Overlapping genes are particularly common in rapidly evolving genomes, such as those of viruses, bacteria, and mitochondria.
Overlapping genes are relatively common in DNA and RNA viruses. There are several examples in bacterial and eukaryotic genomes, but, in general, overlapping genes are quite rare in organisms other than viruses. There have been a few reports of overlapping genes in mammalian genomes.
Overlapping genes, also called “dual-coding genes”, are regions of DNA or RNA that are translated in two different reading frames to yield two different proteins.
Overlapping genes (OLGs) are two adjacent DNA segments that are partially or entirely overlapped with each other through a shared genomic location. These genes are present in the viral, prokaryotic, and eukaryotic genomes.
The evolutionary origin of overlapping genes is not yet clear. Recent research indicates that they may have arisen due to several mutational events. These may include the loss of a signal to stop the transcription process in a gene and a shift in the reading sequence of the genetic components.
Sequence similarity is a major player in crossover – crossover events are more likely to occur in long regions of close identity on a gene. This means that any section of the genome with long sections of repetitive DNA is prone to crossover events.
The percentage of overlapping genes in a genome varies across species: 5–14% in vertebrates [5], 10–50% in bacteria [6], and up to 100% in viruses (e.g., hepatitis B virus)[7].
These overlaps are typically assumed to be a form of genome compression, allowing the virus to increase its repertoire of proteins without increasing its genome length (Barrell et al.
Which of the following organisms have overlapping genes? Explanation: The viruses have overlapping genes to accommodate the genome in such a small cell.
Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination.
An example with three human overlapping genes— MUTYH, TOE1, and TESK2—is presented in Figure 1. The gene TOE1 has overlapping exons with MUTYH at the 5′-end and with TESK2 at the 3′-end. In the human genome we also found a segment with four exon overlapping genes: LOC338549, IDI2, HT009, and IDI1.
Regions of the world can and do overlap such as the areas of Southeast Asia and Asia. Regions also have transitional boundaries like between North Africa and Sub-Saharan Africa.
Overlapping gene coding sequences (CDSs) occur where a nucleotide sequence codes for two different amino acid sequences in different read-frames. There are five possible read-frames for a 'secondary' open reading frame (ORF) relative to a 'primary' ORF that we label −3, −2, −1, +1 and +2 (Fig. 1).
Mutually exclusive and overlapping events are examples of compound events. Mutually exclusive events are events that have no outcomes in common. Overlapping events are events that have one or more outcomes in common.
Repetitive DNA sequences such as telomeres and centromeres are, like the chromosomes in which they reside, highly dynamic within the interphase nucleus, moving about by diffusion.
The overlapping zone or transition zone between two different ecosystems is called ecotone. Ecozones are a method of dividing up the earth's surface. Each ecozone is a large area that contains a number of habitals, linked by the evolutionary history of the organisms within them.
Overlapping genes (genes partially or entirely overlapping) represent a genomic feature that is shared widely across biological organisms ranging from viruses to multi-cellular organisms. In bacteria, a third of the annotated genes are involved in an overlap.
Gene overlapping is widely employed by RNA viruses to generate genetic novelty while retaining a small genome size. However, gene overlapping also increases the deleterious effect of mutations as they affect more than one gene, thereby reducing the evolutionary rate of RNA viruses and hence their adaptive capacity.
Overlapping genes are adjacent genes that overlap partially or entirely. Overlapping gene pairs extracted from complete bacterial genome sequences were classified into three directional patterns, namely, 'convergent' (--><--), 'unidirectional' (-->-->), and 'divergent' (<---->).
Often, the overlap is only between the 5′ untranslated region (UTR) or 3′ UTR of both transcripts (5′ UTR overlap shown)10,170. (Bottom) In contrast, prokaryote and virus genes are only considered to overlap if their coding sequences overlap5,27.
Overlapping genes, also called “dual-coding genes”, were first discovered by Barrell et al. [11] in the genome of ΦX174, a small single-stranded DNA virus (5386 nt) that infects Escherichia coli.
Children receive their autosomal DNA from both parents in approximately equal proportions – resulting in considerable (≈50%) overlap in their genes.
The closer two genes were to one another on a chromosome, the greater their chance of being inherited together. In contrast, genes located farther away from one another on the same chromosome were more likely to be separated during recombination.
Comparing Human Genetic Similarity to Other Life Forms
Of the three billion genetic building blocks that make us living things, only a handful are uniquely ours. In fact, despite our differences on the outside, humans are 99.9% genetically similar to one another.
Chiasmata represents the site of crossing over. It is the point at which two homologous non-sister chromatids exchange genetic material.