II and negative on rations III and IV. 7. The percentage moisture in the meat showed a quartic regression with age on ration I presumably due to random fluctuation of the means. For rations II and III, the relationship was quadratic and concave downward; for ration IV, it was linear with negative slope. 8. The percentage crude protein and the percentage ash behaved similar to that of the percentage head, while opposite pattern was obtained for the ether extract.