Comparison Between Mitosis and Meiosis Processes

Mitosis (along with the step of cytokinesis) is the process of how a eukaryotic somatic cell, or body cell, divides into two identical diploid cells. Meiosis is a different type of cell division that begins with one cell that has the proper number of chromosomes and ends with four cells—haploid cells—that have half the normal number of chromosomes. In a human, almost all cells undergo mitosis. The only human cells that are made by meiosis are gametes, or sex cells: the egg or ovum for females and the sperm for males. Gametes have only half the number of chromosomes as a normal body cell because when gametes fuse during fertilization, the resulting cell, called a zygote, then has the correct number of chromosomes. This is why offspring are a mixture of genetics from the mother and the father—the fathers gamete carries half the chromosomes and the mothers gamete carries the other half—and why there is so much genetic diversity, even within families. Although mitosis and meiosis have very different results, the processes are similar, with just a few changes within the stages of each. Both processes start out after a cell goes through interphase and copies its DNA exactly in the synthesis phase, or S phase. At this point, each chromosome is made up of sister chromatids held together by a centromere. The sister chromatids are identical to each other. During mitosis, the cell undergoes the mitotic phase, or M phase, only once, ending with two identical diploid cells. In meiosis, there are two rounds of the M phase, resulting in four haploid cells that arent identical. Stages of Mitosis and Meiosis There are four stages of mitosis and eight stages in meiosis. Since meiosis undergoes two rounds of splitting, it is divided into meiosis I and meiosis II. Each stage of mitosis and meiosis has many changes going on in the cell, but very similar, if not identical, important events mark that stage. Comparing mitosis and meiosis is fairly easy if these important events are taken into account: Prophase The first stage is called prophase in mitosis and prophase I or prophase II in meiosis I and meiosis II. During prophase, the nucleus is getting ready to divide. This means the nuclear envelope has to disappear and the chromosomes start to condense. Also, the spindle starts to form within the centriole of the cell that will help with the division of chromosomes during a later stage. These things all happen in mitotic prophase, prophase I and usually in prophase II. Sometimes there is no nuclear envelope at the beginning of prophase II and most of the time the chromosomes are already condensed from meiosis I. There are a couple of differences between mitotic prophase and prophase I. During prophase I, homologous chromosomes come together. Every chromosome has a matching chromosome that carries the same genes and is usually the same size and shape. Those pairs are called homologous pairs of chromosomes. One homologous chromosome came from the individuals father and the other came from the individuals mother. During prophase I, these homologous chromosomes pair up and sometimes intertwine. A process called crossing over can happen during prophase I. This is when homologous chromosomes overlap and exchange genetic material. Actual pieces of one of the sister chromatids break off and reattach to the other homolog. The purpose of crossing over is to further increase genetic diversity, since alleles for those genes are now on different chromosomes and can be placed into different gametes at the end of meiosis II. Metaphase In metaphase, the chromosomes line up at the equator, or middle, of the cell, and the newly formed spindle attaches to those chromosomes to prepare for pulling them apart. In mitotic metaphase and metaphase II, the spindles attach to each side of the centromeres holding the sister chromatids together. However, in metaphase I, the spindle attaches to the different homologous chromosomes at the centromere. Therefore, in mitotic metaphase and metaphase II, the spindles from each side of the cell are connected to the same chromosome. In metaphase, I, only one spindle from one side of the cell is connected to a whole chromosome. The spindles from opposite sides of the cell are attached to different homologous chromosomes. This attachment and setup is essential for the next stage. There is a checkpoint at that time to make sure it was done correctly. Anaphase Anaphase is the stage in which the physical splitting occurs. In mitotic anaphase and anaphase II, the sister chromatids are pulled apart and moved to opposite sides of the cell by the retraction and shortening of the spindle. Since the spindles attached at the centromere on both sides of the same chromosome during metaphase, it essentially rips apart the chromosome into two individual chromatids. Mitotic anaphase pulls apart the identical sister chromatids, so identical genetics will be in each cell. In anaphase I, the sister chromatids are most likely not identical copies since they probably underwent crossing over during prophase I. In anaphase I, the sister chromatids stay together, but the homologous pairs of chromosomes are pulled apart and taken to opposite sides of the cell. Telophase The final stage is called telophase. In mitotic telophase and telophase II, most of what was done during prophase will be undone. The spindle begins to break down and disappear, a nuclear envelope begins to reappear, chromosomes start to unravel, and the cell prepares to split during cytokinesis. At this point, mitotic telophase will go into cytokinesis that will create two identical diploid cells. Telophase II has already gone one division at the end of meiosis I, so it will go into cytokinesis to make a total of four haploid cells. Telophase I may or may not see these same sorts of things happening, depending on the cell type. The spindle will break down, but the nuclear envelope may not reappear and the chromosomes may stay tightly wound. Also, some cells will go straight into prophase II instead of splitting into two cells during a round of cytokinesis. Mitosis and Meiosis in Evolution Most of the time, mutations in the DNA of somatic cells that undergo mitosis will not be passed down to the offspring and therefore are not applicable to natural selection and do not contribute to the evolution of the species. However, mistakes in meiosis and the random mixing of genes and chromosomes throughout the process contribute to genetic diversity and drive evolution. Crossing over creates a new combination of genes that may code for a favorable adaptation. The independent assortment of chromosomes during metaphase I also leads to genetic diversity. It is random how homologous chromosome pairs line up during that stage, so the mixing and matching of traits have many choices and contribute to the diversity. Finally, random fertilization also can increase genetic diversity. Since there are ideally four genetically different gametes at the end of meiosis II, which one is actually used during fertilization is random. As the available traits are mixed up and passed down, natural selection works on those and chooses the most favorable adaptations as the preferred phenotypes of individuals.

Punk Subculture - 1702 Words

With the high pace of modernization since the 20th Century, people tend to be mechanized into living where they live. Concerned with the erosion of identify and distinct ways of life, large quantities of subculture emergedï ¼Å'especially in the late 1960s and 1970s. Bourdieu has already coined the term ‘cultural capital’ to explicate the cultural asserts available within society. As provided with unique habitus and subcultural production, diverse subcultures often distinct through different subcultural capitals. This essay will interpret the notion of ‘subcultural capital’ thoroughly and analyses how it assists subgroups differentiate themselves from other social groups, especially focusing on the punk subcultural capital and its contemporary†¦show more content†¦Influenced by this punk subcultural capital, the punks distinguished themselves from the mainstream code of behavior. The subcultural capital not only differentiated from the widely accept ed ‘popular culture’, but also discriminated themselves from the ‘high culture’ as well. Hebdige (1976) has argued that subcultural knowledge often include class consciousness. As a matter of fact, the assertion of subcultural distinction partly bases on the ideal of classlessness (Thornton, 1995). Storey also points out that the class divides indeed exist between the subculture and the elite culture (Forgan, 2002). Opposite from the high culture, which is often appeal to the taste of the elite class, the subcultural capital is always less class-bound and concerned more about the interests of lower class. Therefore, it shapes people’s dispositions against the dominate stereotypes, such as class, gender and religion. As an illustration, the punks can come from all works of life and the diversity help to develop the punk tastes and contributes to the accumulation of subcultural capital, these tastes may give a guide to punks preference. In this way, th e subcultural capital assists to develop its uniqueness. Last but not the least, the subcultural capital singularise the culture through practice on the subcultural production, which mainly are the music, fashion, art and literature. The subculture always identified by practice on these expressive forms underShow MoreRelatedSubcultures : Women s Punk2209 Words   |  9 PagesSubcultures: Women in Punk Punk is one of the most written and talked about music and political movements of the twentieth century. What perhaps makes punk special is the way a generation incorporated the attitudes and practices of the music into an entire subculture. 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In this essay I have decided to focus solely on the youth culture of punk, and the differences it has been subject to when the subculture first emerged compared to in a contemporary context. In doing this I have decided to include information about the emergence and origins of punk, features or style of the punk subculture, how the subculture has changed since its emergence, contemporary punk today and why it is apparent that the punk subculture has changedRead MoreThe Hot August Night Inside The Echo Essay191 4 Words   |  8 PagesThe band performing was Los Angeles punk rock band the Weirdos. The audience consisted of punk fans. The punk music genre, subculture, and style is often times ignored, ridiculed, or portrayed as a fad that young teenagers cling to as they search for their personality. Today, punk appears to have been either reduced to nothing more than a type of â€Å"edgy† fashion statement by people who most likely know nothing about the history or ethics of the music and subculture, or it has been depicted as groupsRead MoreCommercial Recuperation Essay1925 Words   |  8 PagesCommercial Recuperation Essentially what Hebdige is saying with his statement is that eventually a subcultures generic trademarks will cross over into the mainstream. This will in tern render the original intentions of subversion diluted pastiches of there former representations. The validity of this statement is interesting in two ways. Firstly are subcultures subversive qualities diluted through popularisation? And secondly and perhaps more importantly in terms ofRead MoreAn Alternative View On Punk Visual Language1308 Words   |  6 Pages Example Five – Sniffin’ Glue Punk Fanzine, Issue No. 2 Offering an alternative view on punk visual language that is outwith both cover art and fashion is the amateur ‘punkzine’ (punk fanzine) Sniffin’ Glue, in particular issue number two. This primary source is built on the foundations of DIY values. With low production costs, the punk fanzine was created using felt tip pens for headings and a type writer for some of the included articles. Rough sketches were included throughout with no value placedRead MoreThe Ways Punk Culture has been Used688 Words   |  3 PagesPunk has influenced and has been influenced by popular culture in a number of ways. Since the beginning of the subculture, major label record labels, haute couture, and the mass media have attempted to use punk for profit and popularity. Punk fashion is the clothing, hairstyles, cosmetics, jewelry, and body modifications of the punk subculture. Many punks use clothing as a way of making a statement. First days of punk took place in London in the middle of the 70’s. Young teenagers and rebel followers

Code of Sexual Ethics Free Essays

Human Sexuality Due: April 24, 2009 The value of a sexual code of ethics is very high in this day and age. It is extremely important to have a code of sexual ethics right now as the youth of this country and even the world more so, need to make sure that they know where they stand in this subject matter. My sexual ethics are influenced by my faith and family mostly but my ethics are also influenced by my friends and the different media around me. We will write a custom essay sample on Code of Sexual Ethics or any similar topic only for you Order Now It is important that all people have some sort of code of ethics because sometimes we need to know what it is we stand for. When you do not sit down and evaluate what your standards are when it comes to sex and your sexual ethics, it is very easy to be swayed into doing things that you do not believe in doing or that are unsafe for you as an individual. So know who you are and what you are comfortable with, otherwise you can find yourself in some tight situations. I hope that by writing my own sexual ethics it gives insight to help you and the next generations decide where they stand on these important matters. Firstly, I want to tell you what I think sex is. I would define sex as the penetration of a male’s penis into a woman’s vagina by heterosexual definition. Sex is a big deal. It is the most appealing, common and acceptable sexual behavior among heterosexuals. My belief is that sex should be used in the context of marriage exclusively by a man and a woman. I also believe that in order to have sex with someone it requires full trust, communication, and the ultimate commitment, marriage because when you choose to have sex with someone you also choose to give them a part of yourself as well. If you have these factors in your sexual interactions with your significant other than you do not have to worry about the stress and unhappiness that comes along with relationship that do not have commitment. Sex is enjoyable and a pleasurable experience and when you find that one person that you want to share yourself with it is one of the most emotionally, physically, and mentally connecting moments to your partner. I myself have never had sex but from my experience, I have seen too many friends think they are ready and find out that they are not. After the fact of sharing themselves with someone, a lot of them want to take that one moment back. But it can never be taken back. Disadvantages of being abstinent are that it requires a lot of restraint and self- discipline, clear communication with your significant ther and the risk of having unprotected sex if by chance the commitment you made with your significant other falls through. From my experience being abstintent is hard because you want to show your significant other some type of affection and let them know that you care but those things lead to others and you can find yourself struggling to remain abstinent as you promised. Advan tages are that there is no cost, no risk of pregnancy, and protection from STIs. I hope that you as my child choose to take abstinence. It would give you a chance to live life without the complications of what sex has to offer. My last sexual ethic is that oral sex (cunnilingus, fellatio) and anal sex (anilingus) are also forms of sex. A lot of people do not consider it to be so. Some couples use anal sex as a substitute for intercourse. Some couples who have made a decision to avoid intercourse either due to personal moral beliefs, not wanting to worry about getting pregnant, or the desire to wait until a later point in time for intercourse will decide to use oral/anal sex as a way of exploring sexual intimacy without actually having intercourse. But one thing that many people forget is that STIs are more easily spread through having sex in these methods. When it comes to oral sex especially, people run into the problem of the transmission of almost all STIs, including HIV, hepatitis B, and human papilloma virus. One can also damage the rectal walls allowing contact of the inserting partner’s semen with the receiving partners bloodstream. So I hope if you are trying to find an alternative for sex if you are not going to have you think twice because all these things are sex and they can still give you STIs. I am very lucky to have parents that are open and talk about all types of issues. Things that they were not afraid to talk about were about the issues of sex and much needed information I needed to know. I learned a lot of what I know about sexuality from them. I learned about dating and the importance of sex after marriage from them. They instilled the fact that I should wait for my soul mate and husband before I decided that I was going to engage in sexual intercourse. They also were open with the option of telling me that if I was to have sex before marriage I could use protection to keep me safe and they also discussed what kinds of protection there are. What has been helpful in helping me decide what I wanted as my sexual ethics is that I was always able to openly ask my parents questions and if they did not know the answer to my question they would research for me or buy me a book on the subject so that we could talk and discuss the subject. It was kind of difficult to write this paper because if I could just have one sexual ethic to write about it would be abstinence because you do not have to worry about pregnancy or STIs if you are not engaging in things of the sexual nature. Even though staying abstinent is hard and very difficult I definitely stand by it one hundred percent. I already knew where I stood when it came to my sexual ethics and what I believed you can and cannot do with an individual or significant other. But this paper gave me even more reason to believe what I believe because I got to see the pros and cons of everything and it further confirmed my decision to be the way I am. I do live by the principles I wrote for my children and I hope that they are not afraid to live by them in the future. I do not think my code will ever need revisions in the future because I am firm in what I believe in and I hope that my kids will believe in it too. How to cite Code of Sexual Ethics, Papers

Aids In Africa Essay Example For Students

Aids In Africa Essay As recently as 1990, there were some regions of the world that had remained relatively unscathed by AIDS. Today, however, there is not a single country around the world which has wholly escaped the AIDS epidemic. As the epidemic has matured, some of the developed nations which were hard hit by the epidemic in the 1980s such as the United States have reported a slowing in the rate of new infections and a stabilization among existing cases with lower mortality rates and an extension of post-diagnosis lifespan. However, despite the changing face of the global AIDS pandemic, one factor remains unchanged: no region of the world bears a higher AIDS-related burden than sub-Saharan Africa. This paper examines the demographic effects of AIDS in Africa, focusing on the hardest-hit countries of sub-Saharan Africa and considers the present and future impact of the AIDS epidemic on major demographic measures such as fertility, mortality, life expectancy, gender, age, and family structure. Althoug h the sub-Saharan region accounts for just 10% of the world’s population, 67% (22.5 million) of the 33.4 million people living with HIV/AIDS in 1998 were residents of one of the 34 countries of sub-Saharan Africa, and of all AIDS deaths since the epidemic started, 83% have occurred in sub-Saharan Africa (Gilks, 1999, p. 180). Among children under age 15 living with HIV/AIDS, 90% live in sub-Saharan Africa as do 95% of all AIDS orphans. In several of the 34 sub-Saharan nations, 1 out of every 4 adults is HIV-positive (UNAIDS, 1998, p. 1). Taxing low-income countries with health care systems inadequate to handle the burden of non-AIDS related illnesses, AIDS has devastated many of the sub-Saharan African economies. The impact of AIDS on the region is such that it is now affecting demographics changing mortality and fertility rates, reducing lifespan, and ultimately affecting population growth. Although Africa is the region of the world hardest hit by AIDS, and although no country has entirely escaped the virus, prevalence rates vary dramatically between regions, countries, and even within countries. In general, the southern region is the most affected, with Botswana, Namibia, Swaziland and Zimbabwe showing the highest rates, while West Africa has been less affected. In almost all countries, the HIV/AIDS prevalence rate is significantly higher in urban areas than in rural areas. Within the general population, the highest prevalence rates are found among the sexually active adult (15 to 49 years old) population. Women tend to get infected at earlier ages than males for a variety of biological and sociocultural reasons. In recent years an intensive government-sponsored HIV prevention campaign focusing on use of condoms and changes in sexual behavior has produced impressive results. Researchers however, have yet to satisfactorily explain the broad variation in HIV seroprevalence between Western and Eastern sub-Saharan Africa. As Gilks (1999) observes, â€Å"in some of the countries of Western Africa such as Senegal, low levels of HIV prevalence in adults have been maintained for about a decade, despite many circumstances highly conducive to appreciable and sustained transmission† (p. 181). In some Western African nations, early and sustained prevention programs may be responsible for the differences, although other reports indicate that comparatively low transmission rates prevail in most of the Western countries regardless of programs designed to encourage safer sex (UNAIDS, 1998, p. 2). Reports also show that differences in the rate of HIV spread between East and West Africa cannot be explai ned by differences in sexual behavior alone. AIDS researchers typically make a distinction between concentrated and generalized transmission patterns of the virus. In a concentrated transmission pattern, infection tends to be concentrated within â€Å"vulnerable groups† such as homosexual men, prostitutes, and IV drug users. In the generalized pattern, infection is diffused broadly through the population, typically by means of heterosexual transmission. In sub-Saharan Africa, where heterosexual transmission predominates, the pattern is that of generalized transmission. Compared to the U.S. little HIV transmission in Africa is related to IV drug use or unprotected homosexual sex. In addition to heterosexual transmission, transmission via transfusion and through contaminated medical equipment is not uncommon in sub-Saharan Africa. Africans infected with HIV die much sooner after diagnosis than HIV-infected persons in other parts of the world. Studies in industrialized countries that were conducted prior to the introduction of treatment with multiple antiretroviral drugs, found that the survival time following the diagnosis of AIDS ranged from 9 to 26 months. However, in Africa the survival time of patients with AIDS ranged from 5 to 9 months (Unaids, 1998, p.2). A number of factors have been cited to explain the shorter survival times in African which include lower access to health care, poorer quality of health care services, poorer levels of baseline health and nutrition, and greater exposure to pathogens likely to result in opportunistic infection and early death (UNAIDS, 1998; UNAIDS, 1999; Gilks, 1999). Mortality Life Expectancy. There is now compelling evidence drawn from two decades of AIDS epidemic data in central and east Africa that the AIDS epidemic has had a dramatic and negative impact upon mortality rates and life expectancy in this region. The most substantial increases in the mortality rate have occurred among adults aged 20 to 40 in the southern and eastern regions of sub-Saharan Africa, with more modest mortality rate increases shown for children within this region. The probability that a male adult in Zimbabwe would die between the ages of 15 and 60 jumped from 0.181 in 1979 to 0.325 in 1992, while the probability that a female adult would die between these ages during this time period jumped from 0.248 to 0.419 (Timaeus, 1998, p. S21). The increased mortality rates have had a substantial impact on life expectancies in the affected regions. A study in rural Uganda found that life expectancy dropped from just under 60 years to 42.5 years during the past two decades (Boerma, Nunn Whitworth, 1998). In late 1998, the UN Population Division released figures suggesting that AIDS has taken an average of seven years off the average life expectancy at birth of a baby born in any of the 29 most affected African countries. On average, in the absence of AIDS, life expectancy for these 29 countries would have averaged 54 yea rs; now, however, the average has dropped to 47 years. Fertility. A number of studies have now documented that HIV infection significantly reduces the fertility levels of HIV+ women in the sub-Saharan African countries. Studies on fertility changes in 20 sub-Saharan African countries found a 25% to 40% decline in fertility among HIV+ women versus their HIV-negative counterparts in the same country. Researchers note that HIV decreases fertility among HIV+ women as a consequence of both biological (impact on fecundity) and behavioral factors. On the biological level, there is an increase (among HIV+ women) in menstrual disorders, miscarriages, other STDs, and partner mortality all of which negatively impact fertility. On the behavioral level, HIV+ status may prompt increased divorce and separation, increased use of condoms and/or other barrier contraceptives, and reduced sexual frequency (Zaba Gregson, 1998; Gregson, et al., 1999). Biological and behavioral factors among HIV+ men ma y also impact the fertility rates. In general, researchers have noted that biological factors, including reduced sperm count and reduced frequency of sexual activity related to physical illness, have been more important than behavioral factors (condom use, etc.) when examining males’ contributions to the declining fertility rates (Zaba Gregson, 1998). Macbeth Novel Analysis EssayBIBLIOGRAPHYAltman, L.K. (1999a). More African women have AIDS than men. New York Times, 24 November 1999 Altman, L.K. (1999b). U.N. issues grim report on the 11 million children orphaned by AIDS. New York Times, 2 December 1999 Boerma, J.T.; Nunn, A.J.; Whitworth, J.A.G. (1998). Mortality impact of the AIDS epidemic: evidence from community studies in less developed countries. AIDS, 12 (Suppl. 1), S1-S14. Boyle, B. (1998). The global impact of HIV Bridging ever widening gap. Coverage from the 12th World AIDS Conference, June 29 July 2, 1998. Gilks, C.F. (1999). The challenge of HIV/AIDS in Sub-Saharan Africa. Journal of the Royal College of Physicians of London, 33 (2), 180-185. Gregson, S.; Zaba, B.; Garnett, G.P. (1999). Low fertility in women with HIV and the impact of the epidemic on orphanhood and early childhood mortality in sub-Saharan Africa. AIDS, 13 (Suppl. A), S249-S257. Ibrahim, Y.M. (1998). AIDS is slashing Africa’s population, U.N. survey finds. New York Times, 28 October 1998Reuters Health (1999a). Economic empowerment of women key to halting AIDS epidemic in Africa. Reuters Medical News, 14 October 1999 Reuters Health (1999b). HIV/AIDS devastating economies in Sub-Saharan Africa. Reuters Medical News, 13 October 1999 Timaeus, I.M. (1998). Impact of the HIV epidemic on mortality in sub-Saharan Africa: evidence from national surveys and consensus. AIDS, 12 (Suppl. D), S15-S27. UNAIDS (1998). AIDS in Africa. UNAIDS Fact Sheet (30 November 1998) UNAIDS (1999). Differences in HIV spread in four sub-Saharan African cities. UNAIDS Fact Sheet (14 September 1999) Sociology Essays