Aphids, Family Aphididae

Plant-sucking aphids are the bane of a gardeners existence. Come spring, aphids appear as if by magic and begin draining the life out of tender plants. Their ability to reproduce, both sexually and asexually, is prolific. Description Aphid bodies are soft and pear-shaped. Though most often green or yellow, aphids come in a variety of colors, from red to black. Few aphids measure more than a couple of millimeters. An individual aphid would be difficult to spot, but since aphids feed in groups, their presence is usually noticeable. Up close, aphids resemble little muscle cars with a pair of tailpipes. Entomologists believe these abdominal appendages, called cornicles, secrete waxy lipids or alarm pheromones when the aphid senses a threat. The presence of cornicles is a common characteristic of all aphids. Antennae may have five or six segments, with the final segment ending in a thin flagellum. At their other end, aphids possess a cauda, a short, tail-like appendage centered between the cornicles. Aphids usually lack wings, though certain environmental conditions may cause winged forms to develop. Classification Kingdom - AnimaliaPhylum - ArthropodaClass – InsectaOrder – HemipteraFamily - Aphididae Diet Aphids feed on plant phloem tissues, sucking the sugary liquids from the host plants vascular system. Reaching the phloem is no easy task. Aphids feed using a straw-like proboscis that contains thin, delicate stylets for piercing plant tissues. In order to protect the stylets from damage, the aphid secretes a special fluid from them, which hardens into a protective sheath. Only then can the aphid begin feeding. Aphids need nitrogen, but phloem juices contain mostly sugars. To get adequate nutrition, aphids must consume an enormous quantity of phloem liquids. They excrete the excess sugars in the form of honeydew, a sweet residue left behind on plant surfaces. Other insects, such as ants and wasps, follow behind the aphids, licking up the honeydew. Life Cycle The aphid life cycle is somewhat complex. Aphids usually reproduce asexually, with aphid mothers giving live birth to their young. Sexual reproduction occurs just once per year, if at all. Just before winter, sexual females mate with males and then lay eggs on a perennial plant. The eggs overwinter. In warm climates or in greenhouses, sexual reproduction rarely occurs. Special Adaptations and Defenses Aphids are tiny, slow-moving, and soft-bodied – in other words, easy targets. Theyre far from defenseless, however. Aphids use both fight and flight, and everything in between, to protect themselves. If a predator or parasitoid approaches an aphid, it can react in a number of ways. Aphids will literally kick their attackers, with some serious aggression. In other cases, the aphid may just walk away, hoping to elude the trouble. Sometimes, the aphid does a stop, drop, and roll, and simply falls to the ground. Some aphid species employ soldier aphids to stand guard. Aphids also arm themselves with defensive weaponry. When a pursuing predator attempts to take a bite from behind, they can excrete a waxy lipid from their cornicles to fill the attackers mouth. Alarm pheromones broadcast the threat to other aphids or may summon protection from bodyguards of other species. If a lady beetle attempts to feed on it, a cabbage aphid will mix toxic chemicals within its abdomen to bomb the offender. Aphids also use bodyguard ants, which they pay with sweet honeydew excretions. Range and Distribution Both abundant and diverse, aphids mainly inhabit temperate zones. Aphid species number over 4,000 worldwide, with about 1,350 species in North America alone.

The Crucible of Abigail Williams - 1517 Words

The Crucible of Abigail Williams Abigail Williams is a very spiteful and bitter woman, but she has the biggest influence on the play with all the lies she tells about people being witches which are believed and cost some people their lives. Abigail is one of the most misunderstood characters because she is so good at lying that it almost seems like she is telling the truth. A crucible is a large test that one may face that may force them to make a controversial decision to benefit them or to hurt them. In Salem, Massachusetts in 1691 there were whispers of witch craft. To avoid it one has to make lies to save themselves. Abigail Williams is one of the most important people in this story because she tells by far the most lies because†¦show more content†¦In John Proctor’s house when John Proctor comes home from working in the fields Elizabeth discovers that John was with Abigail alone and does not trust him any more. Through Abigail’s lying and attempts to win John over she begins to draw John and Elizabeth apart. When she realizes that she has a chance to frame Elizabeth she accuses Elizabeth of witch craft, because she wants to accuse Elizabeth on the grounds of Elizabeth being angry about the affair John and Abigail ha. Her thinking was that if she could not have John then no one can. Abigail feels as if she has won Johns wife is in jail and she knows that John still has feelings for her, so she feels like she can take the place of Elizabeth. Little did Abigail know that John would fight to get Elizabeth back by forcing Mary Warren to confess that it was her poppet not Elizabeth’s and that the girls are lying about all the witch craft. In the court room Abigail wants to attempt to prove Elizabeth a witch John comes in with Mary warren. When Mary testifies that the girls were lying Abigail said Mary was lying then when Abigail begins to feel threatened by Mary testifying she lies about Mary sending her spirit down to atta ck her. This is a sign of Abigail feeling very nervous about her lies holding up during court so she lies again. Then almost like the leader of a clan whenShow MoreRelatedThe Crucible : Abigail Williams845 Words   |  4 PagesThe Crucible: Abigail Williams In Arthur Miller’s play, The Crucible, Miller demonstrated that it was Abigail’s flaws- lust, jealousy, and mendacity- that led her to be responsible the most for the tragedy of the witch-hunt in Salem. The Crucible focuses of the finding of young girls and a slave messing around in the woods, trying to conjure spirits from the dead. Rather than admit to their actions and face the consequences, the girls accuse everyone else of the crimes they were guilty of. AbigailRead MoreAnalysis Of Abigail Williams In The Crucible857 Words   |  4 Pages Arthur Miller’sâ€Å"The Crucible† takes place in Salem, Massachusetts in the early 1690’s. It’s very popular because parts of this story are based on real historical events. This book has a lot of conflict happening when the people of Salem are being accused of witchcraft. Witchcraft was a very serious case to puritans. They thought that the people being accused should be punished for â€Å"being in contact with the Devil†. The people would either hang or be held in prison until they confessed. The personRead MoreExamples Of Abigail Williams In The Crucible772 Words   |  4 PagesThe Crucible is a play about the Salem Witchcraft Trials. In the town of Salem, Massachusetts, ninety one people were accused of witchcraft. A group of girls were caught dancing in the forest one night which is what caused the witchcraft trials. The group of girls started accusing people of witchcraft and the ringleader of the group was Abigail Williams. Abigail Williams had an affair with John Proctor then accused his wife, Elizabeth Proctor, of witchcraft so she could be with him. Although JudgeRead MoreAbigail Williams In The Crucible Analysis731 Words   |  3 PagesBeing related to a priest doesnt mean you are a good person. Abigail Williams was the niece of Reverend Parris, but she was no Puritan. Arthur Miller understood and used this truth while writing his play, The Crucible. Abigail did some things that were not only unspeakable by Puritan standards, but also illegal at the time. She had Tituba use voodoo magic in an attempt to kill John Proctors wife, and had an affair with him while she was living there as a servant. To top it all off, she threatenedRead MoreAnalysis Of Abigail Williams In The Crucible950 Words   |  4 PagesIn â€Å"The Crucible† the story has taught us about how great and powerful fear can easily take over one another and show how people turn against one another just to protect themselves. One of the characters in the story has shown a great example of this and you can see the great evil that is inside of this person who just lets good innocent people die to protect themselves. Cruel and selfish is what you think or maybe it is the other way around for you. Maybe you think you got to do whatever you gotRead MoreCauses Of Abigail Williams In The Crucible797 Words   |  4 PagesIn The Crucible, by Arthur Miller, people are accused of witchcraft and put to death because they don’t admit to it. People believed that witches followed the devil instead of God and only worked for the devil. Many people were killed without hard evidence for witchcraft. Many characters can be accused of causing the many deaths of innocent people but Abigail and Governor Danforth take most of the blame yet people could also blame Reverend Hale as well. Abigail Williams is one of the mainRead MoreThe Crucible: the Evilness and Selfishness of Abigail Williams956 Words   |  4 PagesThe Crucible: The Evilness and Selfishness of Abigail Williams In Arthur Millers The Crucible, there is one character who, because of her selfish and evil ways, causes the destruction of many people in the town of Salem. This character is Abigail Williams. In the play, jealousy, and self- interest are the two characteristics that are seen constantly throughout the play. These characteristics pertain particularly to Abigail, and give a graphic description of her life, and how she dealsRead MoreTheme Of Destruction In The Crucible By Abigail Williams711 Words   |  3 PagesThe main cause of the destruction in The Crucible is Abigail Williams. From the beginning Abigail has shown no mercy except for herself, from accusing others to bringing a McCarthyist shadow over the whole village. Abigail starts off in the play trying to get rid of Elizabeth Proctor, as she is madly in love with John Proctor. By doing what was feared during that time; witchcraft. With being caught and Betty Parris unconscious, she quickly starts forming her lies. Left and right she is throwing incriminationsRead MoreMass Hysteria In Abigail Williams In The Crucible1470 Words   |  6 Pagesplays an important role in Salem in the late 1600s. For instance Abigail Williams one of the girls in the crucible that uses mass hysteria to exploit the people of Salem around her. Mass hysteria mean s a group of people who over exaggerate something and becomes a fear. According to a quote from Abigail Williams says †She is blackening my name in the village! She is tellingRead MoreAnalysis Of Abigail Williams s The Crucible 1342 Words   |  6 PagesThe main character I chose to analyze is Abigail Williams. Abigail is a very intelligent, manipulative, and cunning character in The Crucible. Some would call her the puppet master of the play, as she almost seems to have all of the other characters on a string, controlling their destiny with her sly and devious ways. A main example of this in the play, was her use of Mary Warrens poppet to manipulate and control Elizabeth Proctors fate. A poppet is somewhat of a voodoo doll, which Mary Warren

Chromosomal Aberrations free essay sample

Chromosomal aberrations are abnormalities in the structure or number of chromosomes and are often responsible for genetic disorders. For more than a century, scientists have been fascinated by the study of human chromosomes. It was not until 1956, however, that it was determined that the actual diploid number of chromosomes in a human cell was forty-six (22 pairs of autosomes and two sex chromosomes make up the human genome). In 1959 two discoveries opened a new era of genetics. Jerome Lejeune, Marthe Gautier, and M. Raymond Turpin discovered the presence of an extra chromosome in Down syndrome patients. And C. E. Ford and his colleagues, P. A. Jacobs and J. A. Strong first observed sex chromosome anomalies in patients with sexual development disorders. Advances in Chromosomal Analysis Identification of individual chromosomes remained difficult until advances in staining techniques such as Q-banding revealed the structural organization of chromosomes. The patterns of bands were found to be specific for individual chromosomes and hence allowed scientists to distinguish the different chromosomes. Also, such banding patterns made it possible to recognize that structural abnormalities or aberrations were associated with specific genetic syndromes. Chromosome disorders, or abnormalities of even a minute segment (or band) are now known to be the basis for a large number of genetic diseases. Chromosomal disorders and their relationship to health and disease are studied using the methods of cytogenetics. Cytogenetic analysis is now an integral diagnostic procedure in prenatal diagnosis. It is also utilized in the evaluation of patients with mental retardation, multiple birth defects, and abnormal sexual development, and in some cases of infertility or multiple miscarriages. Cytogenetic analysis is also useful in the study and treatment of cancer patients and individuals with hematologic disorders. The types of chromosomal abnormalities that can be detected by cytogenetics are numerical aberrations, translocations, duplications, deletions, and inversions. Chromosomal Aberrations Chromosomal abnormalities can result from either a variation in the chromosome number or from structural changes. These events may occur spontaneously or can be induced by environmental agents such as chemicals, radiation, and ultraviolet light. However, mutations are most likely due to mistakes that occur when the genes are copied as the cells are dividing to produce new cells. These abnormalities may involve the autosomes, sex chromosomes, or both. The disruption of the DNA sequence or an excess or deficiency of the genes carried on the affected chromosomes results in a mutation. Such a change may or may not alter the protein coded by a gene. Often, however, a mutation results in the disruption of gene functionality. The resulting altered or missing protein can disrupt the way a gene is meant to function and can lead to clinical disease. Only mutations occurring to the DNA in the gametes will potentially pass on to the offspring. Mutations appear in gametes in one of two ways. A mutation may be inherited from one of an individuals parents. However, a mutation may also occur for the first time in a single gamete, or during the process of fertilization between an egg cell and a sperm cell. In this case the mutation or change is often called a de novo mutation. The parents are not affected by the condition and are not carriers of the mutation. The affected individual will have this mutation in all of his or her cells and may be able to pass the mutation on to any offspring. Some common abnormalities and their resulting phenotypes are discussed below. Aneuploidy Aneuploidy is the gain or loss of individual chromosomes from the normal diploid set of forty-six chromosomes. As in structural anomalies, the error may be present in all cells of a person or in a percentage of cells. Changes in chromosome number generally have an even greater effect upon survival than changes in chromosome structure. Considered the most common type of clinically significant chromosome abnormality, it is always associated with physical and/or mental developmental problems. Most aneuploid patients have a trisomy of a particular chromosome. Monosomy, or the loss of a chromosome, is rarely seen in live births. The vast majority of monosomic embryos and fetuses are probably lost to spontaneous abortion during the very early  stages of pregnancy. An exception is the loss of an X chromosome, which produces Turners syndrome. Trisomy may exist for any chromosome, but is rarely compatible with life. Aneuploidy is believed to arise from a process called nondisjunction. Nondi sjunction occurs when chromosomes do not separate correctly during meiosis. The direct result is that one gamete will have an extra chromosome and the other will be lacking a chromosome. When these gametes are fertilized by a normal gamete, they have either an extra chromosome (trisomy) or are missing a chromosome (monosomy). Disorders Associated with Aneuploidy Three well-known autosomal chromosome disorders associated with trisomies of entire autosomes are sometimes found in live births. These are trisomy 21 (Down syndrome), trisomy 13, and trisomy 18. Growth retardation, mental retardation, and multiple congenital anomalies are associated with all three trisomies. However, each has distinctive morphological characteristics, which are presumably determined by the extra dosage of the specific genes on the additional chromosome. Down syndrome (chromosome 21) is the most frequent trisomy found in humans, and one of the most common conditions encountered in genetic counseling. General characteristics are mental retardation, distinctive palm prints, and a common facial appearance. The average life expectancy is now much greater thanks to improvements in medical care. Generally, individuals with Down syndrome have affable personalities and are able to be partially independent. The incidence of Down syndrome is about 1 in 800 children and is often associated with later maternal age (as may also be the case with other aneuploids). Down syndrome appears to be related to the difference in gamete formation (gametogenesis) between males and females. In females, oocytes are formed before birth and held in a static state until ovulation. In the case of older mothers, an oocyte may be in this stage for more than forty years, during which time environmental factors may affect the genetic material. In trisomy 13 and trisomy 18 patients, congenital abnormalities are much more severe. These individuals generally do not live much beyond birth. Both trisomy 13 and trisomy 18 result in syndromes characterized by specific dysmorphic features and severe organ malformations. In a ddition to trisomies involving the autosomal chromosomes, aneuploidy may also involve  the sex chromosomes. Two examples are Turners syndrome and Klinefelters syndrome. As mentioned previously, Turners syndrome is a monosomy involving the X chromosomes. Turners syndrome females possess forty-five chromosomes (45, X) as compared to clinically normal forty-six (46, XX). They are usually sterile and short in staturewith some neck webbing. Klinefelters syndrome patients have a trisomy involving the sex chromosomes and thus have forty-seven chromosomes (47, XXY). Klinefelters syndrome individuals are sterile males possessing some female characteristics. These chromosome abnormalities are of interest especially for their implications in infertility and abnormal development. Abnormalities of Chromosomal Structure Four types of structural changes may occur in chromosomes: duplications, deletions, translocations, and inversions. All may result when there is breakage of the chromosomes and a rejoining or loss of chromosome fragments. If the same broken ends rejoin, the chromosome becomes intact once again. The resulting effects of such events depend on how large they are and where they occur on the chromosome. Rearrangements may occur in many forms and are less common than abnormalities of chromosome number. The most common type of rearrangement is called a balanced translocation because the amount of genetic information within that cell is normal even though it is repositioned. Therefore the individual with a balanced translocation may appear normal. However, there will be a risk to the children of a carrier of a balanced translocation since that person is likely to produce unbalanced gametes (bearing too little or too much genetic information), and therefore the risk of having abnormal offspring is increased. Rearrangements such as aneuploidy may be found in all cells of an individual, or they may occur only in a percentage of an individuals cells. This latter condition is known as mosaicism. In general, mosaic individuals show a less severe expression of their syndrome than those with chromosome abnormalities in all their cells. Unbalanced Chromosome Rearrangements A rearrangement is considered unbalanced if it results in extra or missing information. Structural rearrangements may be caused by a number of factors  including chemicals, some viral infections, and ionizing radiation. Because the complement of DNA or genetic material in the chromosomes is greater or less than the complement of DNA in a normal set of chromosomes, there is likely to be abnormal development. Deletions A deletion is the loss of a segment of a chromosome. The amount of deleted material may be any length from a single base to a large piece of the chromosome. The result is a chromosomal imbalance, with the individual being monosomic or possessing half of the required genes present in a normal individual for the segment of DNA missing. Only small deletions are tolerated, and the effect on the individual will depend upon the size of the deleted segment and the number and functionality of the genes that are contained within it. Larger deletions and the deletion of an entire chromosome always result in nonviable embryos. Cri du Chats (cats cry) syndrome individuals have a deletion of the short arm of chromosome 5. Although they possess the usual signs of chromosomal anomalies, such as mental retardation and low birth weight, their appearance is not extraordinarily different from normal individuals. One peculiarity is that affected infants make an unusual cry resembling that of a cat, hence the name of the syndrome. Two other interesting diseases are Prader-Willis syndrome and Angelmans syndrome. In both cases, patients with these diseases possess a deletion in the long arm of chromosome 15. Interestingly, the deletion is in the same location, but the resulting syndrome depends on whether the deletion was in the maternal or paternal chromosome. Duplications Duplications also result from the reuniting of broken pieces of homologous chromosomes. In some cases the chromosome pieces rejoin in such a way that there is a doubling, or redundancy, of a portion of the chromosome. This changes the number of genes present and may result in a problem with health, development, or growth. Large insertions and deletions prevent the production of useful proteins. The effect of smaller insertions or deletions depends upon how many bases are involved. Sometimes an entire gene can be inserted (in duplications) or deleted. The effect depends upon where in the genome the changes occur and how many base pairs are involved. Inversions An inversion is the rotation of a broken chromosome segment in such a way that it rejoins the chromosome in a reversed state, or is flipped, end to end. Inversions are usually characterized by whether the centromere is included in the inverted segment. Inversions containing the centromere are called pericentric. Those not containing the centromere are called paracentric. Although an inversion does not change the overall content of cellular DNA and can be considered a balanced translocation, it can affect a gene at many levels because it alters the normal DNA sequence. The gene may not produce its corresponding protein at all, or a nonfunctioning protein may result. There is a common inversion seen in human chromosomes involving chromosome 9. A small pericentric inversion is present in approximately 1 percent of tested individuals. There appears to be no detrimental effect on the carrier, and it does not appear to cause miscarriage or unbalanced off-spring. Recurrence Risk Chromosomal aberrations may be inherited from a parent, and because of this many families seek genetic counseling in order to determine if a genetic disorder will recur in another member of the same generation or in generations that will follow. The family needs to know the genetic risk, also known as the recurrence risk, and any means by which transmission may be prevented. A recurrence risk will be calculated based on the accuracy of the diagnosis, the pedigree of the family, and the known genetic mechanisms of the disorder in question.