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Homologous Definition
The term “homologous” is used in general science to describe a degree of resemblance. It might be in terms of position, structure, function, or personality traits. Homologous refers to a collection of molecules or chemicals that differ by a consistent amount. Alkanes, for example, are a homologous group of hydrocarbons that includes methane, ethane, propane, and others.
They have chemical characteristics that are comparable and follow a pattern. For example, when the length of their chain lengthens (due to the addition of CH2), the boiling point rises. In biology and genetics, what does homologous mean? In essence, they both describe homologous as having the same anatomical locations, matching components, and similar structures.
It is used in biology to refer to body parts or structures that have a shared evolutionary origin, such as “homologous structures.” It refers to a pair of chromosomes that have a similar structure in genetics. Homologous chromosomes are chromosomes that are paired based on chromosomal length and gene sequence. Homologous is derived from the Greek homologos, which means “agreeing” or “correspondent.”
Homologous vs Heterologous
Both heterologous and homologous are descriptive terms, yet their meanings are diametrically opposed. While homologous refers to biological organisms with a matching or similar trait, heterologous refers to creatures with features that are significantly different.
A heterologous tumor, for example, is one that contains cytologic components or tissue from a different location than the tumor’s origin. A homologous tumor, on the other hand, is made up of cells or tissue that closely resembles the tissue in which it develops.
Homologous Examples
i. Homologous Structure
Homologous structures are bodily components that share anatomical characteristics, indicating a shared ancestor or developmental origin. They may have the same characteristics, but they don’t always serve the same purpose. The forelimbs of bats and humans, for example, are both homologous structures.
Bat forelimbs are made up of the same bones as human forelimbs. This implies the presence of a common ancestor organism. The anatomical characteristics of the various animal forelimbs are depicted in the diagram below.
Bats and humans have many of the same forelimb bone components. The humerus, radius, ulna, carpal, and phalanges are the same or equivalent forelimb bones of cats, whales, lizards, and birds. However, the primary function of the forelimbs of various animals differs. Bats, for example, primarily use their forelimbs for gliding.
They are used by the birds to fly. They are used by cats and lizards for walking and climbing. They are used by whales to swim through. Because humans lack a wing membrane and are bipedal, their arms are free to perform a wide range of activities, including reaching, grabbing, climbing, swimming, and so on.
ii. Homologous Chromosomes
Homologous chromosomes are chromosomes that are paired together. The gene sequence, loci, and centromere position are all the same in a pair of chromosomes. They are also chromosomally identical. They may, however, have different alleles. In the nucleus of a human cell, for example, there are 46 chromosomes. The mother provides half of them (23 chromosomes), while the father provides the other half (23 chromosomes).
These chromosomes join during fertilization to produce a new nucleus within the zygote cell, which then grows and develops into a new human being. These two sets of chromosomes will be found in every human cell. 22 of these pairings are homologous autosomes. The remaining chromosomes are sex chromosomes. Two X chromosomes are also homologous, but a pair of sex chromosomes made up of X and Y will be heterologous rather than homologous.
Homologous Citations
- Recombination, Pairing, and Synapsis of Homologs during Meiosis. Cold Spring Harb Perspect Biol . 2015 May 18;7(6):a016626.
- Mechanism and significance of chromosome damage repair by homologous recombination. Essays Biochem . 2020 Oct 26;64(5):779-790.
- Homologous chromosome pairing in meiosis of higher eukaryotes-still an enigma? Genome . 2020 Oct;63(10):469-482.
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