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R Mikelsaar

Publications and source records attributed to R Mikelsaar.

7 recordsLinked to original sources
PubMed1987

A view of early cellular evolution.

Some recent puzzling data on mitochondria put in question their place on the phylogenetic tree. A hypothesis, the archigenetic hypothesis, is presented, which generally agrees with Woese-Fox's concept of the common origin of eubacteria, archaebacteria, and eukaryotic hosts. However, for the first time, a case is made for the evolution of mitochondria from the ancient predecessors of pro- and eukaryotes (protobionts), not from eubacteria. Animal, fungal, and plant mitochondria are considered to be endosymbionts derived from independent free-living cells (mitobionts), which, having arisen at different developmental stages of protobionts, retained some of their ancient primitive features of the genetic code and the transcription-translation systems. The molecular-biological, bioenergetic, and paleontological aspects of this new concept of cellular evolution are discussed.

Animals↗
PubMed1983

Human mitochondrial genome and the evolution of methionine transfer ribonucleic acids.

The recently deciphered sequence of the human mitochondrial genome is analyzed in the light of an archigenetic hypothesis, according to which mitochondria are derived neither from pro- nor eukaryotes but from more primitive organisms. The possibility that animal mitochondria have only one gene both for elongator and initiator methionine tRNA is supported but C-A pair forming cytosine in the anticodon of these tRNAs is considered to be unmodified. The evolution of the gene and of the codon reading pattern of methionine tRNA is discussed.

Animals↗
PubMedDate not supplied

Cytogenetic analyses in infertile men.

In order to assess the significance of chromosome abnormalities and polymorphic chromosomal variants in male infertility, the results of cytogenetic studies of 90 patients (32 azoospermic and 58 oligozoospermic men) were compared with those of 30 control fertile men in Estonia. Total chromosome alterations were revealed in 47.8% of infertile men. Major chromosomal abnormalities had a 10-fold increase (13.4%) in infertile males (15.6% in azoospermics and 12% in oligozoospermics) compared to the control group. In azoospermics, the most prevalent were sex chromosomal abnormalities (47,XXY)(12%), whereas a Robertsonian translocation, t(13;14) was found in one patient (3.1). In contrast, in the oligospermia group the most frequent abnormalities were autosomal (10%), of which 6.9% were translocations. Sex chromosomal abnormalities were found very rarely (1.7%). Incidence of chromosomal variants was high (38%), but similar in all groups. The most frequently observed polymorphisms involved chromosome 9. In conclusion, chromosomal abnormalities found with a high frequency in infertile males are a major cause of male infertility, and justify the requirement of cytogenetic analysis in every infertile man.

Adult↗