2 minute read
Key Takeaways
function so there is a neutral molecular evolution of the gene. Some genes are naturally resistant to mutation, while others are more susceptible and change more rapidly.
Most new genes come from gene duplication, which creates more copies of an existing gene. The genes together form a paralog, which diverges in sequence and function. This is how biodiversity occurs. Sometimes a mutation results in a nonfunctional protein, in which case, it is called a pseudogene.
Advertisement
Orphan genes are genes that code for no existing gene. This is an extremely rare occurrence that is usually caused by a gene duplication followed by a sequence change that creates an orphan protein that has no similarity to any other protein. The original relationship between the protein and its precursor gene is undetectable. It is possible for these types of genes to have a function that creates a different phenotype or even a different species.
The size of a given genome and the number of genes encoded within the genome is widely variant from organism to organism. The smallest genomes occur in viruses and viroids (which are single non-coding RNA gene organisms). Plants have very large genomes compared to animals with the total number of protein-coding genes in the entire earth being about five million. In humans, there are about 20,000 protein-coding genes and only about 13 coding genes in the mitochondrial genome. The rest of the genome is non-coding. Remember that all genes available to an organism are found in every cell of the multicellular organism but only certain numbers of genes get encoded per cell, depending on what type of cell is involved.
Essential genes are believed to be called this because they are crucial for the organism’s survival. This assumes that there is an abundance of all of the available nutrients for the cell and no environmental stress that inhibits the transcription of the gene. Only a few genes are actually essential. Humans are believed to have about two thousand essential genes, which is only about ten percent of our genes. Essential genes are housekeeping genes and genes necessary for the development of the organism or the life cycle of the organism.
• DNA or deoxyribonucleic acid is the basic genetic structure in almost all organisms except for a few viruses.
• DNA contains long sequences of nucleotides, labeled adenine, guanine, cytosine, and thymine. • DNA is packed into chromosomes in eukaryotes but is circular in prokaryotes. • The basic coding segment of a piece of DNA is the gene, which has promoter regions, transcribed regions, and regulating regions.
