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Epistasis is when the phenotype of one gene is affected by one or more other genes. [21] This is often through some sort of masking effect of one gene on the other. [ 22 ] For example, the "A" gene codes for hair color, a dominant "A" allele codes for brown hair, and a recessive "a" allele codes for blonde hair, but a separate "B" gene controls ...
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 expression plays a crucial role in determining the phenotypes of organisms. The level of gene expression can affect the phenotype of an organism. For example, if a gene that codes for a particular enzyme is expressed at high levels, the organism may produce more of that enzyme and exhibit a particular trait as a result. On the other hand ...
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.
Epigenetic mechanisms. In biology, epigenetics is the study of heritable traits, or a stable change of cell function, that happen without changes to the DNA sequence. [1] The Greek prefix epi-(ἐπι-"over, outside of, around") in epigenetics implies features that are "on top of" or "in addition to" the traditional (DNA sequence based) genetic mechanism of inheritance. [2]
Punnett square for the agouti gene in mice, demonstrating a recessive lethal allele. [2] Lethal alleles were first discovered by Lucien Cuénot in 1905 while studying the inheritance of coat colour in mice. The agouti gene in mice is largely responsible for determining coat colour. The wild-type allele produces a blend of yellow and black ...
The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34). [32] The I A allele gives type A, I B gives type B, and i gives type O. As both I A and I B are dominant over i, only ii people have type O blood.
An inducible gene is a gene whose expression is either responsive to environmental change or dependent on the position in the cell cycle. Any step of gene expression may be modulated, from the DNA-RNA transcription step to post-translational modification of a protein. The stability of the final gene product, whether it is RNA or protein, also ...