Sara and Danielle to present at Student Seminar on Thursday (8.July) at noon in 106 BBE

Sara and Danielle will be presenting Student Seminar this week in 106 BBE at noon. I have asked the speakers to provide a brief overview for their talks. Hope to see you there!

Background for Sara’s talk

The existence of ancient asexual lineages in nature contradicts the current prevailing hypotheses regarding the apparent advantages of sexual over asexual reproduction.  Bdelloid rotifers are one such putative ancient asexual group.  Interestingly, meiosis-specific genes have been identified in the genomes of multiple bdelloid species, as well as in their facultatively sexual sister taxa, monogonont rotifers.  By establishing a mictic transcriptome in monogononts, I will generate an expectation for the molecular nature of sexual reproduction in bdelloids. In addition, I will determine expression patterns in bdelloids under various conditions, including response to ionizing radiation, desiccation, and ultraviolet radiation. This work will shed light on the role of meiotic genes in bdelloids, as well as examine the potential existence of meiosis and sexual reproduction in these putative asexuals.

Background for Danielle’s talk

The generation of haploid gametes is necessary for sexual reproduction and maintenance of consistent ploidy in a species.  This is achieved by meiosis, varying from mitosis in that it has two divisions; the reductional division (meiosis I) and the equational division (meiosis II).  One of the most notable features of meiosis is recombination; and while recombination can occur during mitosis, it is much rarer (Paques & Haber, 1999).  Meiotic recombination is a complex process involving many proteins that is initiated between homologous chromosomes which have been paired up and aligned with each other and are usually held close together by the synaptonemal complex (SC).  The SC is present in nearly all organisms which utilize recombination during meiosis, but is not necessary for recombination to occur in all species (Roeder, 1997). The SC forms during pachytene, keeping the homologous chromosomes close so that crossover of DNA can occur; it also helps in preventing crossover between sister chromatids (Garcia-Muse & Boulton, 2007).

Drosophila males proceed through meiosis without formation of synaptonemal complexes or chiasmata, and yet are able to produce viable sperm.  The chromosomes are already paired at the start of meiosis, then each chromosome and its homolog form a territory adjacent to the nuclear envelope where they are separated from other non-homologous chromosomes.  Homologs remain paired through prophase and metaphase I until separated during anaphase I.  Meiosis II then occurs in a similar fashion to other eukaryotes.  Synaptonemal complexes and chiasmata are, however, seen in Drosophila female meiosis; so the genes which produce the required proteins are present in the genome.  This brings up the question as to what benefits may exist in having achiasmatic meiosis and how did it come to be utilized?  Since chiasmata formation is a requirement for proper chromosome segregation in most organisms, Drosophila males must have an alternate way of ensuring correct segregation.  By discerning as much as we can about this process and how it evolved, we can better understand the process of meiosis as a whole.

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Posted on July 6, 2010, in Student Seminar and tagged , , , , , , , . Bookmark the permalink. Leave a comment.

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