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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]
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 ...
ABC model of flower development guided by three groups of homeotic genes.. The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower.
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 ]
An entire gene family may also be lost, or gained through de novo gene birth, by such extensive divergence such that a gene is considered part of a new family, or by horizontal gene transfer. When the number of genes per genome remains relatively constant, this implies that genes are gained and lost at relatively same rates.
A null allele is a gene variant that lacks the gene's normal function because it either is not expressed, or the expressed protein is inactive. For example, at the gene locus for the ABO blood type carbohydrate antigens in humans, [13] classical genetics recognizes three alleles, I A, I B, and i, which determine compatibility of blood transfusions.
Gene structure is the organisation of specialised sequence elements within a gene. Genes contain most of the information necessary for living cells to survive and reproduce. [ 1 ] [ 2 ] In most organisms, genes are made of DNA, where the particular DNA sequence determines the function of the gene.
Their expression patterns in the early embryo are determined by the maternal effect gene products and shown in the diagrams on the right side of this page. The gap genes are part of a larger family called the segmentation genes. These genes establish the segmented body plan of the embryo along the anterior-posterior axis.