Good evening all,
We've made it a point several times during class this term to highlight how behavioral knowledge could be applied to conservation efforts. Here's a link to a recent (and lengthy) discussion of how captive breeding in cheetahs has been enhanced by applying more-naturalistic methods than simply pairing together single males and females. It's quite striking the lengths to which breeders have gone in order to improve the success rate of their breeding programs!
Good evening all,
As I indicated during class on Wednesday, we will not meet for lecture tomorrow (Friday 22 Nov), but instead will consider some topical science news:
We finished one of our recent lectures by introducing the concepts of gene therapy and cloning. Both of these stem from the application of modern genetic methods, and both exist already - but not without controversy.
As described in your text, gene therapy is an attempt to correct defective or missing genes, by using viruses to insert them into a person's cells. It remains very controversial and of relatively limited use, because many of the risks and complications of the technique have yet to be overcome. Indeed, some human gene therapy trials have resulted in patient deaths, and few would say that the technique has been proven to the point at which broad use is possible. Still, for some people with very specific types of genetic defects, gene therapy has proven to be a lifesaver (literally). We can expect to continue to hear much about gene therapy in the years to come.
Related to gene therapy is the concept of gene editing. The goal of this technique is not to replace defective genes with normal copies, but rather to use enzymes to edit (correct) the defective genes in place (e.g., within the cells of the organism). Gene editing utilizes techniques more recent than those employed in gene therapy, so it has been tested, and used, relatively less. Thus, it was of great surprise to the scientific community last Fall when a Chinese scientist (He Jiankui) claimed to have performed gene editing on several artificially (in lab) created human embryos, and then to have implanted those embryos into female surrogates to carry the developing embryos until birth.
The technique of gene editing is new enough that, one year ago, the ethical guidelines governing its use had not been fully developed. Nonetheless, there was a general understanding that the technique was not to be used in human embryonic tissue, that would result in *all* cells in the body inheriting the edited gene. This understanding was very broad, but was not universal, and scientists in several countries did use (or attempt to use) the technique on human embryos, in the hopes of creating a gene-edited person - a "designer baby".
The scientific backlash against this first report of human embryonic (germline) gene editing was relatively swift, and relatively severe. The scientist who conducted these first trials has been stripped of his research position, and charged with violating his country's biomedical research laws. The infants (twin girls) were reported to have been born, but little is known about their condition. Some researchers have suggested that they are at risk of a shortened life expectancy because of the gene editing. The gene that was edited in these now-children is thought to promote resistance to HIV infection, but also seems to play other roles in cells.
The article I am forwarding here comes from a few months ago, when the investigations into this researcher and his colleagues was still in process. In particular, there were a number of scientists here in the U.S. who were implicated as having supported this work. The researchers here have generally been cleared of any wrongdoing, but significant questions remain about who knew what, and the motivations (money? fame? patent-able technology?) for their involvement. This article also includes links to a number of related stories, of which there are many.
It is worth noting that somatic (non-germline gene editing) is gaining ground as a very powerful and promising technique. This variant of gene editing does not change the DNA in every cell in one's body, but only in focal tissues (such as a single organ) that may be malfunctioning due to a defective gene. Indeed, news reports of the promise of this (more-limited) application of gene editing are also prominent in the recent news, including:
I suspect that your generation will be forced to come to terms with the promises and perils of gene editing - it seems both incredibly promising, and incredibly dangerous at the same time. Having a robust set of regulations and ethical guidelines will be very important. If you were faced with the opportunity to correct a gene in yourself, in a loved one, would you? That's a very difficult question to answer a the moment, as we do not yet have enough experience with the pros and cons of these techniques. But, the evidence is beginning to accumulate...
Here's wishing you all the very best Thanksgiving break - please be safe, rest, relax, eat, and enjoy.
Good morning all,
As I noted on Tuesday, we will not meet for lecture today. We have only one textbook chapter remaining, which we will save for our first meeting after the Thanksgiving break.
Instead of lecture today, I'll offer you a reading instead, one that encompasses several of our recent topics. In recent classes, we have considered the degree of cooperation and conflict between reproductive partners, as well as the signaling that occurs to influence each other. When sexual investment is strongly different between the sexes, we expect that sexual selection can drive exaggerated displays, enhance female 'choosiness' of mates, and promote unequal reproductive tactics. But, curiously, sexual displays also are common within pair-bonded species, in which males and females have equal (or nearly equal) roles and should be in cooperative agreement over parental investment, rather than in conflict. An explanation for this paradox has been lacking.
A very recent paper sheds some light on this problem, and present a mathematical model which supports the idea that inter-sexual signaling displays which originate to exploit a sensory bias in the signal receiver can evolve into a cooperative exchange, suggesting that sexual conflict can morph into sexual cooperation. This has significant implications for parental investment and care, as we've noted that the degree of sexual conflict is one of the primary drivers of sexual dimorphism in parental investment.
This paper was published in the Proceedings of the National Academy of Science (PNAS), our national body of 'science experts'. Election to the Academy is reserved for the top thinkers in one's field, and is a prestigious badge of honor. Their Proceedings journal publishes papers submitted by Academy members, as well as those that Academy members recommend for publication.
If you access this link from an IUP campus computer, you can obtain access to the full article and its associated material, through IUP library subscription. If you try to access the article from off-campus, you will be blocked. I've attached the PDF of the article, just in case.
The math of the authors' model is well beyond us. If we accept their model as being sound, it suggests that, instead of females being 'lured' into over-investment in their offspring by male displays, females instead evolve to require (or at least benefit from) the male display in terms of stimulating female condition/motivation to a level of investment which is optimal for the female (but less than that which is maximally optimal for the male). This causes males to remain invested in the pair-bond and their role in parental investment, and reinforces the pair-bond between mating partners. In a sense, the females are now requiring the males to remain present, remain attentive, and to offer displays, in order to ensure that their female partner is providing enough investment of her own.
As do many science journal, PNAS occasionally offers peer commentary on papers which are especially important, or especially difficult (this one is perhaps both). The associated commentary on this paper (link below, PDF attached), describes this result in the context of dove mating pairs, for which male stimulation of female reproductive condition is a well-understood and very necessary component to the reproductive cycle. Interestingly, as the commentary notes, the capitulation of this male-female exchange may ultimately be female self-stimulation of reproductive condition, a result which has been suggested to occur in doves. That may be the current evolutionary end-point to this exchange, but it also has the potential to serve as a type of an "escape clause", which males may now be selected to exploit. It would be interesting to see how much variation exists in this end-point, and whether males can benefit from females which perform more of their own reproductive stimulation.
I hope that you find this article interesting - it represent a nice, theoretical treatment of a difficult (= interesting) problem, and should set the stage for experimental work to come.
I hope that you all have an excellent Thanksgiving break - please be safe, rest, relax, eat, and enjoy. See you early in December for our last chapter.
Good morning all,
I'm sure that you have heard recent news about gene editing that was performed on two human embryos by a Chinese scientist, in an attempt to introduce resistance to HIV infection. His efforts only came to light after the children were born, and have been roundly criticized as 'crossing the bridge too soon' - there seems to have been little or no oversight of his work, and most geneticists agree that it is too early for us to consider human genome editing, before we better understand the risks, and the opportunities, it poses.
But, calls for a moratorium on this type of work are not universal - some believe that the time is now to proceed, and that the potential risks of waiting are greater than the potential for doing harm. Others say that this is simply scientific progress - messy, risky, but in the end, advancing our knowledge and capabilities. That this debate is prominent in the science literature is a sign that this is truly the cutting-edge of research and its application. I'm sure that we haven't heard the last on this issue, and I also am sure that in your lifetimes there will be increasing opportunity to perform exactly this kind of genome editing.
Think about children you might have in the future - would you edit their genomes to improve their health? Or to make them smarter? Or kinder? What if you could only choose one of these characteristics? What if improving one caused reductions in another? There is still much to learn, and much to discuss...
Hope that you all have had a great Break, and are ready for the second half of our semester! I have been taking care of our planaria, and they are almost ready for your evaluation.
Travel safely back to campus - see you on Wednesday.
In science education, we like to categorize - things are either "this way", or "that way". Simplifying the variety and pointing out the differences is a proven way to aid understanding, and "boiling things down" to their general features is usually also scientifically accurate - except when it isn't.
In our labs this term, we have talked about meiosis and chromosomes, how chromosomes are paired to give us our genotype, how genotype determines what gametes can be passed on, and how our alleles direct our phenotype. Much of those discussions, as is typical, are of a 'this-of-that' format - we either have this genotype or that one, this phenotype or that one. But exceptions to these general rules are interesting, and often enlightening.
Several weeks ago I sent you a news story about a bird that was spotted in Erie, PA that appeared to be a gynandromorph - a genetic mosaic of both male and female tissues. Gynandromorphs are rare, and form when something other than the normal pattern of gamete combinations, chromosome sorting, and cell division occurs during early embryonic formation.
This week, there is news of another, even rarer genetic variant, this time in humans: a semi-identical pair of twins. You are already familiar with identical twins, which form when a fertilized zygote splits into two genetically-equal cells that develop into separate individuals. Identical twins share 100% of their DNA.
You also know about fraternal twins, formed when two (separate) fertilized eggs, rather than one, develop at the same time. Fraternal twins share 50% of their DNA (on average), just like any two siblings born at different times from the same parents.
In this, case we have something different. Semi-identical (sesquizygotic) twins form when a single female egg is fertilized by not one, but two, male sperm. This early embryo divides and begins to develop into not one fetus, but two fetuses. These fetuses develop at the same time and are born as twins. In this case, though, they are predicted to share 75% of their DNA, because they share 100% of their mother's DNA and only 50% (on average) of their fathers DNA, which together average 75%. In the case reported here, the twins share a slightly higher value (89%).
It is likely that this unusual pattern of fertilization actually happens with some frequency, but that the early embryos do not typically survive. This chance occurrence will give geneticists a new data point in their ability to test hypotheses of genes and relatedness - no longer are all twins in their databases either 50% or 100% related, now there is a known 3rd possibility.
Have a great weekend -
Good morning all,
In our labs these past two weeks, we have explored the shuffling of chromosomes that occurs during meiosis, and how the alleles of the genes on the chromosomes get sorted into gametes, which then combine to give offspring unique genotypes (sets of chromosomes and alleles) and phenotypes (physical features). Some of our examples this week included our 'sex chromosomes', the X and the Y, which combine to give us female (XX) or male (XY) characteristics.
When we discussed the phenomenon of nondisjunction, we noted that sometimes things don't quite work according to plan, and that unusual chromosome numbers occur. How about when unusual chromosome combinations occur?
You may have seen a news story recently abut an unusual bird (spotted in Erie, PA) that appeared to be male on one side of its body and female on the other. This is likely to be a gynandromorph, an individual that has male chromosomes (genotype) and characteristics (phenotype) on one side, and female genotype and phenotype on the other side.
A few examples of gynandromorphy have been reported in animals over the years. They appear relatively normal (as male and female organs are generally the same), but their ability to mate and breed is likely very low (as male and female mating behaviors and reproductive structures are very different, of course).
This individual was spotted because, in this species (the Northern cardinal), male and female phenotypes are very obviously different in color (dimorphic). In most bird species, you can't tell females and males apart, as they look the same (monomorphic). It makes me wonder: how many gynandromorphs are out there, and we just don't know about them? And, does this occur in humans?
Have a great weekend -