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Homology has to be distinguished from analogy; for instance, the wings of insects and the wings of birds are analogous but not homologous. These similar structures most likely evolved through different pathways, a process known as convergent evolution.
Males and females share almost the same genome, and it is much easier and more efficient to make slight modifications to a single body plan than to come up with two different plans altogether. Rather than have one section of the genome make an ovary and another section make a testicle, one section forms the common precursor of both and then things change slightly towards the end, under the action of hormones. If something is easier and more efficient, evolution is more likely to find it. However it doesn't always find it: even though the vas deferens in males and the fallopian tube in females perform a very similar function, they are not homologous but analogous: they are constructed separately from scratch.
Other homologous structures include the clitoris and the penis, as well as the nipples in both sexes.
In genetics, homology is used in reference to proteinmyoglobin, showing coloured alpha helices. This protein was the first to have its structure solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, which led to them receiving a Nobel Prize in Chemistry. A protein is a complex, or DNADeoxyribonucleic acid DNA is a nucleic acid which carries genetic instructions for the biological development of all cellular forms of life and many viruses. DNA is sometimes referred to as the molecule of heredity as it is inherited and used to propagate sequencesFor the sense of "sequencing" used in electronic music, see the music sequencer article. In genetics and biochemistry, sequencing means to determine the primary structure (or primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic, meaning that the given sequences share ancestry.
Homology among proteins and DNA is often concluded on the basis of sequence similarity, especially in bioinformaticsBioinformatics or computational biology is the use of mathematical and informational techniques, including statistics, to solve biological problems, usually by creating or using computer programs, mathematical models or both. One of the main areas of bioi. For example, in general, if two genes have an almost identical DNA sequence, it is likely that they are homologous. However, it may be that the sequence similarity did not arise from their sharing a common ancestor; short sequences may be similar by chance, or sequences may be similar because both were selected to bind to a particular protein, such as a transcriptionTranscription may be one of the following: In linguistics, transcription is the conversion of spoken words into written language. In genetics, transcription is the process of copying DNA to RNA by an enzyme called RNA polymerase (RNAP). In music transcrip factor. Such sequences are similar but not homologous. Many algorithms exist to cluster protein sequences into sequence families, which are sets of mutually homologous sequences. (See sequence clusteringIn bioinformatics, sequence clustering algorithms attempt to group sequences that are somehow related. The sequences can be either of genomic, "transcriptomic" ( ESTs) or protein origin. For proteins, homologous sequences are typically grouped into famili and sequence alignmentSequence alignment is an arrangement of two or several biological sequences (e. protein sequences or DNA sequences) highlighting their similarity. The sequences are padded with gaps (usually denoted by dashes) so that wherever possible columns contain ide.)
Homology of sequences can be of two types: orthology or paralogy. Sequences are orthologous if they are homologous and were separated by a speciationSpeciation refers to the appearance of a new species of life on earth, particular as seen in the fossil record. There are many ideas about the process leading to the creation of new species, each typically based on any of the Darwinian theories of biologi event; if a gene exists in a species, and that species diverges into two species, then the copies of this gene in the resulting species are orthologous. Sequences are paralogous if they are homologous and were separated by a gene duplication event; if a gene in an organism is duplicated, each copy of the gene is paralogous to the other. A pair of sequences that are orthologous to each other are called orthologs, a pair that are paralogous are called paralogs.
A homologous pair of chromosomes in a diploid cell is a matching pair of chromosomes, one derived from each parent of the organism. Except for the sex chromosomes, the chromosomes of each homologous pair share significant sequence similarity across their entire length, and thus typically contain the same sequence of genes. The sex chromosomes have a shorter region of sequence similarity. Based on the sequence similarity and our knowledge of biology, we can presume that the chromosomes are paralogous.