New theory, embryo geometry, proposes explanation for how vertebrates evolved

A new theory aims to explain how the complex vertebrate body, with its skeleton, muscles, nervous and cardiovascular systems, arises from a single cell during development and how these systems evolved over time. The theory, called embryo geometry, is the culmination of nearly 20 years of work by a team of researchers and science illustrators.

The new theory is published along with illustrations -- or "blueprints" -- depicting how it applies to different vertebrate organ systems in Progress in Biophysics & Molecular Biology.

According to Neo-Darwinian theory, major evolutionary changes occur as a result of the selection of random, fortuitous genetic mutations over time. However, some researchers say this theory does not satisfactorily account for the appearance of radically different life forms and their rich complexity, particularly that observed in vertebrates like humans.

Epigenetics and the Evolution of Darwin’s Finches

The prevailing theory for the molecular basis of evolution involves genetic mutations that ultimately generate the heritable phenotypic variation on which natural selection acts. However, epigenetic transgenerational inheritance of phenotypic variation may also play an important role in evolutionary change. A growing number of studies have demonstrated the presence of epigenetic inheritance in a variety of different organisms that can persist for hundreds of generations. The possibility that epigenetic changes can accumulate over longer periods of evolutionary time has seldom been tested empirically. This study was designed to compare epigenetic changes among several closely related species of Darwin’s finches, a well-known example of adaptive radiation. Erythrocyte DNA was obtained from five species of sympatric Darwin’s finches that vary in phylogenetic relatedness. Genome-wide alterations in genetic mutations using copy number variation (CNV) were compared with epigenetic alterations associated with differential DNA methylation regions (epimutations). Epimutations were more common than genetic CNV mutations among the five species; furthermore, the number of epimutations increased monotonically with phylogenetic distance. Interestingly, the number of genetic CNV mutations did not consistently increase with phylogenetic distance. The number, chromosomal locations, regional clustering, and lack of overlap of epimutations and genetic mutations suggest that epigenetic changes are distinct and that they correlate with the evolutionary history of Darwin’s finches. The potential functional significance of the epimutations was explored by comparing their locations on the genome to the location of evolutionarily important genes and cellular pathways in birds. Specific epimutations were associated with genes related to the bone morphogenic protein, toll receptor, and melanogenesis signaling pathways. Species-specific epimutations were significantly overrepresented in these pathways. As environmental factors are known to result in heritable changes in the epigenome, it is possible that epigenetic changes contribute to the molecular basis of the evolution of Darwin’s finches.

Continue reading at Genome Biology and Evolution (Oxford Journals) using link below:

Gibbon genome sequencing sheds light on rapid chromosomal rearrangements

Excerpt from New Scientist report:

Gibbons have such strange, scrambled DNA, it looks like someone has taken a hammer to it. Their genome has been massively reshuffled, and some biologists say that could be how new gibbon species evolved.

Gibbons are apes, and were the first to break away from the line that led to humans. There are around 16 living gibbon species, in four genera. They all have small bodies, long arms and no tails. But it's what gibbons don't share that is most unusual. Each species carries a distinct number of chromosomes in its genome: some species have just 38 pairs, some as many as 52 pairs.

"This 'genome plasticity' has always been a mystery," says Wesley Warren of Washington University in St Louis, Missouri. It is almost as if the genome exploded and was then pieced back together in the wrong order.

To understand why, Warren and his colleagues have now produced the first draft of a gibbon genome. It comes from a female northern white-cheeked gibbon (Nomascus leucogenys) called Asia.

Cut and paste DNA

Inside the genome, Warren and his colleagues may have identified one of the players responsible for the reshuffling. It is called LAVA, and it is a piece of DNA called a retrotransposon that inserts itself into the genetic code. Seemingly unique to gibbons, LAVA tends to slip into genes that help control the way chromosomes pair up during cell division. By altering how those genes work, LAVA has made the gibbon genome unstable.

"We believe this is the driving force that causes, for want of a better word, the 'scrambling' of the genome," says Warren.

However, solving this mystery has created another. Such dramatic genome changes are normally associated with diseases such as cancer, and should be harmful. "It's a complete mystery still how these genomes are able to pass from one generation to the next and not cause any major issues in terms of survival of the species," says Warren.

It may be that genomes are much more resilient than anyone expected, saysJames Shapiro at the University of Chicago. "The genome can endure lots of changes and still function."

Continue reading at New Scientist using link below:

Making new species without sex: Plants can transfer their entire genetic material to a partner in an asexual manner

Plants can transfer their entire genetic material to a partner in an asexual manner, researchers report. Occasionally, two different plant species interbreed with each other in nature. This usually causes problems since the genetic information of both parents does not match. But sometimes, instead of passing on only half of each parent's genetic material, both plants transmit the complete information to the next generation. This means that the chromosome sets are totted up. The chromosomes are then able to find their suitable partner during meiosis, allowing the plants to stay fertile and a new species is generated. 

Experiment shows specific memories can be passed between generations

Study reveals how mice conditioned to dislike a cherry blossom odour passes on the aversion to successive generations by controlling how some genes are activated. The successive generations of mice were even born with more cherry blossom detecting neurons in their noses and more brain space devoted to smelling cherry blossom.

"In the smell-aversion study, is it thought that either some of the odour ends up in the bloodstream which affected sperm production or that a signal from the brain was sent to the sperm to alter DNA." (BBC News)

Cytoplasm Affects The Number Of Vertebrae In Carp-Goldfish Clones, not the genes

When the nucleus of a common carp, Cyprinus carpio was transferred into the enucleated egg cell of a goldfish, Carassius auratus, the result is a cross-species clone with vertebral number closer to that of a goldfish than of a carp but with more rounded body of a carp. The team behind the experiment conclude that the egg cytoplasm, and not the genetic code of the transplanted nucleus, influenced this aspect of the skeleton as the cloned fish developed.

Two related species of plants with different flower patterns have the same genes

The plant known as yellow toadflax (Linaria vulgaris) has bilaterally symmetric flowers. But a variant of the same plant has radially symmetric flowers. The variant was identified by Linnaeus in 1744 and he named it Peloria (Greek for monster). Now 250 years later, in 1999, Enrico Coen of the John Innes Centre, Norfolk, shows that the genes responsible for the flower shape (Cycloidea) have exactly the same DNA sequence in both plants. The difference in flower shape is an epigenetic factor and it alters how the genes are expressed. The interesting point is that such an epigenetic change is reliably been passed down through generations and it has done so for at least the 250 years since its first discovery.

DNA of tree different at top and bottom of the same tree

 "If a person were to climb a towering redwood and take a sample from the top and a sample from the bottom of the tree, a comparison would show that the two DNA samples are different. 

Christopher A. Cullis, chair of biology at Case Western Reserve University, explains that this is the basis of his controversial research findings."

"The controversy stems from the idea that the environment changes organisms as they grow and these changes are passed on." (Sciencedaily)

Single-celled slime mould solves maze puzzle

Be amazed by what a single-celled organism can do. The experiment was conducted by a team of Japanese scientists on the single cell slime mould.

"This remarkable process of cellular computation implies that cellular materials can show a primitive intelligence," the team writes in Nature.

Reference Archive


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