Release of Genetic Variability Through Recombination. I. Drosophila Pseudoobscura

Abstract

ENDEL discovered that genes segregate, rather than blend during the process 1 This research was sponsored by the Office of Naval Research under Contract Number Nonr-2 The work reported in this article has been carried out under Contract Number AT-(30-1)-

The Estimation of Relative Fitness of Drosophila Populations. II. Experimental Evaluation of Factors Affecting Fitness

“…A new population has been formed from two previously separated ones, and this population will have its own fitness value. Thus we can estimate the relative fitnesses of two populations and find, for example, that the relative fitness of population A is higher than that of population B, but this does not allow the prediction of the relative fitness of the new population formed from (A+ B) (see also Vetukhiv, 1953Vetukhiv, , 1954Wallace, King, Madden, Kaufmann, and McGunnigle, 1953;Brncic, 1954;Cordeiro and Dobzhansky, 1954;Spassky et al, 1958;Dobzhansky et al, 1959;and Spiess, 1959).…”

Chromosomal Polymorphism in Drosophila Paramelanica Patterson

“…In these cases the cost of maintenance of such associations is the elimination of individuals carrying nonadaptive chromosomes produced by recombination. Associations of this sort have been demonstrated in D. melanogaster (MISRO 1949;WALLACE et al 1953), in D. pseudoobscura (DOBZHANSKY 1946SPASSKY et al 1958), in D. prosaltans (DOBZHANSKY et al 1959) and in D. persimilis (SPIESS 1959).…”

“…In such species it might be expected that systems capable of producing lethal or semilethal recombinant chromosomes would not occur on the X chromosome. As stated by SPASSKY et al (1958), "-one third of the X chromosomes in a population are carried in males which would die if they had a sex-linked lethal. Therefore, X chromosomes capable of giving sex-linked lethals by recombination with other X's in the same population would be discriminated against by natural selection.…”

Release of Genetic Variability Through Recombination. Ii. Drosophila Persimilis

“…The plan of the experiments is the same as that described in the preceding paper ( SPASSKY et al 1958), namely, second chromosomes which produced "normal" or subvital effects on viability were chosen from samples of flies taken from two different localities, ten chromosomes from each locality. A total of 45 intralocality crosses from each locality and 100 interlocality crosses were made.…”

“…Nonadditive effects (interactions) are all significant in persimilis, on the other hand, and are of about the same magnitude as in pseudoobscura. SPASSKY et al (1958) point out that even though additive effects are significant for pseudoobscura (that is, that "good chromosomes give good recombination products"), correlations between values for chromosomes under control, intraand interconditions show little significance except that "chromosomes which give good recombination products in intrapopulational crosses tend to do so in interpopulational crosses also." From Table 7 it can be seen that these correlations in persimilis are not significant (with the possible exception of the SF original-SF intercross correlation) a fact which underlines the unpredictability of the recombinational effect.…”