Brittanni+Ruck-Jessome

=Identical Twins and their Genetics=

December 20, 2012

====__Identical twins (Monozygotic):__ A single fertilized egg (zygote) divides in two to create two different embryos. Scientists have not yet discovered what causes the egg to split in two. Each twin then has similar genetic information because they are derived from the same egg. ====

====__Fraternal Twins(Dizygotic):__ Two separate eggs are fertilized by two different sperm. They are not genetically identical and or no more similar than siblings. They can be the same sex or different sex. Fraternal twins are the most common types of twins and “account for about 2/3 of twin pregnancies”(Iannelli, V. (1999).Facts about twins). ====



** to form fraternal twins. **
=Genetics of identical twins:=

====__Environment__: Environmental factors and factors that cause twins to look different based on what they are exposed to in the environment such as, if one twin spends more time in the sun or has an unhealthier diet. ====

====__Epigenetics__: There are chemical signals which tell a region of the genome to switch on or off at certain times. Epigenetics is the study of changes in gene expression. Twins can express genes at different times creating differences between them. National Geographic compares the epigenetic process to a piano “then epigenetic processes determine when and how each key can be struck, changing the tune being played” (Miller, P. (2012, January). National geographic). ====


 * media type="youtube" key="8zpYD-WjNDw" height="315" width="420" ||
 * **This video looks at the development of identical twins in the**
 * womb.****The****video explores the changes that twins go through**
 * and how their genetic** **information is affected.** ||


 * [[image:chrom.jpg]] ||
 * ** This picture shows the chromosome 3 pairs of in two sets of identical twins. In the three year old twins the **
 * epigenetic tags are in the same spot. In the fifty year old twins the epigentic tags are in different places, **
 * showing differences in this chromosome. ** ||

=
A study conducted at the University of Alabama at Birmingham (2008) shows that the genes of identical twins are different. Geneticist Carl Bruder studied 19 sets of twins looking for genetic differences. He found that the genes of identical twins differ at various points in the genome and at these points there were a different number of copies of a certain gene, called copy number variants. Every person is born with two copies of the same gene passed down from each parent but in copy number variants a region of the genome deviates from this rule. “These regions can carry anywhere from zero to over 14 copies of a gene”(Graham, S. (2005, July 05).Scientific american). This study can explain how one twin will have a disease or disorder while the other will not. An example of copy number variants in his study is when one twin suffered from leukemia. “One twin in Bruder's study was missing some genes on particular chromosomes that indicated a risk of leukemia, which he indeed suffered. The other twin did not” ((Graham, S. (2005, July 05).Scientific american)). =====


 * [[image:identical-twins-not-identical.jpg width="365" height="200"]] ||
 * **Twins look mostly identical on the outside, but at the **
 * genetic level there are differences. ** ||

__Separation of Twins__

An extreme case that shows eerie similarities in twins is The Jim Twins. In Ohio, 1939, two twins were separated as babies and given up for adoption. Jim Lewis and Jim Springer were raised by two different couples who both happened to name them Jim. In 1979 and age 39 the twins reunited and some shocking similarities were revealed.

 “Both men were six feet tall and weighed 180 pounds. Growing up, they'd both had dogs named Toy and taken family vacations in St. Pete Beach in Florida. As young men, they'd both married women named Linda, and then divorced them. Their second wives were both named Betty. They named their sons James Alan and James Allan. They'd both served as part-time sheriffs, enjoyed home carpentry projects, suffered severe headaches, smoked Salem cigarettes, and drank Miller Lite beer. Although they wore their hair differently—Jim Springer had bangs, while Jim Lewis combed his hair straight back—they had the same crooked smile, their voices were indistinguishable, and they both admitted to leaving love notes around the house for their wives.” (Miller, P. (2012, January). National geographic)

 Are these similarities just a coincidence or is the answer at the genetic level? Psychologist Thomas Bouchard, after hearing about the Jim Twins, took the brothers to his lab in Minneapolis to confirm their similarities. People argued that details were exaggerated, and many said it was just a coincidence that their lives followed similar paths. The Jim Twins case is another example of the nature vs nurture debate. These twins separated at birth suggests that similarities of behavior and lifestyle are due to to genetics. When you consider the infinite amount of variation of environmental factors the findings are indeed startling.


 * media type="youtube" key="Wd5Y3-F79LY" height="315" width="560" ||
 * **Journalist Lisa Ling working as a research assistant for Dr. Nancy Segal, who studies**
 * reunited twins,** **interview a set of twins who were separated at birth, to examine how**
 * they are different but similar.****This research will help scientists to discover what part**
 * of us is influenced by our genes and environment.** **Reuniting after 35 years, the twins**
 * already have a close bond. They have similar interests and fears,** **which would suggest**
 * these traits are influenced by genes.** ||

separated as babies. ||
 * [[image:Image-3-425x324.jpg width="345" height="242"]] ||
 * The Jim Twins who showed remarkable similarities after being

__References:__ [] [] [] [] []

__Pictures:__ [] <span style="font-family: Arial,Helvetica,sans-serif;">[] <span style="font-family: Arial,Helvetica,sans-serif;">[] <span style="font-family: Arial,Helvetica,sans-serif;">[]

<span style="font-family: Arial,Helvetica,sans-serif;">Further Reading:

<span style="font-family: Arial,Helvetica,sans-serif;">[] -Scientific American article that outlines the recent research in genetic differences in twins. <span style="font-family: Arial,Helvetica,sans-serif;">[]- National Geographic article that looks at why twins differ genetically. Tells the story of the Jim Twins and has fascinating portraits of identical twins. <span style="font-family: Arial,Helvetica,sans-serif;">[]- University of Utah article that looks at the environmental impact on the epigenome. Explains how twin studies help scientists to identify environmental and genetic impacts on twins.

<span style="font-family: Arial,Helvetica,sans-serif;">[]- Psychology Today article that explains the research looking into why twins differ.

Evolution- Speciation = = January 14, 2013

__How do new species form?__

Speciation is the formation of a new species. The new species forms from its original species by acquiring new characteristics better suited for the new environment. The original species has to separate at one point and a smaller population of that species could now be living in an entirely new environment or be limited reproductively Because of the small population, the animals with mutations to suit the new environment or change because of selected mating processes, will thrive and produce offspring with these traits. Over time the new population will keep changing as their gene pool is not as large as the original species. Eventually they will be a completely new species as they have changed so much. A very common example of speciation would be the finches that Charles Darwin studied on the Galapagos Islands. He noticed that the finches had different beaks according to which island they lived on, but they all appeared to be closely related. He concluded that they must have a common ancestor and the changes were due to natural selection. The finches could have been separated due to geographical isolation. Speciation can be caused by geographic, behavioural or temporal isolation.



__Allopatric speciation__- A large population of species is separated from the original through a geographic event which will cause speciatiation to occur because of the new environment the species is moved to.

__Peripatric speciation__- Like allopatric but a smaller population of the species is separated, the separated population only contains a few individuals. Because of the smaller gene pool changes will occur much faster causing a quicker speciation process.

__Isolation Mechanisms__

__Geographic Isolation__- When a species separates from each other due to geographical barriers. The barriers can be mountains, barriers of water, migration etc. A natural disaster such as a flood can also lead to geographic isolation by separating the species into two different ecosystems. The original population will continue to look relatively the same but the population that is in the new environment will begin to adapt and evolve new characteristics to help them survive. Changes in genetics of each population are passed on through reproduction. One population will have certain mutations that the other population will not. An example of geographic isolation is the formation of the grand canyon which caused a change in the squirrel population. There are two different species of squirrel that are separated by the Grand Canyon, the Kaibab squirrel and Abert squirrel. The squirrels are anatomically similar (similar body parts and shapes) but differ in colourings. The Kaibab squirrel has a black underbelly, tufts of fur on the ears and a white tail. Abet's squirrels have a grey coat, white underbelly and a red colour strip of fur that runs down their back.



__Behavioural Isolation__- This type of isolation occurs when two populations are capable of producing offspring together but they have different mating rituals and will only mate with their population which has the same behaviour and rituals. This can cause a species to separate. Many birds have different mating songs and will only mate with the birds that use the same songs.

__Temporal Isolation__- This type of isolation occurs when species mate at different times of the year or day. The species will remain separate because they are not reproducing.

These isolating mechanisms are all examples of reproductive isolation, when two populations cannot reproduce There are species that can reproduce but they will not produce fertile offspring. These animals are called hybrids. The liger, a cross male lion and female tiger is an example of reproductive isolation resulting in sterilization. A tiger and lion cannot mate naturally in the wild lions live in Africa and tigers are native to Asia. If they did live in the same environment the chances of mating would be low as each species tends to mate with their own species.



<span style="font-family: Arial,Helvetica,sans-serif;">__Observation of Speciation__- An experiment carried out by Diane Dodd showed how reproductive isolation could occur in fruit flies(Drosophila pseudoobscura). She took a population of fruit fly and isolated them into two groups and placed each in a separate tank. This simulated geographic isolation. One group of flies was fed startch based food and the other were fed a maltose(malt sugar) based food. The flies were observed over many generations and then exposed to each other to see if they would still mate. It was noted that "maltose flies" preferred other "maltose flies," and "starch flies" preferred other "starch flies.” (Understanding evolution). This was the beginning of reproductive isolation due to geographic isolation of the fruit flies. This experiment showed that speciation is a possible result of geographic isolation.

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<span style="font-family: Arial,Helvetica,sans-serif;">__Can species separate if there are no barriers?(Another type of speciation)__- A new species evolving without any barriers from a single species so they eventually become reproductively isolated is called sympatric isolation. It can be seen in plants where there is a change in the number of chromosomes of one species. The most common way is through polyploidy( twice the normal number of chromosomes). The plants are then in the same environment as the original species but they are reproductively isolated from them as they have more chromosomes. It is very uncommon in animals and many scientists are unsure about whether it actually occurs.

looks at hybrid species of these salamanders. || __References__
 * media type="youtube" key="YCoEiLOV8jc" height="315" width="560" ||
 * This video is an example of speciation through geographic isolation in California salamanders. The video also

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__Pictures__

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__Further Reading__

[]- This article looks at the observation of speciation in microbes.

[]- This webpage looks at sympatric speciation through the apple maggot flies and hawthorn flies. These flies live in the same environment but only chose mates within their species. How did these flies separate?

[]- This website provides a detailed explanation of speciation and various isolating mechanisms.

[]- This website explains speciation but it also looks into the different types of speciation and it also provides examples.

= = =__Endocrine Disruptors__=

January 24
<span style="font-family: Arial,Helvetica,sans-serif;">The endocrine system is a set of glands that release various hormones into the body to regulate or maintain homeostasis. When the endocrine system is functioning properly the body can function properly as well. The endocrine system releases hormones in response to the body's changes as well as environmental changes. Hormones released by the endocrine system interact with cells by binding to cells with specific chemical receptors to send the chemical message. Endocrine disruptors can interfere with this binding process.

__<span style="font-family: Arial,Helvetica,sans-serif;">How to endocrine disruptors affect the endocrine system? __

<span style="font-family: Arial,Helvetica,sans-serif;">Endocrine disruptors can be found naturally in the environment or human made. Many of these disruptors mimic certain hormones in the body. These disruptors can also block the functions of hormones, disrupt functions of hormones, alter the chemical messages hormones send, and even turn off the signals that hormones give. Disruptors can affect the body's natural function in negative ways. Many disruptors have been found to reduce fertility, increase obesity, cancers and endocrine disorders. Fertility and early puberty are very common now and these problems may be linked to the increase in endocrine disrupting chemicals.The endocrine system of animals is also being affected in terms of development and fertility. An example would be the increasing number of intersex fish and sterile male frogs. They affect wildlife by settling into bodies of water and accumulating there because many endocrine disruptors to not break down quickly.

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__<span style="font-family: Arial,Helvetica,sans-serif;">What are these disruptors? __

<span style="font-family: Arial,Helvetica,sans-serif;">These disruptors are usually human made chemicals. We are exposed by the food we eat, medicine, and cosmetic products. They are also found in our drinking water because they are hard to break down. We come in contact with endocrine disruptors every day such as pesticides, industrial chemicals, polychlorinated biphenyls used in electircal equipment, dioxins, phenols, phthalates and plant matter.

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<span style="font-family: Arial,Helvetica,sans-serif;">**Pesticides**- Pesticides are a great way to control insect population but they can be extremely toxic. Pesticides like DDT have been found to affect human health. DDT can accumulate in our fatty tissues and glands like the thyroid and adrenal and mimic certain hormones. It has been found to mimic female sex hormones and block male sex hormones.

<span style="font-family: Arial,Helvetica,sans-serif;">**Industrial Chemicals**- Dioxins and PCB's( polychlorinated biphenyls) are industrial chemicals found to be endocrine disruptors. PCB's occur in low levels in the environment and are found in electrical equipment and coolants for electric motors. These chemicals accumulate in the human body and remain for a long time. PCB's can interfere with the thyroid hormone and mimic estrogen which can lead to an increase in breast cancer. Women exposed to high amounts of PCB's such as industrial workers, have been found to have irregular menstrual cycles. Dioxins are released into the environment through the burning of industrial waste and can be ingested through meat and milk consumption. Dioxins can affect sperm counts in males, decrease testerone levels, decrease fertility in males and females and have been linked with the development of male breast cancer.

<span style="font-family: Arial,Helvetica,sans-serif;">**Phthalates**- These are a group of chemical substances used to soften plastic to make it flexible. They can be found in cosmetic products and children's toys. These chemicals mimic estrogen and have been linked to sexual development problems in males such as reduced sperm count, small testes, and fertility problems. They have also been linked to early puberty in both males and females. The European Union has banned them in children's toys and cosmetics and but it is still allowed for use in the United States.

__<span style="font-family: Arial,Helvetica,sans-serif;">Phenols and Controversy __

<span style="font-family: Arial,Helvetica,sans-serif;">-When we think of an endocrine disruptor the most common word that may come to mind is bisphenol A. Bisphenol A is used to make various plastics that are used to make water bottles, feeding bottles for babies, food storage containers, food packages and many other household items. We usually ingest BPA by consuming food from these containers and bottles. When BPA breaks down the molecules are released that can cause harmful effects on the endocrine system. Research has found the BPA mimics estrogen in the human body especially during fetal development. Because it mimics the female sex hormone estrogen, it can lead to abnormal sexual development. “ Laboratory studies conducted since the 1990s have noted that low-dose BPA exposure may be connected to abnormal penis development in males, early sexual maturation in females...,”(NationalGeographic,2008). Females are beginning puberty as early as 7 years old and it is hard not to wonder if endocrine disruptors, like BPA have something to do with it. BPA mimics estrogen by binding to the same receptors that estrogen would normally bind to. <span style="font-family: Arial,Helvetica,sans-serif; line-height: 1.5;">The controversy stems from the use of BPA in baby bottles, exposing young children to this endocrine disruptor. BPA has been banned in baby bottles by the FDA(Food and Drug Administration), but is still found in other bottles. Because of the increased awareness of BPA as an endocrine disruptor, many products are now BPA free. We feel better buying these products but these products contain replacement chemicals that mimic estrogen just as BPA does, like bisphenol S.

__<span style="font-family: Arial,Helvetica,sans-serif;">How to Reduce Exposure __

<span style="font-family: Arial,Helvetica,sans-serif;">While we can't completely eliminate our exposure to endocrine disruptors as they are found in the environment, we can certainly limit our exposure. We can avoid pesticide use in our yards, avoid fatty foods like cheese and meat because many endocrine disruptors accumulate in fatty tissue, limit our use of plastic products, and buy organic.



of endocrine disruptors. It also addresses how these disruptors affect wildlife and humans. ||
 * media type="youtube" key="qB-qA9KMsTE" height="315" width="420" ||
 * This video discuses the danger of endocrine disruptors and the many types

__References__

[] [] [|http://www.nrdc.org/health/effects/qendoc.asp#reduce] [] [] []

__Pictures__

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__Further Reading:__

[]- Scientific American article on the topic of BPA and its affects. Also touches on research that shows the dangers of BPA. []- Article on endocrine disruption and early menopause in women. Phthalates and PCB exposure might be linked. []- Article on endocrine disrupting pesticides and the blocking of the male sex hormone testerone. []- Chemicals that have replaced BPA may also be endocrine disruptors that mimic estrogen just like BPA.