There’s an interesting discussion going on at Pharyngula regarding virgin birth in
Bethlehem Komodo dragons. Two captive females in Europe recently gave birth to clutches of eggs despite no to minimal contact with males. The progeny are all homozygous at the each of the seven loci surveyed, with alleles matching those of the mothers. The logical conclusion to be drawn is that the eggs arose via parthenogenesis — either by reabsorption of the second polar body or suppression of the second meiotic division.
Take note that this is not clonal reproduction — the progeny contain two copies of half of the mother’s genomic information, rather than an exact copy of her entire genome. That means the progeny are homozygous for all loci. Also, because Komodo dragons use a ZW sex determination system (females are ZW, males are ZZ) all of the progeny are male (because they are homozygous). Any WW zygotes are presumed to not develop to term.
But why isn’t there any heterozygosity? As mentioned above, the individuals have two copies of the sister chromatids, rather than two copies of homologs. Recall that in the first meiotic division homologous chromosomes segregate. Prior to that segregation, genetic exchange occurs between homologs. It is those recombination events which cause sister chromosomes to differentiate. This means that, even though homozygosity is extremely high in the diploid progeny from a parthenogenic birth, there should be some variation between sisters (which can be considered homologs in the progeny).
Either the researchers did not sample enough loci to find one of the heterozygous regions, or there really is no heterozygosity in the progeny. Does anyone know of any studies of recombination rates in Komodo dragons or closely related species? In mammals and Drosophila recombination is suppressed or non-existent in the heterogametic males. Has anyone looked at recombination rates in species with heterogametic females? Studies from other reptiles (or even other lizards) may not be appropriate due to the variation in sex determination systems amongst these species.
Sandy has more on the methods for determining that the babies arose via parthenogenesis. Additionally, there are concerns about the effects of parthenogenesis on genetic variation and sex ratios in the endangered natural populations of Komodo dragons.