tugas bio ku
• Penyebab klinefelter
Pada kondisi normal manusia memiliki 46 kromosom, terdiri dari 44 kromosom tubuh dan 2 kromosom seks. Kromosom seks ini akan menentukan apakah anda laki-laki atau perempuan. Normalnya laki-laki memiliki kromosom seks berupa XY sedangkan wanita XX. Pada proses pembentukan gamet terjadi reduksi jumlah kromosom yang mulanya berjumlah 46 menjadi 23. Pada tahap tersebut juga terjadi pemisahan kromosom seks, misalnya pada pria XY berpisah menjadi X dan Y begitupun dengan wanita XX menjadi X dan X. Jika terjadi pembuahan pria maupun wanita akan menyumbangkan satu kromosom seksnya begitupun dengan kromosom tubuhnya sehingga terbentuk individu baru dengan 46 kromosom.
Pada sindrom klinefelter terjadi gagal pisah pada pria dan atau wanita. Jika yang gagal berpisah adalah kromosom seks dari pria maka gamet yang ia sumbangkan memiliki kromosom seks XY yang nantinya akan menyatu dengan kromosom X dari wanita dalam proses pembuahan sehingga yang terjadi adalah bentuk abnormal 47,XXY (bentuk ini adalah bentuk yang umumnya terjadi pada sindrom klinefelter). Ataupun bila wanita menyumbangkan XX dan pria menyumbangkan Y. Atau bentuk lain yang terjadi akibat pria menyumbangkan XY dan wanita menyumbangkan XX sehingga yang terjadi adalah sindrom klinefelter berbentuk 48,XXXY.
Selain dapat terjadi akibat gagal berpisah pada saat pembentukan gamet, sindrom klinefelter juga dapat disebabkan oleh gagal berpisah pada tahap mitosis setelah terjadinya pembuahan membentuk mosaik klinefelter 46,XY/47,XXY. Biasanya bentuk gejala klinis pada bentuk mosaik ini lebih ringan daripada bentuk klasiknya tetapi hal ini tergantung dari sebanyak apa mosaiknya.
Sindrom Down adalah suatu kumpulan gejala akibat dari abnormalitas kromosom, biasanya kromosom 21, yang tidak berhasil memisahkan diri selama meiosis sehingga terjadi individu dengan 47 kromosom. Sindrom ini pertama kali diuraikan oleh Langdon Down pada tahun 1866.
Down Syndrom merupakan kelainan kromosom autosomal yang paling banyak terjadi pada manusia. Diperkirakan 20 % anak dengan down syndrom dilahirkan oleh ibu yang berusia diatas 35 tahun. Synrom down merupakan cacat bawaan yang disebabkan oleh adanya kelebiha kromosom x. Syndrom ini juga disebut Trisomy 21, karena 3 dari 21 kromosom menggantikan yang normal.95 % kasus syndrom down disebabkan oleh kelebihan kromosom.
Causes
Most cases of Patau's syndrome result from trisomy 13, which means each cell in the body has three copies of chromosome 13 instead of the usual two copies. A small percentage of cases occur when only some of the body's cells have an extra copy, resulting in a mixed population of cells with a differing number of chromosomes; such cases are called mosaic Patau.
Patau syndrome can also occur when part of chromosome 13 becomes attached to another chromosome (translocated) before or at conception. Affected people have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 13 and often the physical signs of the syndrome differ from the typical Patau syndrome.
Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called non-disjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of the chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each of the body's cells. Mosaic Patau syndrome is also not inherited. It occurs as a random error during cell division early in fetal development.
Patau syndrome due to a translocation can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 13. Although they do not have signs of Patau syndrome, people who carry this type of balanced translocation are at an increased risk of having children with the condition.
Apakah sindroma down itu?
Pada tahun 1866, Dokter John Langdon Down, mendeskripsikan dengan tepat seorang penyandang sindroma down dan menjadikannya "Bapak" Sindroma Down. Pada tahun 1959, Dokter Jerome Lejeune mengidentifikasikan sindroma down sebagai keabnormalan/kelainan kromosome. Dokter Lejeune tidak menemukan 46 kromosome pada penyandang Sindroma Down melainkan 47 kromosome. Kelebihan kromosome inilah yang menimbulkan ciri khas sindroma down. Kelebihan kromosome ini terjadi pada kromosome yang ke-21 dan kerena 95% kasus sindroma down disebabkan karena adanya 3 copy kromosome 21, maka sering juga disebut Trisomy 21. Dapat juga terjadi kelainan pada pembelahan sel ditubuhnya, dimana tidak semua sel mengandung kelainan pada kromosome 21nya, sehingga terdapat 3 jenis sindroma down sebagai berikut
1. Trisomi-21 (semua gene mengalami perubahan) 95%
2. Translocation (bawaan) 4%
3. Mosaic (tidak semua gene yang mengalami perubahan karena extra kromosom) 1%
Apa penyebab sindroma down?
sindroma down terjadi karena kelainan pembelahan sel di seluruh tubuhnya yang disebut "non disjunction". Hal ini menghasilkan embrio (janin) dengan 3 copy kromosome, bukan 2 copy sebagaimana normalnya. Hingga kini penyebab "non disjunction" belum diketahui.
80% penyandang sindroma down dilahirkan oleh ibu-ibu muda usia. Jadi faktor usia bukan suatu penyebab utama sindroma ini.
Sindroma Jacob (SJ) merupakan kelainan kromosom laki2 yang jarang ditemukan. Pada sindroma ini, kromosom laki-laki normal yang biasanya X dan Y (46 XY) mendapat tambahan kromosom Y sehingga menjadi XYY (47 XYY). Laki-laki dengan SJ disebut dengan istilah laki-laki XYY.
Penyebab pastinya masih belum diketahui. Diduga terjadi kesalahan dalam pemisahan kromosom di tahap anafase II yang dinamakan nondisjunction yang mengakibatkan sel sperma memiliki kelebihan kromosom Y. Jika kemudian sperma ini membuahi sel telur maka terjadilah SJ.
What fun questions! Despite its name, X inactivation is really fascinating. It is why, for example, Calico cats look the way they do. Or why some women have patches of skin lacking sweat glands!
Before answering your questions, let's go into a bit of detail about X inactivation. If you don't need the intro, you can skip ahead 10 paragraphs or so to get directly to the answers.
Normally, men have one X chromosome and women have two. X inactivation is the process where one of a woman's X chromosomes gets shut off.
This process makes it so that both men and women have one working X chromosome. The reason this happens has to do with genes.
Remember, genes are just recipes for proteins. They tell the body what and how much of a protein to make.
And it is the how much that is important for X inactivation. If there were no X inactivation, women would make twice as much of all 1100 or so proteins encoded by X chromosome genes.
For some genes, this isn't a big deal. For example, some of us have blue eyes because the gene for eye color is broken (click here for more details). A broken gene is the same as one that isn't there.
So, people with brown or green eyes have more working copies of eye color genes than people with blue eyes. No harm in that. But not every case of an extra gene is so benign.
An example where extra copies of genes can be a problem is Down syndrome. Down syndrome happens when someone has an extra chromosome 21. The symptoms arise from the extra protein made from the additional copies of the 225 genes on this chromosome.
Actually, not all 225 genes are involved. There are some people with Down syndrome who only have an extra piece of chromosome 21. By looking at many of these patients, scientists have narrowed the region that causes Down syndrome to 33 genes. In other words, when your body makes more protein from these extra 33 genes, you end up having Down syndrome.
Chromosome 21 is one of the few chromosomes where you can live for long with three of them. Most of the others result in severe problems or, usually, death. So we wouldn't be able to tolerate the extra 1100 genes of the X chromosome.
Given how we mammals decide whether to be a boy or a girl, we needed to come up with a way to shut off one of the X chromosomes in females (click here to see how other animals determine gender). What biology came up with was X inactivation.
Very early on, probably when women are only 32 cells big, an X chromosome shuts off randomly in each cell. In other words, it isn't always the same X chromosome that gets shut off in each of these 32 cells.
Each of these cells then gives rise to billions and billions of other cells. So women have swaths of cells that have one X turned on and other patches with a different X on. This is called being a mosaic.
The classic mosaic example is Calico cats. One of the genes for hair color is found on the X chromosome. The gene makes either orange or black (white is on a different chromosome).
Each colored patch on a calico has a different X turned on. If the patch is orange, then there are a bunch of cells there with the orange X on. A black patch has a bunch of cells with the black patch on.
This is why a male calico is so rare. Most males only have a single X and so either the orange or the black hair color gene, not both.
We talked earlier about how having extra chromosomes is usually lethal. One of the exceptions to this rule is the X chromosome.
This makes sense if extra X's get shut off anyway. And yet, there are health consequences for people who are missing an X or have extra copies of the X chromosome.
An example of this is what you were asking about, Klinefelter's syndrome. A person with Klinefelter's syndrome has a Y chromosome and more than one X chromosome.
If X inactivation were complete, this shouldn't be a problem—these folks should be normal males. And yet, as the fact that they have a syndrome implies, they have health problems. Why is this?
First off, only one of their X chromosomes is active. Having the Y chromosome doesn't seem to affect X inactivation itself.
The problem comes from the fact that X inactivation is not complete. X inactivation starts at the middle of the chromosome and spreads towards the ends. Apparently it peters out before it makes it all the way.
The genes at the ends that are still on lead to Klinefelter's syndrome. In fact, many of the symptoms of Klinefelter's are really those of a feminized male.
But the incomplete X inactivation is OK for women—these genes are supposed to be double expressed in females. The petering out process doesn't stop at the same place for each woman. So some women have different genes turned on at different levels. Scientists are exploring what having more or less of these extra genes might mean for women.
As you can tell, the extra X chromosome in Klinefelter's is already inactivated. To "cure" Klinefelter's, scientists would need to learn completely shut off the extra X chromosomes very early on without affecting the active X. A pretty tall order that isn't likely to happen anytime soon.
Pada kondisi normal manusia memiliki 46 kromosom, terdiri dari 44 kromosom tubuh dan 2 kromosom seks. Kromosom seks ini akan menentukan apakah anda laki-laki atau perempuan. Normalnya laki-laki memiliki kromosom seks berupa XY sedangkan wanita XX. Pada proses pembentukan gamet terjadi reduksi jumlah kromosom yang mulanya berjumlah 46 menjadi 23. Pada tahap tersebut juga terjadi pemisahan kromosom seks, misalnya pada pria XY berpisah menjadi X dan Y begitupun dengan wanita XX menjadi X dan X. Jika terjadi pembuahan pria maupun wanita akan menyumbangkan satu kromosom seksnya begitupun dengan kromosom tubuhnya sehingga terbentuk individu baru dengan 46 kromosom.
Pada sindrom klinefelter terjadi gagal pisah pada pria dan atau wanita. Jika yang gagal berpisah adalah kromosom seks dari pria maka gamet yang ia sumbangkan memiliki kromosom seks XY yang nantinya akan menyatu dengan kromosom X dari wanita dalam proses pembuahan sehingga yang terjadi adalah bentuk abnormal 47,XXY (bentuk ini adalah bentuk yang umumnya terjadi pada sindrom klinefelter). Ataupun bila wanita menyumbangkan XX dan pria menyumbangkan Y. Atau bentuk lain yang terjadi akibat pria menyumbangkan XY dan wanita menyumbangkan XX sehingga yang terjadi adalah sindrom klinefelter berbentuk 48,XXXY.
Selain dapat terjadi akibat gagal berpisah pada saat pembentukan gamet, sindrom klinefelter juga dapat disebabkan oleh gagal berpisah pada tahap mitosis setelah terjadinya pembuahan membentuk mosaik klinefelter 46,XY/47,XXY. Biasanya bentuk gejala klinis pada bentuk mosaik ini lebih ringan daripada bentuk klasiknya tetapi hal ini tergantung dari sebanyak apa mosaiknya.
Sindrom Down adalah suatu kumpulan gejala akibat dari abnormalitas kromosom, biasanya kromosom 21, yang tidak berhasil memisahkan diri selama meiosis sehingga terjadi individu dengan 47 kromosom. Sindrom ini pertama kali diuraikan oleh Langdon Down pada tahun 1866.
Down Syndrom merupakan kelainan kromosom autosomal yang paling banyak terjadi pada manusia. Diperkirakan 20 % anak dengan down syndrom dilahirkan oleh ibu yang berusia diatas 35 tahun. Synrom down merupakan cacat bawaan yang disebabkan oleh adanya kelebiha kromosom x. Syndrom ini juga disebut Trisomy 21, karena 3 dari 21 kromosom menggantikan yang normal.95 % kasus syndrom down disebabkan oleh kelebihan kromosom.
Causes
Most cases of Patau's syndrome result from trisomy 13, which means each cell in the body has three copies of chromosome 13 instead of the usual two copies. A small percentage of cases occur when only some of the body's cells have an extra copy, resulting in a mixed population of cells with a differing number of chromosomes; such cases are called mosaic Patau.
Patau syndrome can also occur when part of chromosome 13 becomes attached to another chromosome (translocated) before or at conception. Affected people have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 13 and often the physical signs of the syndrome differ from the typical Patau syndrome.
Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called non-disjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of the chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each of the body's cells. Mosaic Patau syndrome is also not inherited. It occurs as a random error during cell division early in fetal development.
Patau syndrome due to a translocation can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 13. Although they do not have signs of Patau syndrome, people who carry this type of balanced translocation are at an increased risk of having children with the condition.
Apakah sindroma down itu?
Pada tahun 1866, Dokter John Langdon Down, mendeskripsikan dengan tepat seorang penyandang sindroma down dan menjadikannya "Bapak" Sindroma Down. Pada tahun 1959, Dokter Jerome Lejeune mengidentifikasikan sindroma down sebagai keabnormalan/kelainan kromosome. Dokter Lejeune tidak menemukan 46 kromosome pada penyandang Sindroma Down melainkan 47 kromosome. Kelebihan kromosome inilah yang menimbulkan ciri khas sindroma down. Kelebihan kromosome ini terjadi pada kromosome yang ke-21 dan kerena 95% kasus sindroma down disebabkan karena adanya 3 copy kromosome 21, maka sering juga disebut Trisomy 21. Dapat juga terjadi kelainan pada pembelahan sel ditubuhnya, dimana tidak semua sel mengandung kelainan pada kromosome 21nya, sehingga terdapat 3 jenis sindroma down sebagai berikut
1. Trisomi-21 (semua gene mengalami perubahan) 95%
2. Translocation (bawaan) 4%
3. Mosaic (tidak semua gene yang mengalami perubahan karena extra kromosom) 1%
Apa penyebab sindroma down?
sindroma down terjadi karena kelainan pembelahan sel di seluruh tubuhnya yang disebut "non disjunction". Hal ini menghasilkan embrio (janin) dengan 3 copy kromosome, bukan 2 copy sebagaimana normalnya. Hingga kini penyebab "non disjunction" belum diketahui.
80% penyandang sindroma down dilahirkan oleh ibu-ibu muda usia. Jadi faktor usia bukan suatu penyebab utama sindroma ini.
Sindroma Jacob (SJ) merupakan kelainan kromosom laki2 yang jarang ditemukan. Pada sindroma ini, kromosom laki-laki normal yang biasanya X dan Y (46 XY) mendapat tambahan kromosom Y sehingga menjadi XYY (47 XYY). Laki-laki dengan SJ disebut dengan istilah laki-laki XYY.
Penyebab pastinya masih belum diketahui. Diduga terjadi kesalahan dalam pemisahan kromosom di tahap anafase II yang dinamakan nondisjunction yang mengakibatkan sel sperma memiliki kelebihan kromosom Y. Jika kemudian sperma ini membuahi sel telur maka terjadilah SJ.
What fun questions! Despite its name, X inactivation is really fascinating. It is why, for example, Calico cats look the way they do. Or why some women have patches of skin lacking sweat glands!
Before answering your questions, let's go into a bit of detail about X inactivation. If you don't need the intro, you can skip ahead 10 paragraphs or so to get directly to the answers.
Normally, men have one X chromosome and women have two. X inactivation is the process where one of a woman's X chromosomes gets shut off.
This process makes it so that both men and women have one working X chromosome. The reason this happens has to do with genes.
Remember, genes are just recipes for proteins. They tell the body what and how much of a protein to make.
And it is the how much that is important for X inactivation. If there were no X inactivation, women would make twice as much of all 1100 or so proteins encoded by X chromosome genes.
For some genes, this isn't a big deal. For example, some of us have blue eyes because the gene for eye color is broken (click here for more details). A broken gene is the same as one that isn't there.
So, people with brown or green eyes have more working copies of eye color genes than people with blue eyes. No harm in that. But not every case of an extra gene is so benign.
An example where extra copies of genes can be a problem is Down syndrome. Down syndrome happens when someone has an extra chromosome 21. The symptoms arise from the extra protein made from the additional copies of the 225 genes on this chromosome.
Actually, not all 225 genes are involved. There are some people with Down syndrome who only have an extra piece of chromosome 21. By looking at many of these patients, scientists have narrowed the region that causes Down syndrome to 33 genes. In other words, when your body makes more protein from these extra 33 genes, you end up having Down syndrome.
Chromosome 21 is one of the few chromosomes where you can live for long with three of them. Most of the others result in severe problems or, usually, death. So we wouldn't be able to tolerate the extra 1100 genes of the X chromosome.
Given how we mammals decide whether to be a boy or a girl, we needed to come up with a way to shut off one of the X chromosomes in females (click here to see how other animals determine gender). What biology came up with was X inactivation.
Very early on, probably when women are only 32 cells big, an X chromosome shuts off randomly in each cell. In other words, it isn't always the same X chromosome that gets shut off in each of these 32 cells.
Each of these cells then gives rise to billions and billions of other cells. So women have swaths of cells that have one X turned on and other patches with a different X on. This is called being a mosaic.
The classic mosaic example is Calico cats. One of the genes for hair color is found on the X chromosome. The gene makes either orange or black (white is on a different chromosome).
Each colored patch on a calico has a different X turned on. If the patch is orange, then there are a bunch of cells there with the orange X on. A black patch has a bunch of cells with the black patch on.
This is why a male calico is so rare. Most males only have a single X and so either the orange or the black hair color gene, not both.
We talked earlier about how having extra chromosomes is usually lethal. One of the exceptions to this rule is the X chromosome.
This makes sense if extra X's get shut off anyway. And yet, there are health consequences for people who are missing an X or have extra copies of the X chromosome.
An example of this is what you were asking about, Klinefelter's syndrome. A person with Klinefelter's syndrome has a Y chromosome and more than one X chromosome.
If X inactivation were complete, this shouldn't be a problem—these folks should be normal males. And yet, as the fact that they have a syndrome implies, they have health problems. Why is this?
First off, only one of their X chromosomes is active. Having the Y chromosome doesn't seem to affect X inactivation itself.
The problem comes from the fact that X inactivation is not complete. X inactivation starts at the middle of the chromosome and spreads towards the ends. Apparently it peters out before it makes it all the way.
The genes at the ends that are still on lead to Klinefelter's syndrome. In fact, many of the symptoms of Klinefelter's are really those of a feminized male.
But the incomplete X inactivation is OK for women—these genes are supposed to be double expressed in females. The petering out process doesn't stop at the same place for each woman. So some women have different genes turned on at different levels. Scientists are exploring what having more or less of these extra genes might mean for women.
As you can tell, the extra X chromosome in Klinefelter's is already inactivated. To "cure" Klinefelter's, scientists would need to learn completely shut off the extra X chromosomes very early on without affecting the active X. A pretty tall order that isn't likely to happen anytime soon.
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