Saturday, January 5, 2008

Best LCD and Plasma TV's for Standard Definition

While there is nothing to compare with the pristine quality of High Definition pictures on your LCD or Plasma TV, the fact is that for most of us the majority of our viewing schedule will still be Standard Definition (SD) quality.

Having seen a HD demonstration at their local electrical outlet, many consumers have been disappointed when the same TV displays SD pictures.

While the choice of TV is a very subjective and personal choice, we can make some observations on SD/HD pictures and offer some suggestions for TV's that in our opinion perform well with SD material.

We have to point out that here at HDTVorg we are Plasma fans when it comes to SD pictures. We like the 'softer' pictures a Plasma produces, although we realise that there are many of you out there who simply prefer LCD, and there are in fact a few LCD TV's that have made it into our top ten that fully deserve to be there.

We strongly recommend that you compare as many LCD / Plasma TV's alongside each other with SD and HD material on screen. Any retailer worth their salt will go out of their way to help. Also remember;

(i) Viewing distances usually differ with SD and HD for the same screen. HD will invariably be better viewed close, while moving away from the screen will produce better results for SD.

(ii) Generally, but not always, smaller screens make for better SD viewing, and Full HD (1920 x 1080) screens sometimes struggle to handle an SD source because more upsacling is required for a lower quality SD source to 'fit' the extra resolution.

(iii) Ultimately, the picture processing technology employed on a TV will be the single most important factor which determines how good the SD and HD picture is - again, we would like to stress how important it is to compare as many TV's as you can with SD and HD material.

Laser TV set to star at CES 2008

With the invitations already sent out, the Japanese conglomerate Mitsubishi plans to unveil its take on laser TV at the forthcoming Consumer Electronics Show (CES) in Las Vegas.

At half the weight, and using quarter of the electricity of conventional plasma and LCD TVs there is understandably much interest in the laser TV's.

With the technology's ability to increase the screens colour content from 30-35% of what the eye can see to 90%, laser screens have certainly wetted the appetite.

Whether or not Mitsubishi will unveil something significant, which has the potential for commercial launch, remains to be seen. Along with a growing number of industry insiders we have become more and more skeptical about revolutionary new screen technologies.

It is not so much that the new technologies don't work, in fact demonstrations of SED and OLED based screens for example have been quite jaw dropping. Having developed a growing feeling that these technologies have been demonstrated for marketing purposes however, it is the potential that they have for a commercial launch in the foreseeable future that will now make really sit up and take notice.

Chromosome abnormalities

The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two chromosome mutations; insertion (1) and translocation (2).
The two major two chromosome mutations; insertion (1) and translocation (2).

A chromosome abnormality reflects an abnormality of chromosome number or structure. Chromosome abnormalities usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome abnormalities. They can be organized into two basic groups, numerical and structural abnormalities.

Numerical abnormalities

When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Turner Syndrome is an example of a monosomy where the individual is born with only one sex chromosome, an X.

Structural abnormalities

When the chromosome's structure is altered. This can take several forms:

  • Deletions: A portion of the chromosome is missing or deleted. Known disorders include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.
  • Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material. Known disorders include Charcot-Marie-Tooth disease type 1A which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
  • Translocations: When a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere; these only occur with chromosomes 13, 14, 15, 21 and 22.
  • Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
  • Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
  • Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.

Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.


Most chromosome abnormalities occur as an accident in the egg or sperm, and are therefore not inherited. Therefore, the abnormality is present in every cell of the body. Some abnormalities, however, can happen after conception, resulting in mosaicism (where some cells have the abnormality and some do not). Chromosome abnormalities can be inherited from a parent or be "de novo". This is why chromosome studies are often performed on parents when a child is found to have an abnormality.

Human chromosomes

Human cells have 23 pairs of large linear nuclear chromosomes, giving a total of 46 per cell. In addition to these, human cells have many hundreds of copies of the mitochondrial genome. Sequencing of the human genome has provided a great deal of information about each of the chromosomes. Below is a table compiling statistics for the chromosomes, based on the Sanger Institute's human genome information in the Vertebrate Genome Annotation (VEGA) database.[28] Number of genes is an estimate as it is in part based on gene predictions. Total chromosome length is an estimate as well, based on the estimated size of unsequenced heterochromatin regions.

Chromosome Genes Total bases Sequenced bases[29]
1 3,148 247,200,000 224,999,719
2 902 242,750,000 237,712,649
3 1,436 199,450,000 194,704,827
4 453 191,260,000 187,297,063
5 609 180,840,000 177,702,766
6 1,585 170,900,000 167,273,992
7 1,824 158,820,000 154,952,424
8 781 146,270,000 142,612,826
9 1,229 140,440,000 120,312,298
10 1,312 135,370,000 131,624,737
11 405 134,450,000 131,130,853
12 1,330 132,290,000 130,303,534
13 623 114,130,000 95,559,980
14 886 106,360,000 88,290,585
15 676 100,340,000 81,341,915
16 898 88,820,000 78,884,754
17 1,367 78,650,000 77,800,220
18 365 76,120,000 74,656,155
19 1,553 63,810,000 55,785,651
20 816 62,440,000 59,505,254
21 446 46,940,000 34,171,998
22 595 49,530,000 34,893,953
X (sex chromosome) 1,093 154,910,000 151,058,754
Y (sex chromosome) 125 57,740,000 22,429,293

Chromosomal aberrations

The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two-chromosome mutations; insertion (1) and translocation (2).
The two major two-chromosome mutations; insertion (1) and translocation (2).
In Down syndrome, there are three copies of chromosome 21
In Down syndrome, there are three copies of chromosome 21

Chromosomal aberrations are disruptions in the normal chromosomal content of a cell, and are a major cause of genetic conditions in humans, such as Down syndrome. Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although they may lead to a higher chance of having a child with a chromosome disorder. Abnormal numbers of chromosomes or chromosome sets, aneuploidy, may be lethal or give rise to genetic disorders. Genetic counseling is offered for families that may carry a chromosome rearrangement.

The gain or loss of chromosome material can lead to a variety of genetic disorders. Human examples include:

  • Cri du chat, which is caused by the deletion of part of the short arm of chromosome 5. "Cri du chat" means "cry of the cat" in French, and the condition was so-named because affected babies make high-pitched cries that sound like a cat. Affected individuals have wide-set eyes, a small head and jaw and are moderately to severely mentally retarded and very short.
  • Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4. It is characterized by severe growth retardation and severe to profound mental retardation.
  • Down's syndrome, usually is caused by an extra copy of chromosome 21 (trisomy 21). Characteristics include decreased muscle tone, asymmetrical skull, slanting eyes and mild to moderate mental retardation.
  • Edwards syndrome, which is the second most common trisomy after Down syndrome. It is a trisomy of chromosome 18. Symptoms include mental and motor retardation and numerous congenital anomalies causing serious health problems. Ninety percent die in infancy; however, those who live past their first birthday usually are quite healthy thereafter. They have a characteristic hand appearance with clenched hands and overlapping fingers.
  • Patau Syndrome, also called D-Syndrome or trisomy-13. Symptoms are somewhat similar to those of trisomy-18, but they do not have the characteristic hand shape.
  • Idic15, abbreviation for Isodicentric 15 on chromosome 15; also called the following names due to various researches, but they all mean the same; IDIC(15), Inverted dupliction 15, extra Marker, Inv dup 15, partial tetrasomy 15
  • Jacobsen syndrome, also called the terminal 11q deletion disorder.[1] This is a very rare disorder. Those affected have normal intelligence or mild mental retardation, with poor expressive language skills. Most have a bleeding disorder called Paris-Trousseau syndrome.
  • Klinefelter's syndrome (XXY). Men with Klinefelter syndrome are usually sterile, and tend to have longer arms and legs and to be taller than their peers. Boys with the syndrome are often shy and quiet, and have a higher incidence of speech delay and dyslexia. During puberty, without testosterone treatment, some of them may develop gynecomastia.
  • Turner syndrome (X instead of XX or XY). In Turner syndrome, female sexual characteristics are present but underdeveloped. People with Turner syndrome often have a short stature, low hairline, abnormal eye features and bone development and a "caved-in" appearance to the chest.
  • XYY syndrome. XYY boys are usually taller than their siblings. Like XXY boys and XXX girls, they are somewhat more likely to have learning difficulties.
  • Triple-X syndrome (XXX). XXX girls tend to be tall and thin. They have a higher incidence of dyslexia.
  • Small supernumerary marker chromosome. This means there is an extra, abnormal chromosome. Features depend on the origin of the extra genetic material. Cat-eye syndrome and isodicentric chromosome 15 syndrome (or Idic15) are both caused by a supernumerary marker chromosome, as is Pallister-Killian syndrome.

Chromosomal mutations produce changes in whole chromosomes (more than one gene) or in the number of chromosomes present.

  • Deletion - loss of part of a chromosome
  • Duplication - extra copies of a part of a chromosome
  • Inversion - reverse the direction of a part of a chromosome
  • Translocation - part of a chromosome breaks off and attaches to another chromosome

Most mutations are neutral - have little or no effect

A detailed graphical display of all human chromosomes and the diseases annotated at the correct spot may be found at [2].

Number of chromosomes in various organisms


Chromosome numbers (2n) in some plants
Plant Species #
Arabidopsis thaliana 10
Rye 14
Maize 20
Einkorn wheat[10] 14
Durum wheat[10] 28
Bread wheat[10] 42
Wild tobacco[citation needed] 24
Cultivated tobacco 48
Adder's Tongue Fern[11] 1262
Chromosome numbers (2n) in some animals
Species # Species #
Common fruit fly 8 Guinea Pig [12] 64
Dove[citation needed] 16 Snail[citation needed] 24
Earthworm[13] 36 Tibetan fox 36
Domestic cat 38 Domestic pig 38
Lab mouse 40 Lab rat 42
Rabbit[citation needed] 44 Syrian hamster 44
Hare[citation needed] 46 Human[14] 46
Gorillas, Chimpanzees[14] 48 Domestic sheep 54
Elephants[15] 56 Cow 60
Donkey 62 Horse 64
Dog[16] 78 Chicken[17] 39
Goldfish[18] 100-104 Silkworm[19] 28
Chromosome numbers in other organisms
Species Large
Trypanosoma brucei 11 6 ~100

The 24 human chromosome territories during prometaphase in fibroblast cells.
The 24 human chromosome territories during prometaphase in fibroblast cells.

Normal members of a particular eukaryotic species all have the same number of nuclear chromosomes (see the table). Other eukaryotic chromosomes, i.e., mitochondrial and plasmid-like small chromosomes, are much more variable in number, and there may be thousands of copies per cell.

Asexually reproducing species have one set of chromosomes, which is the same in all body cells.

Sexually reproducing species have somatic cells (body cells), which are diploid [2n] having two sets of chromosomes, one from the mother and one from the father. Gametes, reproductive cells, are haploid [n]: they have one set of chromosomes. Gametes are produced by meiosis of a diploid germ line cell. During meiosis, the matching chromosomes of father and mother can exchange small parts of themselves (crossover), and thus create new chromosomes that are not inherited solely from either parent. When a male and a female gamete merge (fertilization), a new diploid organism is formed.

Some animal and plant species are polyploid [Xn]: they have more than two sets of homologous chromosomes. Agriculturally important plants such as tobacco or wheat are often polyploid compared to their ancestral species. Wheat has a haploid number of seven chromosomes, still seen in some cultivars as well as the wild progenitors. The more common pasta and bread wheats are polyploid, having 28 (tetraploid) and 42 (hexaploid) chromosomes compared to the 14 (diploid) chromosomes in the wild wheat.[20]


Prokaryote species generally have one copy of each major chromosome, but most cells can easily survive with multiple copies.[21] Plasmids and plasmid-like small chromosomes are, like in eukaryotes, very variable in copy number. The number of plasmids in the cell is almost entirely determined by the rate of division of the plasmid - fast division causes high copy number, and vice versa.


Figure 3: Karyogram of a human male
Figure 3: Karyogram of a human male

In general, the karyotype is the characteristic chromosome complement of a eukaryote species.[22] The preparation and study of karyotypes is part of cytogenetics.

Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karotypes, which are often highly variable. There may be variation between species in chromosome number and in detailed organization. In some cases there is significant variation within species. Often there is variation 1. between the two sexes. 2. between the germ-line and soma (between gametes and the rest of the body). 3. between members of a population, due to balanced genetic polymorphism. 4. geographical variation between races. 5. mosaics or otherwise abnormal individuals. Finally, variation in karyotype may occur during development from the fertilised egg.

The technique of determining the karyotype is usually called karyotyping. Cells can be locked part-way through division (in metaphase) in vitro (in a reaction vial) with colchicine. These cells are then stained, photographed and arranged into a karyogram, with the set of chromosomes arranged, autosomes in order of length, and sex chromosomes (here XY) at the end: Fig. 3.

Like many sexually reproducing species, humans have special gonosomes (sex chromosomes, in contrast to autosomes). These are XX in females and XY in males.

Historical note

Investigation into the human karyotype took many years to settle the most basic question: how many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism.[23] Painter in 1922 was not certain whether the diploid number of man was 46 or 48, at first favouring 46.[24] He revised his opinion later from 46 to 48, and he correctly insisted on man having an XX/XY system.[25] Considering their techniques, these results were quite remarkable.

New techniques were needed to definitively solve the problem:

1. Using cells in culture 2. Pretreating cells in a hypotonic solution, which swells them and spreads the chromosomes 3. Arresting mitosis in metaphase by a solution of colchicine 4. Squashing the preparation on the slide forcing the chromosomes into a single plane 4. Cutting up a photomicrograph and arranging the result into an indisputable karyogram.

It took until the mid 1950s until it became generally accepted that the karyotype of man included only 46 chromosomes.[26][27] Rather interestingly, the great apes have 48 chromosomes.

Chromosomes in prokaryotes

The prokaryotes - bacteria and archaea - typically have a single circular chromosome, but many variations do exist.[1] Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacteria Candidatus Carsonella ruddii,[2] to 12,200,000 base pairs in the soil-dwelling bacteria Sorangium cellulosum.[3] Spirochaetes of the genus Borrelia are a notable exception to this arrangement, with bacteria such as Borrelia burgdorferi, the cause of Lyme disease, containing a single linear chromosome.[4]

Structure in sequences

Prokaryotes chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a single point (the origin of replication) from which replication starts, while some archaea contain multiple replication origins.[5] The genes in prokaryotes are often organised in operons, and do not contain introns, unlike eukaryotes.

DNA packaging

Prokaryotes do not possess nuclei, instead their DNA is organized into a structure called the nucleoid.[6] The nucleoid is a distinct structure and occupies a defined region of the bacterial cell. This structure is however dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome.[7] In archaea, the DNA in chromosomes is even more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes.[8][9]

Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes (and the attached DNA).

Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled. The DNA must first be released into its relaxed state for access for transcription, regulation, and replication.