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The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual mitochondria. These are usually treated separately as the nuclear genome and the mitochondrial genome. [1]
The first genome to be sequenced was that of the virus φX174 in 1977; [4] the first genome sequence of a prokaryote (Haemophilus influenzae) was published in 1995; [5] the yeast (Saccharomyces cerevisiae) genome was the first eukaryotic genome to be sequenced in 1996. [6]
The DNA sequence assembly alone is of little value without additional analysis. [9] Genome annotation is the process of attaching biological information to sequences, and consists of three main steps: [68] identifying portions of the genome that do not code for proteins; identifying elements on the genome, a process called gene prediction, and
Genome sizes and corresponding composition of six major model organisms as pie charts. The increase in genome size correlates with the vast expansion of noncoding (i.e., intronic, intergenic, and interspersed repeat sequences) and repeat DNA (e.g., satellite, LINEs, short interspersed nuclear element (SINEs), DNA (Alu sequence), in red) sequences in more complex multicellular organisms.
[1] [2] This requires both zygotic genome activation (ZGA) and degradation of maternal products. This process is important because it is the first time that the new embryonic genome is utilized and the paternal and maternal genomes are used in combination (ie. different alleles will be expressed). The zygotic genome now drives embryo development.
The animations have a non-descript musical background and are purposely not narrated to maximize use. These animations may be played alone or simultaneously with the spoken definition of the term. All cellular organelles have animation sequences, as do many key terms such as gene, cell, ACGT, and chromosome. Spoken Explanations of Glossary Terms:
The methylation of nucleobases in a DNA molecule inhibits recognition of the methylated sequence by DNA-binding proteins, which can effectively silence the expression of genes. Specific residues within histones are also commonly methylated, which can change nucleosome positioning and similarly activate or repress nearby loci.
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.