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Ascorbic acid was given to CBA mice in drinking water (5%) a week before and during 35-day exposure to gamma-radiation from 137 Cs at a very low dose-rate (44 mGy/day). The frequency of micronucleated normochromatic erythrocytes (fMNCE) in peripheral blood was monitored by repeated sampling during the exposure. The analyses were made with flow cytometry giving a high resolution because of the large number of cells analysed, about 10(6) for each dose group and sampling occasion. Ascorbic acid in the drinking water did not modify the increase of fMNCE in the gamma-irradiated groups of mice, nor did ascorbic acid influence the fMNCE in the non-irradiated groups of mice.

The aim of this thesis is to evaluate the effects of Quaternary environmental fluctuations on the present patterns of mitochondrial DNA variation in the wood lemming, Myopus schisticolor, and the two genera of Arctic lemmings: collared lemmings, Dicrostonyx, and true lemmings, Lemmus.

The phylogeographic pattern and the limited mtDNA diversity in the Scandinavian populations of the wood lemming reflect recent colonization by a limited number of founders during the Holocene boreal forest expansion.

The mtDNA phylogeny in the two genera of Arctic lemmings gives no support for the existence of a single Beringian refungium since the mid Pleistocene. Isolation by intermittent inundation of the Bering Strait during the interglacials was most probably important for speciation in both genera, Dicrostonyx and Lemmus.

Comparative phylogeography of the two genera of Arctic lemmings, Lemmus and Dicrostonyx gives evidence for the vicariant separation by the glacial barriers in the Eurasian Arctic. There is genetic support for the importance of the Asian Beringia as a refugial area for the tundra specialist, D. torquatus, during warming periods in the interglacials.

There is no evidence for the direct effect of the last glaciation on the present level of mtDNA diversity and population structure in Arctic lemmings. Intrapopulation and intraregion mtDNA diversity estimates in each genus reflect the demographic events which were likely a result of environmental changes in the Holocene. Comparisons of mtDNA diversity estimates across the two genera of Arctic lemmings suggest that historically and presently codistributed Lemmus and Dicrostonyx responded differently to environmental changes resulting from the Holocene warming events in the Eurasian Arctic.

The mtDNA phylogeny supports the importance of vicariant events generated by the glacial-interglacial periods for allopatric speciation in chromosomally variable collared lemmings, Dicrostonyx, in the North America Arctic. In the Eurasian Arctic, the congruence between the phylogeographic structure in mtDNA variation and geographic distribution of chromosome races indicates that the fragmentation by the glacial barriers during the late Pleistocene and bottleneck events due to warming events in the Holocene were important for the origin of intraspecific chromosome races in the collared lemming, D. torquatus

Two chromosomal hybrid zones of the common shrew, Sorex araneus, have been investigated: the Hällefors-Uppsala hybrid zone in central Sweden and the Abisko-Sidensjö hybrid zone in northern Sweden. The Hällefors (Hä) and Uppsala (Up) chromosome races consisted of biarmed autosomes only (2nA=18), and differed in the Robertsonian fusions of two arms, ko, pq, and kp, oq, respectively. The Abisko (Ai) and Sidensjö (Si) races consisted of biarmed and uniarmed autosomes, and are mainly characterized by the fusions hn and hi, respectively. Robertsonian polymorphism was present in both races, affecting chromosomes g/m, h/n, i/p, j/l, kq, and j/l, k/q, n/r, respectively. The width of the Hällefors-Uppsala hybrid zone was 2.7 km and the center of the zone followed the Kolbäck river. The Abisko-Sidensjö hybrid zone had a width of 15.2 km in the area studied.

In the center of the Hällefors-Uppsala hybrid zone, one type of "complex" heterozygotes occured that formed a ring of four elements during meiosis. In the Abisko-Sidensjö hybrid zone, "simple" and "complex" heterozygotes ocurred which formed trivalents and/or a chain configuration of four/six elements during meiosis, respectively. There is no evidence from fertility studies that heterozygotes are less fertile than homozygotes, and the minor differences found in certain reproductive characters might be due to different genetic background rather than to chromosomal rearrangements. Microsatellite data demonstrated that gene flow occurs across the Hällefors-Uppsala hybrid zone, which is in agreement with the results obtained from the fertility analysis.

Mating structure and nestmate relatedness have been estimated in social Hymenoptera with different levels of sociality. Microsatellite markers have been developed for both communal bees (Andrena scottica) and for primetively eusocial wasps (Vespula rufa).

In the communal bee, Andrena scottica, females of the same colony are not related to each other suggesting that the lack of inclusive fitness payoffs may effectively constrain their social evolution. There was a positive inbreeding coefficient for both examined populations of Andrena scottica as a result of a high degree of intranidal mating. This inbreeding did not lead to extensive production of diploid males as would be expected on the basis of the CSD (complementary sex determination) system of the honey bee, and thus Andrena scottica either avoids "matched matings", (i.e. either or both sexes refrain from mating with an individual carrying the same sex allele) or the sex determination departs from the honey bee model.

The primitively eusocial wasp Dolichovespula saxonica is highly polyandrous.Queens (n=7) mated 4-11 times (mean 6.0) and the effective promiscuity, k_e was 3.30-9.14 (mean 4.81). This resulted in low average relatedness among workers (g_ww=30-0.40; mean 0.37). On the contrary Dolichovespula media queens from three colonies mated with one male only. All males (n=80) originating from four D. saxonica colonies were produced by the queen, in agreement with the genetical interests of both the queen and the collective worker force ("worker policing"). One D. saxonica colony includedboth workers and male sexuals of two matrilines.

Bombus hypnorum is a primitively eusocial bumble bee. Queens from 14 colonies had mated 1-5 times (mean 2.43) with an effective promiscuity of 1-2.8 (mean 1.40). Half of the colonies examined, inhabited alien workers. These workers could originate from an earlier nest usurpation event, and the colonies with such alien workers had on average a larger size. Alien workers together with polyandry results in high variation among colonies in sociogenetic organisation. Genetical data were consistent with the view that all males (n = 233 examined) were produced by a colony's queen, in conflictwith the collective worker interest.