Identification of Ampliconic regions on Zebra Finch Z Chromosome

Nitish Narula, Honors College biology student, submitted this abstract to the Annual Biomedical Research Conference for Minority Students.

Sex determination in mammals and birds is governed by sex chromosomes. Mammals have an X-Y sex chromosome system where males are XY and females XX. In contrast, birds have a Z-W system where males are ZZ and females are ZW. Finished sequences of avian and mammalian sex chromosomes have revealed the presence of large arrays of repeated segments, called amplicons. Amplicons are large, euchromatic, highly identical repeats. Ampliconic genes are predominantly expressed in the testis. Additionally, these regions evolve rapidly through gene acquisition, gene amplification and gene conversion. To study the evolution of ampliconic sequences in birds, we compared the genome of the zebra finch (Taeniopygia guttata) to the only other sequenced bird, the chicken (Gallus gallus). The chicken Z amplicon is 11 Mb long, comprising of 15% of the chicken Z chromosome and 1% of the total genome. It contains four families of genes that are expressed in the testis. We find that genes in the zebra finch that are homologous to those of the chicken Z amplicon are not amplified in the zebra finch genome. Instead, the zebra finch Z chromosome has independently amplified different sets of genes, consistent with the observation that amplicons are rapidly evolving. From these preliminary results, we predict that the zebra finch Z chromosome does have amplicons that have not been captured in whole genome shotgun (WGS) sequence. BAC-based finish sequencing will be necessary to reveal their structures. Given that genes in sex chromosome amplicons are predominantly expressed in the testis, these zebra finch Z ampliconic genes are likely to be involved in male fertility.