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Because the gene-enzyme system forms a closed loop, it presents us with a classic chicken or egg conundrum: Which came first, genes or the protein enzymes they code for? While the details are still not fully worked out, discoveries over the past few decades have lead researchers to a surprising possible solution: What really came first? Genes that act as enzymes! The RNA World Hypothesis is the idea that before living cells, the genetic code, and the gene/protein cycle ever existed, chains of a chemical called RNA were forming naturally. Once formed, some of these chains were able to function as enzymes, and were even able to evolve by making copies of themselves with slight, accidental modifications.

The Aedes aegypti mosquito is the major vector for transmission of numerous viral diseases, including yellow fever, dengue, and now, Zika. Interestingly, different subspecies of A. aegypti are known to exist in close proximity but with considerable genetic divergence between them. One major difference between a "forest" form and a "domestic" form is a strong preference in the latter subspecies for human over non-human blood biting. This difference was explored with genetic and neurophysiological approaches by a research group at Rockefeller University and published in a 2014 paper in Nature. This flipped case study uses parts of the Nature paper to focus on elements of the scientific method as well as evolutionary questions raised by the difference in biting preference between the two subspecies. Students prepare for class by watching a video that provides background information about the published study that forms the basis for the case. In class students then work in groups to develop a hypothesis, predictions and proposed experiments to test the idea of different biting preferences.

In the study, published Monday (May 1) in Nature Biotechnology,  Luo and colleagues set their sights on two fusions genes they had previously found to be associated with prostate cancer and various forms of rapid and invasive cancer, including liver tumors. Using a modified CRISPR-Cas9 tool that creates a single- rather than double-stranded break in DNA, they targeted the chromosomal breakpoints that form these fusion genes and replaced fusion DNA with a gene encoding the enzyme HSV1-tk. This enzyme effectively kills tumor cells by converting the drug ganciclovir into its active form, which then blocks DNA synthesis and leads to cell death. (Ganciclovir is used to treat cytomegalovirus in humans.)

2:18 Human embryonic development depends on stem cells. During the course of development, cells divide, migrate, and specialize. Early in development, a group of cells called the inner cell mass (ICM) forms. These cells are able to produce all the tissues of the body. Later in development, during gastrulation, the three germ layers form, and most cells become more restricted in the types of cells that they can produce.

Through this method, the researchers were able to identify that the frizzled-6 gene was expressed around eight times more in tumor-forming cell lines. The specific cascade initiated by frizzled-6 and how it affects the development of cancerous cells has yet to be determined. The overexpression of frizzled-6 suggests that the protein either forms tumor cells directly or is an indirect result of other mutated pathways.

There are a significant number of genetics curriculum resources designed by different companies, curriculum development outlets, state curriculum designers and individual teachers. What resources are good? How do you know? As part of the Geneticist-Educator Network of Alliances (GENA) Project, a Curriculum Content Review Committee was formed to review readily available classroom resources about patterns of inheritance. Click here to see original evaluation form used by the committee and here to see the summary of the committee's review.

In the closing sentence of "The Origin of Species," Charles Darwin marvels at the process of evolution, observing how "from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved." Few people would describe bedbugs as most beautiful or most wonderful. Yet this blood-feeding pest may represent an exceptional chance to observe the emergence of Darwin's "endless forms": New research indicates that some bedbugs are well on their way to becoming a new species.

Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex? Before a meiotic cell divides, its two sets of chromosomes come together and cross over, or swap, segments. The first animation shows normal crossing over, where the X and Y chromosomes exchange pieces only at their tips. The second animation shows a rare mistake in which the Y chromosome transfers a gene called SRY to the X chromosome, resulting in sex-reversed babies. Studies of sex-reversed individuals led researchers to identify the master switch for sex determination, the SRY gene, which tells a fetus to become a boy.

Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex? Before a meiotic cell divides, its two sets of chromosomes come together and cross over, or swap, segments. The first animation shows normal crossing over, where the X and Y chromosomes exchange pieces only at their tips. The second animation shows a rare mistake in which the Y chromosome transfers a gene called SRY to the X chromosome, resulting in sex-reversed babies. Studies of sex-reversed individuals led researchers to identify the master switch for sex determination, the SRY gene, which tells a fetus to become a boy.

It's hard to escape childhood without racking up a few scars. Why do these leftover reminders of a painful cut or crash look different from the rest of our skin? And why do they stick around for so long after the incident that caused them? Sarthak Sinha explains how scars form.

As weather warms up off the coast of France, blooms of plankton have once again begun to form, creating a beautiful, multicolored swirl visible from space.

In the past, sailors on whaling ships would carve whale teeth into works of art in a process called scrimshaw. These pieces would be brought home to loved ones as mementos of the voyage. Design incubator Studio Swine is attempting to recycle found materials and turn this aged art form into a more sustainable practice. In this short film, travel to remote parts of the ocean, where "the closest people are in a space station," and watch as the process of collecting ocean trash and transforming it into beautiful treasure unfolds.

Dubilier is hardly alone in her plight. A heaping teaspoon of soil or a shot of ocean water may contain as many as one million bacterial species. Many of them are potential gold mines of chemicals and metabolites with medicinal, engineering, and energy applications. But when researchers have tried to culture these microbes in the lab, only a minority of cells form colonies. Clearly, nutrients, a carbon source, and time are usually not enough to coax bacteria isolated from the wild to grow in a laboratory setting. So what's the missing ingredient?

In this video Paul Andersen explains how the chloroplast in plants harnesses power from the Sun to form high energy molecules like glucose. The structure of a chloroplast as well as a brief discussion of the light reaction and Calvin cycle are included.

8' video on origins of life Paul Andersen describes how life could have formed on our planet through natural processes. The progression from monomers, to polymers, to protocells and finally to cells is described. The Miller-Urey experiment is described in detail as well as characteristics of the latest universal ancestor.

Darwin's theory of biological evolution helps us understand how simple life forms can give rise to complex lifeforms, but how did the first reproducing creatures come about? The origin of life needs its own explanation.

iKeepSafe is dedicated to the education of families on how to stay safe online. That's why we've teamed up with Google to develop curriculum that educators can use in the classroom to teach what it means to be a responsible digital citizen. The curriculum is designed to be interactive, discussion filled and allow students to learn through hands-on and scenario activities. Each workshop contains a resource booklet for both educators and students that can be downloaded in PDF form, presentations to accompany the lesson and animated videos to help frame the conversation.

Such descriptions of GMOs raises fears about whether gene transfer between species is outside of how evolution operates and therefore unnatural. Research, however, has repeatedly shown the opposite to be true. In May 2015, researchers showed that practically every known species of cassava (sweet potato) contained genes from Agrobacterium, a bacterial species whose genes we have also harnessed to create other GM crops. The genes were inserted over 8,000 years ago and may have helped the tuber evolve into its current, edible form. This phenomenon of genetic transfer during evolution between species, also known as 'horizontal gene transfer' is not restricted to plants.

Why do we smell different when we're sick? Why does cheese smell like feet? Why don't vultures get sick from eating rotting meat? Science is filled with stories: some of them are beautiful and some of them are gross. Really gross. Gross Science, a YouTube series hosted by Anna Rothschild, tells bizarre stories from the slimy, smelly, creepy world of science. In this collection, you'll find original short-form videos and DIY experiments from Gross Science, which is produced by NOVA and PBS Digital Studios. Learn about amphibians that eat their mother's skin, strange uses for bacon, how poop can be used to cure an infection, and more gross science topics.

Hybrid animals are infertile because of the way their sex cells form. But sometimes, life finds a way.

Fact sheet: Metastatic cancer is cancer that has spread from the place where it first started to another place in the body. A tumor formed by metastatic cancer cells is called a metastatic tumor or a metastasis.