Published online by Cambridge University Press: 19 May 2011
CYTOPLASMIC SELECTION MAY CAUSE NUCLEO-CYTOPLASMIC CONFLICT
Several authors have noted that the mixing of cytoplasm following gamete fusion may increase the potential for spread of deleterious cytoplasmic variants through a sexual population (Grun, 1976; Eberhard, 1980; Cosmides and Tooby, 1981). This argument assumes a lack of precise control of intracellular replication and subsequent lack of segregation of the cytoplasmic DNA at gametogenesis. The replication and transmission of nuclear genes is tightly regulated, ensuring no segregation of alleles at mitosis and a fair meiotic segregation in heterozygotes. Thus, in the words of Birky (1983), the nuclear genome is “stringent.” In contrast, cytoplasmic genomes are “relaxed”: multiple cytoplasmic genomes populate each cell; they can be replicated different numbers of times during a cell cycle (Clayton, 1982) and can be differently transmitted to daughter cells. Throughout this chapter I focus primarily on mitochondria as examples of obligate cytoplasmic organelles, but similar reasoning applies to other cytoplasmic entities like plastids in plants and vertically transmitted endosymbiontic bacteria. The relaxed regulation of mitochondrial replication and segregation increases the scope for within-individual selection among mitochondrial genomes. This may possibly result in the evolution of selfish mitochondrial variants that are able to acquire a within-individual transmission advantage while being harmful to the host organism. A transmission advantage of a selfish mitochondrial mutant could result from superior competitiveness in heteroplasmic cells, for example due to a higher replication rate resulting in numerical over-representation in zygotes.
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.