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The Evolution of Sex Chromosomes and Sex Determination Mechanisms in Stickleback Fishes (Gasterosteidae)

Urton, James, R (2011) The Evolution of Sex Chromosomes and Sex Determination Mechanisms in Stickleback Fishes (Gasterosteidae). PhD thesis, University of Washington / Fred Hutchinson Cancer Research Center.

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In many vertebrate species, a bipotential gonad develops into either testes or ovaries based on the action of an initial sex determination signal. Sex determination signals vary widely among species and can be genetic or environmental signals. Closely related species can have different sex determination mechanisms. Among species with genetic sex determination mechanisms, such rapid turnover is easily seen in species with independently evolved sex chromosome systems. However, the mechanisms by which sex chromosome systems and sex determination mechanisms turnover are poorly understood. Within the stickleback fish family (Gasterosteidae), at least five sex chromosome systems arose in the past 40 million years. However, we do not know the evolutionary relationships among these sex chromosome systems, nor do we know if the same sex determination gene is found in different stickleback sex chromosome systems. To help understand the evolutionary relationships among the stickleback sex chromosome systems, I undertook genetic and cytogenetic screens to map the ZZ-ZW sex chromosome system of the fourspine stickleback, Ape/tes quadracus, relative to the threespine stickleback, Gasterosteus aculeatus. I discovered that the A. quadracus ZZ-ZW sex chromosomes arose independently of the other stickleback sex chromosome systems. I also discovered one A. quadracus population with no visible sex chromosomes. To address whether sticklebacks share the same sex determination gene, we first wish to identify the sex determination gene in G. aculeatus, which has a XX-XV sex chromosome system. Thus, I designed and executed a high-throughput sequencing transcriptome screen and identified hundreds of genes that are differentially expressed between the sexes during the early stages of gonadal differentiation. These genes will shed light on how sexual differentiation pathways have evolved in the stickleback family and assist in the continued search for the G. acu/eatus sex determination gene. In addition, my screen confirmed the lack of a global dosage compensation mechanism for X chromosome genes in this species. These results will spawn future studies to understand how sex chromosomes arose in this family, how the gene content of sex chromosomes can change over time, and how dosage tolerance evolves in a complex vertebrate genome.

Item Type: Thesis (PhD)
Subjects: Cellular and Organismal Processes > Evolution
Molecules > Chromosomes
Depositing User: Craig Johansen
Date Deposited: 04 Oct 2011 22:45
Last Modified: 01 Mar 2012 18:37

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