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E1, E2, E3

E1, E2, E3  

The first, second, and third generation of organisms following some experimental manipulation, such as irradiation with x-rays.
gradient analysis

gradient analysis  

An ordination technique for the description of vegetation based on characteristics of the site rather than the composition of species. One or more environmental gradients are identified and stands ...
Xenopus

Xenopus  

A genus of aquatic anurans found in sub-Saharan Africa. They are commonly called South African clawed frogs. The 16 species in the genus have genome sizes that range from 3.5 × 109 bp to 1.6 × 1010 ...
human mitotic chromosomes

human mitotic chromosomes  

The number of human chromosomes observed at mitosis was incorrectly reported as 24 pairs by W. Flemming in 1898. It was not until 1956 that the correct number was determined as 23 pairs by J. H. Tjio ...
dosage compensation

dosage compensation  

A genetic process that compensates for genes that exist in two doses in the homogametic sex and one in the heterogametic sex as a result of their location on the X-chromosome. The process is not ...
Mus musculus

Mus musculus  

The laboratory mouse. Its diploid chromosome number is 20, and extensive genetic maps are available for the 19 autosomes and the X chromosome. There are large collections of strains containing ...
sex chromosome

sex chromosome  

The homologous chromosomes that are dissimilar in the heterogametic sex. See X chromosome, W, Z chromosomes, Y chromosomes.
Drosophila melanogaster

Drosophila melanogaster  

Commonly called the “fruit fly,” this species is a model organism for the study of specific genes in multicellular development and behavior. Its haploid genome contains about 176 million nucleotide ...
repetitive DNA

repetitive DNA  

Any DNA sequence which occurs many times within a genome; it may be in a tandem array or dispersed repeats.
biochemistry

biochemistry  

The study of the chemistry of living organisms, especially the structure and function of their chemical components (principally proteins, carbohydrates, lipids, and nucleic acids). Biochemistry has ...
ultrasonics

ultrasonics   Quick reference

A Dictionary of Biology (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Life Sciences
Length:
46 words

...ultrasonics The study and use of pressure waves that have a frequency in excess of 20 000 Hz and are therefore inaudible to the human ear. Ultrasound is used in medical diagnosis, particularly in conditions such as pregnancy, in which X-rays could have a harmful...

Monodelphis domestica

Monodelphis domestica   Quick reference

A Dictionary of Genetics (8 ed.)

Reference type:
Subject Reference
Current Version:
2014
Subject:
Science and technology, Life Sciences
Length:
105 words

...opossum, the most widely used, laboratory-bred marsupial, and the first to have its genome sequenced. The genome of this species contains 18,000 to 20,000 protein-coding genes, the vast majority of which have eutherian orthologs. Its haploid chromosome number is 9, and its autosomes are all larger than the largest human autosome. However, its X chromosome is relatively small (half the size of the human X). This species belongs to the family Didelphidae , and the marsupials of Australia are all descendants of South American opossums. See Appendix A ,...

retinitis pigmentosa

retinitis pigmentosa   Reference library

Oxford Dictionary of Biochemistry and Molecular Biology (2 ed.)

Reference type:
Subject Reference
Current Version:
2008
Subject:
Science and technology, Life Sciences
Length:
168 words

...histidine residue at position 23 in the opsin molecule, causing the characteristic retinal degeneration. Another severe form of the disease, affecting up to around 20% of some populations, is X‐linked; it usually becomes manifest within the first two decades of life and progresses to blindness within 10–20 years. The gene, named RPGR , for this form has now been found on the short arm of the X‐chromosome. The predicted 90 kDa protein product of the RPGR gene bears significant homology to the RCC1 family...

nitrophorin

nitrophorin   Reference library

Oxford Dictionary of Biochemistry and Molecular Biology (2 ed.)

Reference type:
Subject Reference
Current Version:
2008
Subject:
Science and technology, Life Sciences
Length:
74 words

...abbr. : NP; a monomeric hemoprotein (≈20 kDa) secreted in saliva of the blood‐sucking reduviid bug Rhodnius prolixus . There are four nitrophorins (NP 1 to 4), which are homologous and contain a conserved eight‐stranded beta barrel. They carry nitric oxide, which causes smooth muscle relaxation and vasodilation in the host. They also bind histamine and reduce the inflammatory and immune responses in the host. NP2 (also called prolixin‐S) inhibits activation of clotting factor X...

X-rays

X-rays   Reference library

The Oxford Companion to the Body

Reference type:
Subject Reference
Current Version:
2003
Subject:
Science and technology, Life Sciences
Length:
1,613 words
Illustration(s):
2

...was appreciated of the dangers of X-rays and protection was unknown, but the hazards all too soon became apparent. Frequent exposure led to radiation burns, loss of fingers, and fatal skin cancers. A Martyr's Memorial was erected in Hamburg in 1936 by the German Röntgen Society, inscribed with the names of 169 X-ray and radium martyrs from 15 countries who by then had died; the highest tolls recorded were 14 British, 20 German, 39 American, and 40 French. Twenty-eight more British names were later added. It was not until the 1920s that any protective...

Xenopus

Xenopus   Quick reference

A Dictionary of Genetics (8 ed.)

Reference type:
Subject Reference
Current Version:
2014
Subject:
Science and technology, Life Sciences
Length:
245 words

...number for the genus appears to have been 18, but there are now species with 36, 72, and 108 chromosomes. X. laevis and X. borealis are favorites for research in molecular genetics. Studies on the nucleolar mutants of X. laevis have shown that the nucleolus contains about 450 rRNA genes. This frog has one class of 5S rRNA genes transcribed in the oocyte and another in somatic cells. In Xenopus lampbrush chromosomes there are about 20,000 copies of the oocyte 5S rRNA genes per haploid genome, and these are distributed among large chromomeres that...

copy number

copy number   Quick reference

A Dictionary of Biology (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Life Sciences
Length:
118 words

...cause copy number variation . These variations can affect up to 20% of the genome in humans. Some occur in stretches of DNA between genes where they may have little or no impact, whereas others can affect gene function and cause disease. For example, a three-nucleotide sequence is often found repeated numerous times in tandem, forming a series of trinucleotide repeats. Expansion of these near to or within certain genes results in several human diseases, such as Huntington disease and fragile X syndrome. Compare single nucleotide polymorphism...

biochemistry

biochemistry   Quick reference

A Dictionary of Biology (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Life Sciences
Length:
170 words

...The study of the chemistry of living organisms, especially the structure and function of their chemical components (principally proteins, carbohydrates, lipids, and nucleic acids). Biochemistry has advanced rapidly with the development, from the mid-20th century, of such techniques as chromatography, spectroscopy, X-ray diffraction, radioisotopic labelling, and electron microscopy. Using these techniques to separate and analyse biologically important molecules, the steps of the metabolic pathways in which they are involved (e.g. glycolysis and the Krebs...

Caenorhabditis elegans

Caenorhabditis elegans   Quick reference

A Dictionary of Genetics (8 ed.)

Reference type:
Subject Reference
Current Version:
2014
Subject:
Science and technology, Life Sciences
Length:
252 words

...has been extensively investigated. The worm is about 1 mm in length, and its life cycle, when reared at 20°C, is 3.5 days. Its transparent cuticle allows the visualization of every cell. The adult has 816 somatic cells, of which 302 are neurons. The complete lineage history and fate of every cell is known. C. elegans normally reproduces as a self-fertilizing hermaphrodite, which has two X chromosomes per cell, plus five pairs of autosomes. Loss of an X by meiotic nondisjunction leads to the production of males. These arise spontaneously among the progeny of...

human mitotic chromosomes

human mitotic chromosomes   Quick reference

A Dictionary of Genetics (8 ed.)

Reference type:
Subject Reference
Current Version:
2014
Subject:
Science and technology, Life Sciences
Length:
195 words

...chromosomes with submedian centromeres. Group C (chromosomes 6–12 and the X chromosome)—medium-sized chromosomes with submedian centromeres. Group D (chromosomes 13–15)—medium-sized acrocentric chromosomes. Chromosome 13 has a prominent satellite on the short arm. Chromosome 14 has a small satellite on the short arm. Group E (chromosomes 16–18)—rather short chromosomes with approximately median (in chromosome 16) or submedian centromeres. Group F (chromosomes 19 and 20)—short chromosomes with approximately median centromeres. Group G (chromosomes 21,...

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