Variations in repetitive DNA and evolution in reptiles

1. 1. Repetitive DNA evolution has been studied in various reptilian species by means of the reassociation kinetics technique. 2. 2. Quantitative variations in genome sizes depend on differences essentially in repetitive DNA, but also in single-copy DNA. 3. 3. The behaviour of the variations in repetitive DNA in relation to the various taxonomic relationships existing among the species assayed, leads us to think that the duplicated fractions are mostly free to evolve. 4. 4. Some difference in repetitive DNA evolution is observed in Chelonia on one side and in Squamata on the other. © 1981

Cyclic variation of chiasma frequency and distribution in Podarcis sicula (Reptilia: Lacertidae)

The seasonal variations of chiasma frequency and distribution have been studied in the lizard: Podareis sicula. In this species, as in Phyllodactylus (King & Hayman, Chromosoma 69: 131–154, 1978), chiasma frequencies vary following a definite annual cycle, and clearly different trends are shown by interstitial and terminal chiasmata. A comparison between these seasonal chiasma frequency variations and those of environmental temperature shows the existence of a clear correlation between these two parameters. However, this correlation is different in the two types of chiasmata, and may be different within the same type of chiasma depending on the period of the year. A more significant correlation is observed between chiasma cycles and annual variations of the haematic levels of sexual steroid hormones. In particular we observe a highly significant correlation between interstitial chiasma frequencies and testosterone concentration. A less precise correlation between terminal chiasma frequencies and estradiol concentration is also observed. In Podarcis, as in Phyllodactylus, the sperm that will be used for fertilization derive from the spermatocytes showing the highest rate of interstitial chiasmata. This supports the hypothesis that the cyclic variations in interstitial chiasma frequencies represent a mechanism to ensure an adequate level of variability in a given population. The above mentioned correlation between chiasma frequencies and steroia hormone concentrations suggests that the seasonal chiasma cycles are controlled by the same environmental and hormonal factors regulating the spermatogenetic cycle

Repetitive DNA and polyploidy in selachians

1. 1. The DNA reassociation kinetics have been studied in 6 selachian species: Raja asterias, Raja montagui, Dasyatis violacea, Torpedo marmorata, Torpedo ocellata and Oxynotus centrina. 2. 2. The results obtained show that the genomes of the two Torpedo, Dasyatis and Oxynotus are polyploid if compared with those of the two rays, though this finds no correspondence in the diploid chromosome number. 3. 3. The phenomena of polyploidization would often be followed by wide chromosome rearrangements and by a progressive divergence of the various repetitive DNA sequences. 4. 4. The existence of polyploidy in almost all the main superorders of living Selachians suggests that this mechanism of genomic evolution may have played an important role in the phylogeny of this class. © 1982

Repetitive DNA and polyploidy in selachians

1. 1. The DNA reassociation kinetics have been studied in 6 selachian species: Raja asterias, Raja montagui, Dasyatis violacea, Torpedo marmorata, Torpedo ocellata and Oxynotus centrina. 2. 2. The results obtained show that the genomes of the two Torpedo, Dasyatis and Oxynotus are polyploid if compared with those of the two rays, though this finds no correspondence in the diploid chromosome number. 3. 3. The phenomena of polyploidization would often be followed by wide chromosome rearrangements and by a progressive divergence of the various repetitive DNA sequences. 4. 4. The existence of polyploidy in almost all the main superorders of living Selachians suggests that this mechanism of genomic evolution may have played an important role in the phylogeny of this class. © 1982