自殖世代における遺伝的固定と連鎖切断

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タイトル別名
  • Fixation of genes and breakup of linkage blocks in selfed generations.
  • 自殖世代における遺伝的固定と連鎖切断〔英文〕
  • ジショク セダイ ニ オケル イデンテキ コテイ ト レンクサリセツダン エイ

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Occurrence of meiotic crossover and transmission of recombined chromosomes in selfed generations after a cross of two pure lines were simulated by applying the Monte Carlo method and the changes in the magnitude of heterozygosity and in the length of parental linkage blocks with the generations were examined. The number of generations required for the fixation of all the genes on a chromosome was proportional to the logarithm of the number of crossovers per chromosome (NCR). Increase in NCR from 1 to 10 resulted in the delay of fixation generation from 4.25 to 7.32. A cumulative distribution curve with NCR=z for the frequency of chromosomes homozygous for the whole length was roughly equivalent to the curve for independent factors with the number of factors equal to z multiplied by 3.3 to 4.0. The number of generations needed for the fixation of the whole genome depended upon the number of pairs of homologous chromo-somes involved in the genome as well as NCR. When NCR=2, for instance, the generation when 95% or more of the individuals come to complete fixation is Fg for a single pair of chromosomes, while F12 and F18 for a set of 7 and 12 pairs, respectively. Delay of fixation generation with increase of NCR was similar irrespective of the number of chromosomes. The average number of breakups of the linkage blocks increased from 0.95 to 7.31 in proportion to the increase in NCR from 1 to 10 and the maximum number ranged from 5 to 17. For a particular value of NCR, there was a significant positive correlation between the number of generations needed for fixation and the number of breakups. When 1% of the individuals with the highest number of breakups was selected, the average number of breakups was 2 (NCR=1) to 5 (NCR=10) times that of the original, while the number of generations needed for fixation changed into F9 or so irrespective of NCR. Increase in NCR only in a single generation was effective in raising the number of breakups when the increase occurred in early generations. It was found moreover by simulation that the fixation of the whole genome in as early as F2 by applying the technique of anther culture and doubling of chromosome number resulted in a narrower distribution of the number of breakups and highly recombined genotypes could not be obtained.

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