Chromosomal interchanges in plants

Induced interchange heterozygosity in Sesbania aegyptiaca (Poir.) pers.

“…Symmetrical shape of chromosomes together with terminalized chiasmata, increase the probability of disjunctional orientation , because rings with equal intercentromeric distance and terminal chiasmata tend to be more pliable and can easily arrange disjunctionally (Burnham 1956, Darlington 1965. Furthermore alternate/disjunc tional orientation in ring multiples is greater if centromeres are effectively equidistant, so that each centromere is in equal communication with those adjacent to it and becomes co-orientated relative to both of them.…”

Cytogenetics of Thirteen Radiation-Induced Reciprocal Translocations in <i>Collinsia heterophylla</i>

“…Reciprocal translocations in a particular species show either random (approx imately equal frequency of meiocytes displaying alternate or adjacent configura tions) or directed (significantly more than 50% meiocytes showing alternate con figuration) orientation of the interchange complexes at metaphase I but not both (Burnham 1956). Furthermore, species which show directed orientation of the interchange complexes possess certain cytogenetic features , namely: i) the chro mosomes are relatively uniform in length, ii) the centromeres are more or less median in position, and iii) the chiasmata are localized towards the ends (terminal or sub-terminal chiasmata) (Burnham, 1962).…”

Genic heterozygosity maintained by chromosomal interchanges in rye

“…In the case of interchanges, unbalanced gametes -can arise in an adjacent orientation of multivalents at Metaphase I. Various hypotheses have been proposed to explain the existence and maintenance of structural heterozygosity for interchanges that occur in many natural populations, especially in plants (Burnham, 1956). On the basis of the totally or partially suppressed crossing-over in interstitial segments (Burnham, 1962) it has been suggested that structural heterozygosity could be advantageous since it could serve as a mechanism for the possible establishment of coadapted gene complexes within the interstitial segments, and/or for preserving the genie heterozygosity in translocation heterozygotes through sucessive generations.…”