Jökull - 01.01.2004, Síða 13

Theories on migration and history of the North-Atlantic flora: a review
að úr suðri eftir síðasta kuldaskeið (ördeyðukenning-
in). Í lok 19. aldar var ördeyðukenningunni andmælt
og hugmyndin um miðsvæðakenninguna kom fram,
þ.e. að plöntutegundir hafi lifað af á íslausum svæð-
um sem stóðu upp úr meginísbreiðunni. Miðsvæða-
kenningin átti marga fylgjendur allt til seinni hluta
síðustu aldar enda var hún talin geta skýrt útbreiðslu
ákveðinna plöntutegunda við N-Atlantshaf, einlend-
ar tegundir í háfjallaflóru Skandinavíu og tiltekin út-
breiðslumynstur í flóru Íslands og Skandinavíu. Síðar
voru þessi rök gagnrýnd og t.a.m. sýnt fram á fleiri
mögulegar skýringar á útbreiðslu þessara tegunda. Á
síðasta áratug hafa verið notaðar nýjar rannsóknar-
aðferðir s.s. sameindafræðilegar aðferðir, ískjarnabor-
anir og frjókornagreining til að reyna að svara sömu
spurningum og vísindamenn í byrjun 20. aldar höfðu
varpað fram. Þessar nýju rannsóknir hafa gefið mikil-
vægar niðurstöður en gátan um uppruna og sögu flór-
unnar við N-Atlantshaf er þó enn óleyst.
Glossary
Apomictic groups reproduce asexually without meio-
sis or formation of gametes but nevertheless produce
seeds that are indistinguishable from normal sexually
produced seeds.
Chloroplast DNA (cpDNA) is a very useful marker
for the analysis of the late Quaternary history of an-
giosperms because in most angiosperms, cpDNA is
transmitted through the ovules, not pollen. This may
lead to less swamping through interpopulational gene
flow of the initial genetic structure, established during
refugial survival and/or at colonization.
Endemic species is one that evolved in and has re-
mained restricted to a particular area. In a sense, all
plant species are endemic since none has a global dis-
tribution but the term is usually reserved for species
with a small distributional range.
Polyploidy is a mutation like effect that duplicates
whole sets of chromosomes in plants. Polyploidy can
be divided into autopolyploids, which are composed
of multiple sets from within one species, and allopoly-
ploids, which are composed of sets from different but
related species.
Random Amplified Polymorphic DNA (RAPD) is a
molecular method, used to examine phylogeography
and genetic diversity within and among populations.
Self-compatibility refers to plants that are capable of
self-fertilization.
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