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Whitney Ginn
Techniques in Science
Analysis of Poeciliid Fishes Article
Lindholm, Anna. 2002. “Sex Chromosomes and Sexual Selection in Poeciliid Fishes”.
The American Naturalist . 160: S214-S224.
Poeciliid fish are able to give birth to live babies and whose species varies between their sex chromosomes and how they chose to select mates. This research paper goes into great depth about how certain traits are Y-linked in males, and how females are possibly attracted to certain traits located on a sex chromosome versus other similar traits.
These traits may not as unique as some of the other ones found on the sex chromosomes in other male fish. Also mentioned is how certain X-linked traits are more attractive to the females when presented on the male species due to crossover. Due to the preference of these traits on fish, certain fish may gain a positive advantage. Other male fish, however, will have a disadvantage because of their lack of a certain preferred sexuallylinked trait. In order to check this theory, studies comparing homogametic and heterogametic fish may help scientists understand how the male species have changed over time.
Much studying of gene mapping has to be done in order to prove the theory of physical linkage of genes and their effect on the female population. The frequency of certain physical traits showed that some characteristics could be beneficial to one sex and harmful to the other. Gathering on all this information, the Y chromosome is very possibly degenerating throughout time and evolution due to the lack of chromosomal information.

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Although this may be a possibility, females are certainly attracted to specific male traits. The characteristics researched showed certain species of fish had attraction to particular types of pigmentation, fin shape and size, as well as body size. Body size has not been shown to be sex-linked; therefore it has been omitted from the study. The experiment of the paper wants to see if the Y-linked traits affect the female’s preference because of the male’s phenotype.
In Lindholm and Breden’s experiment, an eight liter tank was acquired and filled.
One male guppy, which showed low-coloration, which was obtained from the Rio San
Miguel in Venezuela, was placed on one end of the tank, and another male guppy, was placed on the other end of the tank. The latter of the two male guppies is considered a high-coloration fish. He is known as an Endler’s live-bearer (ELB), who are known for their bright contrasting black and orange body patterns. This fish is also from Venezuela.
The female fish was bred from one parent of a highly colored fish and the other parent was one that was considered a low colored fish. A reciprocal cross was also performed, giving two types of F
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generation females. One female of these crosses was placed in the center of the tank. The three fish (one female, two male) were allowed to become adjusted to the environment for a few hours in the dark. A halogen light was placed above the tank, left for an hour so fish could reacquaint themselves, this time in the light. The twenty minutes afterwards was used for observation. This test was repeated a number of unmentioned times.
Statistics for the experiment showed that neither of the guppies of various color variation were not significantly different. For the low colored fish, there was no significant difference in the choosing of the males (X=0.05, N=11, P>0.2). However, for

3 the high coloration of the ELB males, there was a significant difference (X=0.66, N=11,
P<0.001). Taking these tests into consideration, it does show that the extent of the male coloration does have an affect on the female preference. When the researchers performed a backcross from the F
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generation, it showed that there was a regression back towards the parental preference (X=-0.07, N=7, low-coloration backcross, X=0.69, N=3, high coloration backcross). With these numbers the beginning of showing genetic linkage may occur, but with so few test numbers, it is not able to say for sure whether the linkage is true or not.
Research performed for this paper is excellent, however, very little of it seems relevant to the actual experiment. The experiment was very simple and straightforward, and could easily be done by any undergraduate. The scientists’ research goes into great detail about the Y-chromosome and how it may be degenerating and about how some of the genes may actually be X-linked. The experiment only goes into the simple observation of the preference between color, it does not go into how the genes may have been X-linked, and did not do any sort of comparison to the heavily talked about homogametic species of fish.
Another disappointment was that the researchers did not go at all into the gene mapping of their particular experiment. It is unknown which genes they observed and if these genes may have been X-linked and experienced crossover. Very little seemed to be known about what the actual experiment entailed. More research should have been done to pinpoint what the actual experiment dealt with. The record taking of the actual experiment had much lacking as well. The record of the F
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generation of the female fish was not mentioned, as well as how many times the experiment was performed and the

4 results of each individual experiment. All of this data would have been easily able to be put into a table.
The data collected from the experiment was indeed relevant to the hypothesis; however, the paper seemed to be more hype than anything. A possible way to make this experiment more relevant would have been to also test homogametic fish species preferences, and try to do some gene mapping between the two of them. Also, instead of just doing color, the researchers could have worked with other traits which have been known to sway the female preference, such as size, and characteristics dealing with the caudal fin. This may be helpful to see if there are certain male characteristics that are more attractive to females than others. It would be nice to see the scientists build on their research and try to find new and different results which support the other studies.
The review is able to be understood very easily. The words and context were not difficult to understand. A brief brush-up on certain terms may be required; however, the authors do include a short glossary which may aid the reader. Results of the two types of the research conducted were placed in two separate, easily understandable tables. The math is easy to understand, and organization of the paper is excellent.
The paper is interesting because of how it does try to show the physical linkage between genes and fish. Included in the table are a list of the Y-linked, X-linked, and the
X and Y-linked chromosomes divided into different genus of fish, and gives references to where more information could be found.
In conclusion, the paper is well written and easily able to be understood. If an undergraduate would want to copy the scientists’ experiment, there would be no problem.
The mathematical data would also be easy to reproduce and able to be expanded on. A

5 separate trial should be conducted with homogametic fish and try to see how the difference of gene placement would be between the homogametic fish and heterogametic fish. This paper should be recommended for a basic understanding of fish genes and their physical linkage, but not for a basis for another research project. The articles used for the author’s research for this paper would probably be more ideal for that situation. Yet, this would be a nice start for a basic synopsis of the sexual selection and sex chromosomes in fish for anyone.