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Seed Production And Gene Diversity
Genetic diversity is often a major consideration in e g forest crops. Group coancestry of a population Consider the gene pool of a seed orchard crop or other source of seeds with parents. The gene pool is large as there are many seeds in a seed crop, so there is no genetic drift. The probability that the first gene originates from genotype i in the seed orchard is pi, and the probability that the second originates from genotype j is pj. The probability that these two genes originate from the orchard genotypes i and j are identical by descent (IBD) is θij. This is the Malecot's method of coancestry Malecot's coancestry coefficient, f, refers to an indirect measure of genetic similarity of two individuals which was initially devised by the French mathematician Gustave Malécot. f is defined as the probability that any two alleles, sampled ... (or "coefficient of kinship"; "coefficient of relationship" is a similar measure which can be computed) between genotype i and j. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is distinguished from ''genetic variability'', which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will possess variations of alleles that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele. The population will continue for more generations because of the success of these individuals. The academic field of population genetics includes several hypotheses and theories regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seed Orchard
A seed orchard is an intensively-managed plantation of specifically arranged trees for the mass production of genetically improved seeds to create plants, or seeds for the establishment of new forests. General Seed orchards are a common method of mass-multiplication for transferring genetically improved material from breeding populations to production populations (forests) and in this sense are often referred to as "multiplication" populations. A seed orchard is often composed of grafts (vegetative copies) of selected genotypes, but seedling seed orchards also occur mainly to combine orchard with progeny testing. Seed orchards are the strong link between breeding programs and plantation establishment. They are designed and managed to produce seeds of superior genetic quality compared to those obtained from seed production areas, seed stands, or unimproved stands. Material and connection with breeding population In first generation seed orchards, the parents usually are phenotypical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Drift
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. It can also cause initially rare alleles to become much more frequent and even fixed. When few copies of an allele exist, the effect of genetic drift is more notable, and when many copies exist, the effect is less notable. In the middle of the 20th century, vigorous debates occurred over the relative importance of natural selection versus neutral processes, including genetic drift. Ronald Fisher, who explained natural selection using Mendelian genetics, held the view that genetic drift plays at most a minor role in evolution, and this remained the dominant view for several decades. In 1968, population geneticist Motoo Kimura rekindled the debate with his neutral theory of molecular evolution, which claims that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malecot's Method Of Coancestry
Malecot's coancestry coefficient, f, refers to an indirect measure of genetic similarity of two individuals which was initially devised by the French mathematician Gustave Malécot. f is defined as the probability that any two alleles, sampled at random (one from each individual), are identical copies of an ancestral allele. In species with well-known lineages (such as domesticated crops), f can be calculated by examining detailed pedigree records. Modernly, f can be estimated using genetic marker data. Evolution of inbreeding coefficient in finite size populations In a finite size population, after some generations, all individuals will have a common ancestor : f \rightarrow 1 . Consider a non-sexual population of fixed size N, and call f_i the inbreeding coefficient of generation i. Here, f means the probability that two individuals picked at random will have a common ancestor. At each generation, each individual produces a large number k \gg 1 of descendants, from the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classical Genetics
Classical genetics is the branch of genetics based solely on visible results of reproductive acts. It is the oldest discipline in the field of genetics, going back to the experiments on Mendelian inheritance by Gregor Mendel who made it possible to identify the basic mechanisms of heredity. Subsequently, these mechanisms have been studied and explained at the molecular level. Classical genetics consists of the techniques and methodologies of genetics that were in use before the advent of molecular biology. A key discovery of classical genetics in eukaryotes was genetic linkage. The observation that some genes do not segregate independently at meiosis broke the laws of Mendelian inheritance and provided science with a way to map characteristics to a location on the chromosomes. Linkage maps are still used today, especially in breeding for plant improvement. After the discovery of the genetic code and such tools of cloning as restriction enzymes, the avenues of investigation open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
