Repeated and non-repeated nucleotide sequences in diploid and polyploid wheat species

Abstract

Reassociation rate studies of dissociated DNAs from diploid, tetraploid and hexaploid wheat species revealed that all the species have a large proportion of their DNA which shows characteristics of repeated DNA, under the conditions used in the reassociation experiments (fragment size about 450 nucleotide pairs, incubation at 60°C. in 0.12 M phosphate buffer, C₀t=100). The relative proportion of this fraction increased with ploidy in tetraploid and hexaploid wheat. Genome size (amount of non-repeated DNA) was larger in hexaploid and tetraploid wheat in comparison with diploid wheat. Heterologous reassociation of repeated and non-repeated fractions of DNAs showed considerably more divergence in the repeated sequences at both diploid and at polyploid levels. Non-repeated sequences of wheat species showed greater homologies, and appear to be more conservative in composition.