endosymbiont

 Discovery of male-harming DNA mutation reinforces ‘mother’s curse’ hypothesis

There is new evidence that the “mother’s curse” – the possibility that moms may transmit genes to their children that harm their sons but not their daughters – holds true in animals.

Such a possibility arises because there are two independent parts of the genome in the eukaryote cells, which are found in plants and animals, and the two are locked in a “conflict-driven molecular arms race” that impacts human health and wellness. The lion’s share of the genome is located in the cell nucleus. But there is also a much smaller secondary portion located in the mitochondria.

According to the generally accepted theory, mitochondria were originally independent bacteria that developed an ability to tap highly toxic oxygen molecules as a powerful energy source. Eukaryotes lacked this capability, so some of them found a way to swallow the mitochondria’s ancestor without digesting it – converting it into an “endosymbiont,” an organism that lives within the body of another organism. Unlike the nuclear genome, which is built from a combination of father’s and mother’s genetic material, the mitochondrial genome is passed down exclusively from the mother. As a result, male offspring are an evolutionary dead end. While natural selection actively suppresses mutations in the mitochondrial DNA (mtDNA) that weaken females, there is no direct mechanism for weeding out those that weaken males: a situation that leads to the mother’s curse.

While natural selection actively suppresses mutations in the mitochondrial DNA (mtDNA) that weaken females, there is no direct mechanism for weeding out those that weaken males: the situation that makes the mother’s curse possible.

Maulik R Patel, Ganesh K Miriyala, Aimee J Littleton, Heiko Yang, Kien Trinh, Janet M Young, Scott R Kennedy, Yukiko M Yamashita, Leo J Pallanck, Harmit S Malik. A mitochondrial DNA hypomorph of cytochrome oxidase specifically impairs male fertility inDrosophila melanogaster. eLife, 2016; 5 DOI: 10.7554/eLife.16923

Mitochondria.Credit: National Institutes of Health

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These are Scaly-foot snail (Chrysomallon squamiferum), an iconic vent endemic gastropod known only from the Indian ocean deep-sea hydrothermal vents, at more than 2500 metres deep.

This unique snail species lives just beside black smokers that are churning out superheated water exceeding 350°C. Has also harnessed the power of chemosynthesis, housing endosymbiotic bacteria in an enlarged part of its gut. This produces the energy it needs. it has a food factory inside its body and doesn’t even need to feed! This is likely the reason it can grow to about 45mm in size, when most of its close relatives without endosymbionts are only 15mm or smaller.