Reproductive mode of maternal backcross (BC-M) inferred from genotyping offspring of (<i>Hoc</i> x BC-M; Cross 1–3) and (BC-M x <i>Hoc</i>; Cross 4 and 5) using microsatellite DNA.

<p>In BC-M retaining two <i>Hoc</i> genome sets, alleles (orange) from hemiclonal hybrids (grandmother: <i>Hoc/Hag</i>) were inherited by offspring after recombination. Alleles (blue) from fathers (<i>Hoc</i>) are colored to facilitate discrimination.</p

Mitotic metaphase chromosome spreads and karyotypes of maternal backcross.

<p>(a) BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 1, (b) large metacentric chromosomes of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 2, (c)) large metacentric chromosomes and microchromosome of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 3; (d) BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) type 1, (e)) large metacentric chromosomes and microchromosome of BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) type 2. Arrow heads showed large metacentric chromosomes. The remaining spreads of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) and BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) were showed in S4 and S5, respectively.</p

The lineages of specimens used in this study.

<p>(a) artifial F₁-hybrids, (b) paternal backcross lineage, (c) maternal backcross lineage. All abbreviated species signs were referred to text. Yellow, light blue and purple of species signs indicate the <i>H</i>.<i>otakii</i>, <i>H</i>. <i>octogrammus</i> and <i>H</i>. <i>aggrammus</i> genome, respectively. Uncolored signs indicate species that not observed in this study.</p

Karyological observations of the three <i>Hexagrammos</i> species, and the natural hybrids and the artificial hybrids.

<p>Yellow cells indicate the most frequent chromosome numbers of each species and hybrid.</p

Mitotic metaphase chromosome spreads and karyotypes.

<p>(a) BC-M1 × <i>Hoc</i>; (b) <i>Hoc</i> × BC-M1.</p

Mitotic metaphase chromosome spreads and karyotypes of maternal backcross.

<p>(a) BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 1, (b) large metacentric chromosomes of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 2, (c)) large metacentric chromosomes and microchromosome of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) type 3; (d) BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) type 1, (e)) large metacentric chromosomes and microchromosome of BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) type 2. Arrow heads showed large metacentric chromosomes. The remaining spreads of BC-M1 ((<i>Hoc*</i>/<i>Hag</i>) × <i>Hoc</i>) and BC-M2 ((<i>Hoc*</i>/<i>Hot</i>) × <i>Hoc</i>) were showed in S4 and S5, respectively.</p

Schema of meiosis of natural hybrids and BC-M; (<i>Hoc*/Hag</i>) × <i>Hoc</i>.

<p>Figures of natural hybrids were cited from a putative description of chromosome elimination proposed by Ogielska (2009) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0180626#pone.0180626.ref020" target="_blank">20</a>]. Interphase to Anaphase I is included in the first meiotic division and Anaphase II in the second meiotic division. Large chromosomes are composed of a set of two chromosomes. In natural hybrids, the large chromosome appears to be transmitted intact without recombination to the gametes. However, in BC-M, the large chromosome becomes fissured into two chromosomes after segregation and recombination of genomes from the female and the male.</p

Mitotic metaphase chromosome spread and karyotypes.

<p>(a) <i>H</i>. <i>octogrammus</i>, (b) F₁-hybrid (<i>Hoc</i> × <i>Hag</i>), (c) F₁-hybrid (<i>Hoc</i> × <i>Hot</i>). Spreads of F₁-hybrids were showed in S1.</p