Selection-mutation balance in polysomic tetraploids: Impact of double reduction and gametophytic selection on the frequency and subchromosomal localization of deleterious mutations
Dv. Butruille et Ls. Boiteux, Selection-mutation balance in polysomic tetraploids: Impact of double reduction and gametophytic selection on the frequency and subchromosomal localization of deleterious mutations, P NAS US, 97(12), 2000, pp. 6608-6613
Citations number
49
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
We modeled the behavior of recessive mutations with deleterious effects to
either the sporophyte or the gametophyte, or both, in polysomic tetraploid
populations by allowing for varying levels of double reduction, mutation, a
nd self-fertilization. Double reduction causes a decrease of the equilibriu
m frequencies of deleterious alleles, and it has much more influence on gen
es subjected to gametophytic selection than on genes solely under sporophyt
ic selection. With gametophytic selection, low frequencies of double reduct
ion are enough to reduce equilibrium frequencies severalfold. Double reduct
ion occurs when sister alleles migrate to the same gamete during meiosis, I
t depends on the frequency at which a locus recombines with its centromere,
and on the frequency of multivalent formation. Therefore, a greater accumu
lation of deleterious mutations should occur on polysomic chromosomes with
a prevalence of bivalent pairing and in chromosomal regions between centrom
eres and proximal chiasmata. Proximal loci should have a greater impact in
reducing the fitness of a polyploid population being inbred. This predictio
n can explain observations that homozygosities at different subchromosomal
regions have distinct effects on inbreeding depression in polyploids. Furth
ermore, even mildly deleterious alleles can lead to large amounts of inbree
ding depression because of their high equilibrium frequencies. Molecular st
udies correlating level of heterozygosity and degree of heterosis should ta
ke into account this nonuniform distribution of deleterious alleles in poly
ploid genomes. Preservation or enhancement of heterozygosity would be more
critical at proximal regions than at other chromosome regions in polysomic
polyploid species.