Hot answers tagged chromosome
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Note that anyone with a Y chromosome is considered a genetic male. Also, aneuploidy is usually a result of nondisjunction (but can have other causes as well) and is usually not inherited.
47,XXX is called Triple X syndrome and occurs in approximately 1 in 1,000 female births. These individuals usually appear normal, but may have tall stature, a small head, ...
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Great question, and one about which there has historically been a lot of speculation, and there is currently a lot of misinformation. I will first address the two answers given by other users, which are both incorrect but have been historically suggested by scientists. Then I will try to explain the current understanding (which is not simple or complete). My ...
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No, an external physical examination would be inconclusive. The reason is the TDF
gene. To be more specific, if a person has XY and the gene is not active then the subject
would have a female appearance. Also we cannot conclude that a person has a Y
chromosome even if it has penis because that gene could be transferred on the X chromosome.
Here is a ...
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Each chromosome is a distinct, separate DNA molecule. A chromosome of an eukariotic cell nucleus is a (long) linear molecule and so has two ends, which are called telomeres. DNA naturally forms double helix, and the molecules can further curl in what are called supercoils.
In humans, the chromosomes occur in 23 pairs (totaling 46). Except for the sex ...
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I think it is the wrong question. You assume that eukaryotes developed from a single-cell organism with circular DNA. Then, clearly, there must have been an advantage of (newly) developing a linear genome. But eukaryotes could have developed from an organism with linear DNA, too. There are still a few bacterial species with linear chromosomes, so this is not ...
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@nico is right. the number of chromosomes is the result of an evolutionary timeline, puncutated by sometimes spontaneous events which shape the DNA.
These events occur in the course of evolution:
1) Chromosomal rearrangements. Large sections of the genome can flip around or become integrated in other chromosomes. By homologous recombination, regions of ...
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Here is a paper you might want to take a look at:
Phylogenetic Origin of Human Chromosomes 7, 16, and 19 and their Homologs in Placental Mammals
From the abstract:
From their origin, these chromosomes underwent the following rearrangements to give rise to current human chromosomes: centromeric fission of the two submetacentrics in ancestors of all ...
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Plants have a simpler anatomical structure than mammals (is anatomical the right word, or would physiological be more appropriate?). Mammals on average don't have more genes than plants, so my understanding is that this additional complexity is the result of finer and more complex regulatory mechanisms.
When you remove or duplicate an individual gene in an ...
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Answer
An comprehensive online database of the chromosome numbers of all living species most likely doesn't exist. This Wikipedia article is the best and most complete reference comprising animals that I can personally find on the internet.
This source in Spanish, which I've translated with Google Translate reads:
Canedo Delgado (1999) performed the ...
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I would say this is a question that might not be resolved yet.
Going back to the earliest days of DNA - a billion years ago - its hard to imagine circular DNA being the first sort to show up. Its speculated that in the transition from RNA world to DNA world, early on each gene had a separate piece of nucleic acid coding for it which would not have been ...
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It is hard to give an answer to this question that is not just speculation. We can be reasonably confident that the most recent common ancestor of bacteria and archaea had circular genomes. However, we currently have no way to get any conclusive evidence earlier than that. 3 billion year old DNA doesn't fossilize. So it's just speculation what DNA looked ...
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This question appears to start from the premise that different species of yeast are closely related, but they aren't. Saccharomyces cerevisae and Schizosaccharomyces pombe, both Ascomycetes, are thought to have diverged at least 300 million years ago (c.f. the mammalian divergence from other vertebrates was about 200 million years ago).
S. cerevisiae has a ...
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You can package linear genomes much more efficiently than circular genomes, and bacteria simply don't require the information density to be prosperous.
To be a bit more specific, it's the torque strain put on the double-helix while it's being wound that makes the difference. Linear genomes can be wound around Histones, and these Histones can be further ...
3
Since you didn't specify animals, I will add here for anyone coming from google that plant chromosome numbers are stored in the Index to Plant Chromosome Numbers.
I would be surprised if such a database exists for animals (except maybe insects) as historically C-numbers of plants and other cytogenetics were important for taxonomy (and still is important), ...
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So the DNA in some chromosomes must have the pieces of information about how to do the DNA replication. - I am not sure about thing.
Genomes contain what is called the "origin of replication" - specific sequences in the DNA that tell DNA polymerase where to bind and to initiate replication.
As for your main question, I'm a little confused as to what ...
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I think the OP is asking why we have one less chromosome pair than chimpanzees (for example) [23 pairs instead of 24].
The is an abundance of evidence, as alluded to above by shigeta, that human chromosome 2 is the result of a telomere-to-telomere fusion of two ancestral chromosomes (IJdo et al., 1991). This event did not occur in our closest ancestors, ...
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An interesting condition is androgen insentivity syndrome. In AIS, the body is unable to respond to androgens, the male sex hormone, of which testosterone is the best known. The most common cause is a defective androgen receptor, and most of these diseases are X-linked. In extreme cases, complete androgen insensitivy syndrome (CAIS) can occur. Genetic males ...
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This link seems to have good information that answers most of your questions.
In my mind, there are two types of mitochondria: ones that work and ones that don't. Mitochondria do have DNA but that mDNA is there to encode proteins for their specific functions (e.g. to create ATP). So, although the mDNA may not be uniform for every mitochondrion in your body, ...
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As @dd3 points out, average GC% indicates a need for stability and coding regions or structural regions of the genome may need to be more stable. But the largest %GC in genomes are found in thermophiles - organisms which live in high temperature water - in hotsprings and undersea geothermal vents. This review mentions how some thermophiles can be found with ...
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Trisomy is due to non-disjunction in meiosis (the process in which eggs and sperm are created). This happens before fertilization.
Trisomies are more frequently seen in children of older women. It's not fully understood why this happens, but it is likely related to the fact that the oocytes do not complete meiosis (and become eggs) until ovulation. Here's ...
2
Although crossover events can be observed in mitosis (mitotic recombination), they most frequently occur in prophase I of meiosis (crossing over in bivalents). Circular chromosomes are common in prokaryotes, but eukaryotes have linear chromosomes. Remember what meiosis accomplishes and that prokaryotes reproduce asexually. Prokaryotes don't have a need for ...
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Since it sounds like you are the one designing the database, you can make this a number of ways. The simplest is probably to reduce it to two variables, likely two decimals.
See this hemoglobin example for a chromosomal locus example.
There are N chromosomes (23 for humans, if you like, sex chromosomes can be treated as a pair).
There are 2 chromatids per ...
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In animals, polyploidy is not tolerated and very few polyploid species
are known to exist. Those that do exist are usually asexual,
parthenogenetic, or hermaphroditic. Most of the problems resulting
from polyploidy occur during synapsis of homologues during prophase I.
As plants do not have a chromosomal mechanism for sex determination,
...
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Regarding the Papers referenced above:
If the authors maintain that the evidence at the site of fusion is not clear and that explanations as to how this happened are flawed that is possibly concedable. They would need to do more homework than these papers. The discussion of vestigial centromere sequences and telomere motifs being inverted is ...
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It turns out that this was a question that was answered by Alan Turing in the 1950s.
Turing hypothesized there would be two morphogens, an inhibitor/ activator pair, each of which would produce a one of two phenotypes by activation or suppression of a trait. He hypothesized that this would produce a pattern like stripes or other patterns (e.g. black and ...
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SRY translocation to the X chromosome clinically exists and characterizes the De La Chapelle Syndrome. The phenotype associated to this syndrome demonstrates the necessity of other components on the Y chromosome to develop full masculine characteristics.
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There is significant variation in genomic GC content, both between species and within an individual genome. An average GC content in the range of 35%-45% is common, although there are definitely organisms that fall outside this range. The plasmodium species you link to above is an example of extreme AT richness (low GC content), whereas some bacterial ...
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Starting out with RNA data is great, since you already have fully spliced entities, despite being in a different dynamic regime.
As the chromatin landscape itself is dynamic and High throughput data exploration has only begun in the last decade, consider the following tools and results with care...
You may find the following tools helpful:
Archalign , ...
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I asked my professor, and the answer appears to be differences in both the generation and the final product.
Free chromosome fragments are created through irradiation/other damage of the germline in one animal. Through a series of crosses, it is possible to introduce individual fragments (containing a duplication of your gene of interest, as well as a ...
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To begin, one might ask "What is the advantage of higher GC content?"
Higher GC content is associated with higher stability of the DNA, and accordingly, people have suggested that this is important for protein-coding regions. It has been found that there are quite a few protein-coding regions in GC-rich regions, but I am not sure whether the converse is ...
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