Difference in evolutionary patterns of strongly or weakly selected characters among ant populations.

Despite being a central issue in evolutionary biology, few studies have examined the stasis of characters in populations with no gene flow. A possible mechanism of such stasis is stabilizing selection with similar peaks in each population. This study examined the evolutionary patterns of morphological characters with and without strong selection in ant populations.

The genome size evolution of medaka (Oryzias latipes) and fugu (Takifugu rubripes).

Evolution of the genome size in eukaryotes is often affected by changes in the noncoding sequences, for which insertions and deletions (indels) of small nucleotide sequences and amplification of repetitive elements are considered responsible. In this study, we compared the genomic DNA sequences of two kinds of fish, medaka (Oryzias latipes) and fugu (Takifugu rubripes), which show two-fold difference in the genome size (800 Mb vs. 400 Mb).

The DNA sequence of medaka chromosome LG22.

We report the genomic DNA sequence of a single chromosome (linkage group 22; LG22) of the small teleost fish medaka (Oryzias latipes) as a first whole chromosome sequence from a non-mammalian vertebrate. The order and orientation of 633 protein-coding genes were deduced from 18,803,338 bp of DNA sequence, providing the opportunity to analyze chromosome evolution of vertebrate genomes by direct comparison with the human genome. The average number of genes in the "conserved gene cluster" (CGC), a strict definition of "synteny" at the sequence basis, between medaka and human was 1.

Genomic organization of the sex-determining and adjacent regions of the sex chromosomes of medaka.

Sequencing of the human Y chromosome has uncovered the peculiarities of the genomic organization of a heterogametic sex chromosome of old evolutionary age, and has led to many insights into the evolutionary changes that occurred during its long history. We have studied the genomic organization of the medaka fish Y chromosome, which is one of the youngest heterogametic sex chromosomes on which molecular data are available. The Y specific and adjacent regions were sequenced and compared to the X.

Color reversion of the albino medaka fish associated with spontaneous somatic excision of the Tol-1 transposable element from the tyrosinase gene.

The medaka fish albino mutant, i(1) is one of the Tomita collection of medaka pigmentation mutants which exhibits a complete albino phenotype, because of inactivation of the tyrosinase gene due to insertion of a transposable element, Tol-1. Recently, mosaic black-pigmented i(1) medaka fish have arisen in one of our laboratory breeding populations. Their pigmented cells have been observed in all of the tissues, including the eye and skin, in which melanin is detectable in the wild type.

Comparative genomics of medaka and fugu.

A small freshwater fish medaka (Oryzias latipes) has been one of the most attractive experimental systems for research in genetics and developmental biology. We have formed an international consortium Medaka Genome Initiative (MGI) to collect and share various information and resources on medaka. The MGI has set an ambitious goal aiming at the complete sequencing of the medaka genome and as a feasibility study we have begun sequencing one particular chromosome, linkage group 22 (LG22) of approximately 22 Mb in size.