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The stability of the final gene product, whether it is RNA or protein, also contributes to the expression level of the gene—an unstable product results in a low expression level. In general gene expression is regulated through changes [ 47 ] in the number and type of interactions between molecules [ 48 ] that collectively influence ...
A measurement of the amount of gene product is sometimes used to infer how active a gene is. Abnormal amounts of gene product can be correlated with disease-causing alleles, such as the overactivity of oncogenes, which can cause cancer. [1] [2] A gene is defined as "a hereditary unit of DNA that is required to produce a functional product". [3]
In the budding yeast Saccharomyces cerevisiae the number of essential genes is slightly higher, at 1000 genes (~20% of their genes). [110] Although the number is more difficult to measure in higher eukaryotes, mice and humans are estimated to have around 2000 essential genes (~10% of their genes). [ 111 ]
A regulator gene may encode a protein, or it may work at the level of RNA, as in the case of genes encoding microRNAs. An example of a regulator gene is a gene that codes for a repressor protein that inhibits the activity of an operator (a gene which binds repressor proteins thus inhibiting the translation of RNA to protein via RNA polymerase). [1]
Due to the similarity of their sequences and their overlapping functions, individual genes in the family often share regulatory control elements. [6] [8] In some instances, gene members have identical (or nearly identical) sequences. Such families allow for massive amounts of gene product to be expressed in a short time as needed.
Cis-regulatory DNA sequences that are located in DNA regions distant from the promoters of genes can have very large effects on gene expression, with some genes undergoing up to 100-fold increased expression due to such a cis-regulatory sequence. [3] These cis-regulatory sequences include enhancers, silencers, insulators and tethering elements. [4]
[11] [12] Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene-related phenotype. [ 13 ] [ 14 ] [ clarification needed ] There are many ways to introduce foreign DNA to a cell for expression, and many different host cells may be used for expression — each expression system has distinct ...
The Punnett square works, however, only if the genes are independent of each other, which means that having a particular allele of gene "A" does not alter the probability of possessing an allele of gene "B". This is equivalent to stating that the genes are not linked, so that the two genes do not tend to sort together during meiosis.