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Evolution of sex chromosomes and sex-biased gene expression

Hatem, Gad (2017) BINP30 20161
Degree Projects in Bioinformatics
Abstract
Sex chromosomes are chromosomes that carry vital sex-determining genes. Different sex determination systems and sex chromosomes have evolved from autosomes independently in different taxa; nevertheless, they share strikingly similar characteristics. Sex chromosomes undergo somewhat unique evolutionary processes due to paucity in recombination and transmission through only one of the sexes. As a result, sex chromosomes play an important role in genomic conflicts, adaptation and even speciation. In general, most sex determining chromosomes, due to their lack of recombination and low population size, experience accelerated evolution and the accumulation of repetitive sequences which render them hard to study. Neo-sex chromosomes (sex... (More)
Sex chromosomes are chromosomes that carry vital sex-determining genes. Different sex determination systems and sex chromosomes have evolved from autosomes independently in different taxa; nevertheless, they share strikingly similar characteristics. Sex chromosomes undergo somewhat unique evolutionary processes due to paucity in recombination and transmission through only one of the sexes. As a result, sex chromosomes play an important role in genomic conflicts, adaptation and even speciation. In general, most sex determining chromosomes, due to their lack of recombination and low population size, experience accelerated evolution and the accumulation of repetitive sequences which render them hard to study. Neo-sex chromosomes (sex chromosome–autosome fusions) have been identified in different species and provide great opportunities for further understanding of sex chromosome
evolution. In this study, we have confirmed a previously reported neo-sex chromosome in the common whitethroat by applying differential allele expression analysis. Our results also indicate that the neo-sex chromosome has undergone several evolutionary processes manifested in elevated expression and higher single nucleotide polymorphisms (SNPs) content. Additionally, some SNPs suggest Z, W polymorphisms which may be confirmed by further functional studies. (Less)
Popular Abstract
The evolution of sex chromosomes

The number of animal species that use sexual reproduction as means of their lineage continuation is remarkably high. One reason of maintaining the sexual reproduction system by so many species is the benefits that it brings to the table against genetic mutations. The sexual reproduction system helps numerous species to withstand harmful mutations and help their ability to adapt to environmental changes and competition. The sexual reproduction system relies on having a pair of heterosexual individuals that not only may differ in their appearance but also in their genetic make-up. This difference in the genetic make-up is reflected in the distinct characteristics between males and females that produce... (More)
The evolution of sex chromosomes

The number of animal species that use sexual reproduction as means of their lineage continuation is remarkably high. One reason of maintaining the sexual reproduction system by so many species is the benefits that it brings to the table against genetic mutations. The sexual reproduction system helps numerous species to withstand harmful mutations and help their ability to adapt to environmental changes and competition. The sexual reproduction system relies on having a pair of heterosexual individuals that not only may differ in their appearance but also in their genetic make-up. This difference in the genetic make-up is reflected in the distinct characteristics between males and females that produce unique reproductive cells. The reproductive cells, sperms in males and egg in females, bare one particular chromosome each, which in combination, determine the sex of the conceived individual.

Sex chromosomes, in general, have evolved from “non-sex chromosomes” called autosomes. Additionally, and as a consequence of some distinct characteristics, sex chromosomes have been harder to study crippling our understanding of basic biological questions and relevant disorders such as sex-linked diseases. In this research project, we have used the common whitethroat bird as a subject of our study to understand sex chromosomes. One main reason for our choice is that several previous reports have given evidence of the existence of a “neo-sex” chromosome in the common whitethroat. This chromosome has formed recently between the original sex-chromosome and a part of an autosome by a process called chromosome fusion. Another important reason is that the “neo-sex” chromosome bares striking similarity to the sex chromosomes in humans, which gives a unique opportunity to further enhance our knowledge of sex chromosomes and their evolution in humans.

We have used 6 male and 6 female individuals in our study where we have analyzed parts of their genome to great detail using a technique called RNA sequencing. This has provided us with the ability to determine the number of genes that were expressed to varying levels between male and female individuals. Expectedly, the majority of these genes were located on the original sex chromosome and the “neo-sex” chromosome. Interestingly, the number of differences in the genetic sequences of genes located on the “neo-sex” chromosome was more than three times higher when compared to the genetic sequence differences of genes located on the original sex chromosome or other autosomes. This suggests that the “neo-sex” chromosome has already started undergoing evolutionary processes which can also lead to augmented differences between the male and female specific sex chromosomes. Our study helps our understanding of the evolution of sex chromosomes and also the processes with which male and female individuals obtain their divergent sex-related genetic make-up.


Supervisors: Björn Canbäck and Bengt Hansson
Master's Degree Project in Bioinformatics, 30 credits
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Hatem, Gad
supervisor
organization
course
BINP30 20161
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8925217
date added to LUP
2017-09-11 08:46:31
date last changed
2017-09-11 08:46:31
@misc{8925217,
  abstract     = {Sex chromosomes are chromosomes that carry vital sex-determining genes. Different sex determination systems and sex chromosomes have evolved from autosomes independently in different taxa; nevertheless, they share strikingly similar characteristics. Sex chromosomes undergo somewhat unique evolutionary processes due to paucity in recombination and transmission through only one of the sexes. As a result, sex chromosomes play an important role in genomic conflicts, adaptation and even speciation. In general, most sex determining chromosomes, due to their lack of recombination and low population size, experience accelerated evolution and the accumulation of repetitive sequences which render them hard to study. Neo-sex chromosomes (sex chromosome–autosome fusions) have been identified in different species and provide great opportunities for further understanding of sex chromosome
evolution. In this study, we have confirmed a previously reported neo-sex chromosome in the common whitethroat by applying differential allele expression analysis. Our results also indicate that the neo-sex chromosome has undergone several evolutionary processes manifested in elevated expression and higher single nucleotide polymorphisms (SNPs) content. Additionally, some SNPs suggest Z, W polymorphisms which may be confirmed by further functional studies.},
  author       = {Hatem, Gad},
  language     = {eng},
  note         = {Student Paper},
  title        = {Evolution of sex chromosomes and sex-biased gene expression},
  year         = {2017},
}