Aneuploidy and Natural Selection

Here is a paragraph to mull over:

Mis-segregation of cells (Image: Stefano Santaguida, Angelika Amon / MIT)Aneuploidy—the incorrect number of chromosomes in a cell—is extremely common in early embryos and is the primary reason for pregnancy loss. A report published today (April 9) in Science reveals that one cause of this aneuploidy—aberrant cell divisions in the embryo—is linked to a genetic mutation carried by the mother. Astonishingly, this mutation turns out to be very common and appears to have been under positive selection during human evolution.


Got nothin’ for this one. Not a clue in the world what sort of wise comment, wry twist, or bad joke goes here.


Image note: “Mis-segregation of cells”: (Image: Stefano Santaguida, Angelika Amon / MIT)

Williams, Ruth. “A Benefit of Failed Pregnancy?” The Scientist. 9 April 2015.


You Wouldn’t Believe ….

Now this is a paragraph:

Among the more profitable endosymbioses is one that allows the host to derive energy from sunlight. The light-harvesting machines of plants and algae, for example, are the products of an ancient merger between a photosynthetic bacterium and a microbial eukaryote. Like mitochondria, present-day plastids—including both pigmented light-harvesting as well as unpigmented nonphotosynthetic chloroplasts—are fully and inescapably integrated into the host cell. Their journey from bacterium to internal solar-powered generator is responsible for much of the success and diversity of life on earth; no other cellular invention has had a greater impact on eukaryotic evolution. In fact, as scientists continue to uncover new and bizarre plastid-bearing lineages, it is becoming clear that many eukaryotic groups lacking plastids actually descend from photosynthetic ancestors. Some species are even in the process of generating novel plastid organelles.


That is to say, just stop and consider everything in that paragraph.

Elysia chlorotica, for instance:

Elysia ChloroticaElysia chlorotica is a “solar-powered” marine sea slug that sequesters and retains photosynthetically active chloroplasts from the algae it eats and, remarkably, has incorporated algal genes into its own genetic code. It is emerald green in color often with small red or white markings, has a slender shape typical of members of its genus, and parapodia (lateral “wings”) that fold over its body in life. This sea slug is unique among animals to possess photosynthesis-specific genes and is an extraordinary example of symbiosis between an alga and mollusc as well as a genetic chimera of these two organisms.

(Encyclopedia of Life)

Is there really anything we can add to that? Behold … life!

Smith, David. “Steal My Sunshine”. The Scientist. January 1, 2013.

“Eastern Emerald Elysia”. Encyclopedia of Life. (n.d.)

Pierce, S. K., et al. “Horizontal Transfer of Functional Nuclear Genes Between Multicellular Organisms”. The Biological Bulletin. 204: 237-240. June, 2003.

Image credit: Patrick Krug via