BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: reproduction

A New Mosquitoes Exterminator: CRISPR

Mosquitoes might be just pesky little insects that might start appearing again in a few months. They leave their saliva in your skin, and this causes an itchy bump. But in other parts of the world. Estimates report that mosquitoes have killed up to 52 billion people in history by spreading malaria, yellow fever, and dengue. It is currently killing 1 million people per year, even with advanced medicine and healthcare around the world. Doesn’t that horrifying statistic shock you? 

Aedes aegypti

A close shot of Aedes aegypti

To drastically lower this number, researchers took a smart approach and decided to eliminate the source of the problem. They decided to use CRISPR to genetically alter the male flies so that they become sterile.  Professor Craig Montell from UC Santa Barbara altered the gene of Aedes aegypti, the main type of mosquito that transmits dengue, yellow fever, Zika, etc. 

Previously, scientists just radiated and applied chemicals to sterilize male mosquitoes in hopes to alter their genes since “there are enough genes that affect fertility that one will likely be altered,” making them infertile. However, this would leave, many of the mosquitoes to be sick and die prematurely since other genes that don’t relate to fertility are also changed.

Using CRISPER/Cas9, researchers removed B2t, a gene that specifically affects male fertility in mosquitoes. Unlike in previous efforts, the sterile mosquitoes were completely healthy. 

This whole effort to sterilize insects is part of a greater method called the sterile insect technique (SIT). Scientists release way more sterile insects than there exist in the wild. The population will crash as females will not be mating with a lot of males that are capable of making offspring. A benefit of releasing males instead of females is that males feed on nectar, not blood,  so it will not cause major disturbance to communities.

To sexually reproduce, a sperm cell must meet an egg. Each gamete is a haploid that has a single set of chromosomes. The sperm and egg combine to produce a zygote making it a diploid with a complete set of chromosomes. If a male is sterile, then they are not able to produce or release their sperm, making it impossible for those insects to reproduce.

The effect of this technique is more effective after each cycle, so when you release the same amount of mosquitoes after 3 cycles, the population change will be way more drastic. A downside to this is that sterile male mosquitoes need to be reintroduced after they die off since they cannot pass on their mutated gene.

Although researchers have successfully identified a way to isolate the gene and remove it to make male mosquitoes fertile, they still needed to find the optimal ratio of lab mosquitoes to wild type to ensure that they do not wipe out the species in an area since that has dramatic effects on the whole ecosystem. The researchers conducted many trials and found that, in a week, a ratio of about “5 or 6 sterile males to one wild-type male” decreased female fertility by 50% while, a ratio of 15:1 suppressed female fertility to about 20%, where it leveled off. So depending on the situation, they now release the more precise amount. 

I think that this is one of the brilliant uses of CRISPR, and it only goes to show how far we can go if we master this technique. An ethics question that this research brings up is, do humans have the right to wipe out an entire species just because it is causing harm to humans?

Hot Guppies?

photo by Silvana Gericke

photo by Silvana Gericke
http://en.wikipedia.org/wiki/File:Poecilia_reticulata_01.jpg#filelinks

In a recent article from Nature, researchers observed mating patterns in guppies. While most guppies are plain in color, a few male guppies are vibrant and have interesting color variation. In the lab at Weill Cornell Medical College, it was seen that these colorful males father the most offspring. This is due to negative frequency-dependent selection, or the “rare-male effect“. Because the colorful male guppies are rare, they are attractive to female guppies looking for a mate. The variation in color is an effect from the guppies’ genes. Theoretically, these color variations were supposed to be “normal” a long time ago, because of Darwin’s Theory of Evolution. Rather than conforming to the common pattern, the few males that are colorful show bright colors and diverse patterns. Apparently this is due to the rare male effect. Female guppies simply prefer rare guppies and do not care for the pattern.

Although the results prove this theory in the lab, the researchers were doubtful that this happened in a natural setting. Therefore, the scientists went to Trinidad to see the guppies in their wild setting. They collected the colorful males, numbered them and then released them. Next, they waited for the guppies to mate and then counted their offspring. They did this twice. The first brood showed that the rare male effect was present, but the second did not. The researchers questioned, even though the effect was present in the first brood of offspring, the staying power of this effect. The scientists believed that the effect’s purpose was to prevent insect, which hinders the evolution of the fish.

Why are the mating patterns of guppies so important? What can they help us with in future research?

Here are some articles to further your knowledge in mating patterns and evolution

https://www.sciencenews.org/blog/scicurious/hottest-guy-guppies-stand-out-crowd

http://www.nature.com/nature/journal/v503/n7474/full/nature12701.html

http://en.wikipedia.org/wiki/Evolution

 

 

Big Brains Come at a Cost?

Having a big brain can be great. Whipping your friends at trivial pursuit, acing every test you take, and flaunting your vast knowledge to the world. But what is the cost? Researchers recently reported in Current Biology on tests run on guppies

flikr
photo credits to iosonoadry

and discovered some evolutionary setbacks to large-brained guppies.

Through tests with large-brained and small-brained guppies, the scientists determined that a large brain can have adverse effects on gut size and reproductive output.

The reason behind this, and the reason why this is important for humans as well, is because of the amount of mass the brain has versus the amount of energy it requires. In humans, the brain accounts for only 2 percent of the total body mass but makes up 20 percent of the energy requirement of the body. As Niclas Kolm said  “It is a remarkably costly organ energetically.” The idea is that there is a tradeoff between the brain and other organs, and as the brain gets bigger and requires more energy, the other organs must get smaller.

The group’s research suggest that humans and primates, animals with large brains, have relatively small family size because of the tradeoff between brain size and reproduction ability.

Thoughts?

http://www.biologynews.net/archives/2013/01/03/big_brains_are_pricey_guppy_study_shows.html

Odd Little Species Survives Without Sex

Of the two million know species on Earth, only about two thousand reproduce entirely asexually. Scientists think this is because organisms that reproduce without sex – which provides healthy genes from one parent that act as a template to repair mutated genes, leading to “theoretically healthier offspring” – are unable to mitigate the deleterious effects of gene mutation, which leads to their extinction. The bdelloid, a tiny, all-female, sea creature with a name that means “leechlike” for the way it moves, however, has survived for tens of millions of years without sex. In fact, they have diversified into more than four hundred species.

Researchers at the Marine Biology Laboratory in Woods Hole, MA wanted to find out why the bdelloid had avoided extinction, so they zapped some of the creatures with gamma radiation, which breaks up DNA. Oddly, the bdelloids did not succumb to the exposure even as the scientists pushed the radiation levels far past what would naturally occur on earth. When the mystified biologists examined the bdelloids’ DNA, they discovered that an early mutation had copied the entire genome, giving each organism four copies as opposed to the common two, which allowed it to repair severely damaged DNA. This mutation turned out to be beneficial for the aquatic creatures because it allows them to survive desiccation, a danger for bdelloids because of their transient underwater habitats.

More recently, scientists at the University of Cambridge published a paper in the journal PLoS Genetics recounting their discovery that about ten percent of the bdelloid’s genome is composed of alien DNA amassed through the consumption of bacteria, fungi, and algae. These foreign genes become active when a bdelloid dries out, and are thought to be partly responsible for the creature’s incredible ability to survive dehydration. Those same genes might also be behind “powerful antioxidants that protect bdelloids from the by-products of drying out”.

Evolutionary biologists are hopeful that a better grasp of the mechanisms that allow bdelloids to survive will lead to much greater discoveries such as how sex evolved. Matthew Meselson, a geneticist at Harvard University, said in an interview with LifeScience that “being able to understand how animal cells can be so resistant to radiation may be of some interest in understanding how [cancer, aging, and inflammation, of which DNA damage and repair are factors] might be inhibited in human cells.” Further experimentation could uncover new treatments that prolong life or fight cancer.

Mouse Stem Cells Become “Grandparents”

Copyright: Anne Burgess

Recently, researchers at Kyoto University in Japan were able to induce stem cells of rats to become viable eggs, which were then implanted in surrogate mothers. The resultant offspring were fertile, anatomically intact rats that were bred for additional generations, their ancestor being only a cell in a petri dish. This discovery has excited scientists the world over because it marks the first step towards making eggs for infertile humans or gays and lesbians.

 

The scientists at Kyoto began by taking female embryonic cells and “induced pluripotent stem cells”, and then inducing them to become an early form of eggs. Induced pluripotent stem cells (iPSCs) are adult cells that have been reprogrammed to express certain genes that make them effectively embryonic cells. There is some debate as to whether iPSCs differ from embryonic stem cells taken from harvested embryos, but in this instance they acted identically to the conventional stem cells.

 

The immature eggs, called “primordial germ-like cells” or PGCLCs, were then surrounded by “female gonadal somatic cells” (cells usually found in an ovary) to create a reconstituted ovary. These constructed ovaries were implanted into surrogate mothers, where the PGCLCs matured into “germinal vesicle-stage oocytes” or early embryos formed during the primary oocyte stage of oogenesis (egg formation), which occurs before birth. The mice that had been implanted with these constructed ovaries eventually gave birth to fertile offspring, which were followed by a few additional generations.

 

Though scientists have called this discovery a major step forward in reproductive biology, the lead scientist on the Kyoto team, Dr. Hayashi, cautioned: “it is impossible to immediately adapt this system to human stem cells” for a number of reasons scientific and moral. Creating egg cells from stem cells in humans could allow menopausal women to conceive, which brings its own set of moral quandaries as well. Ronald Green, a bioethicist at Dartmouth University, commented on NPR that one had to consider “the commercial possibilities of people selling to infertile people babies produced from George Clooney or Jennifer Aniston.” Evidently, the possibility that egg manufacture might one day be possible has sparked heated debate, but one must remember that it may only be speculation.

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