What Are Autosomes?
Autosomes are the chromosomes within eukaryotic, sexually reproducing organisms that are not involved in determining the sex of an organism. Sex chromosomes, also known as allosomes, determine the sexual characteristics of a number of species. Autosomes are always found in homologous pairs when found in a diploid organism. The sex chromosomes are typically unmatched.
In other species, the autosomes account for the entire genetic code, and sex is determined through different methods. In humans, the autosomes account for 44 of the 46 chromosomes present, and exclude only the X and Y chromosomes. Below are examples of autosomes in humans and other organisms.
Examples of Autosomes
Autosomes in Humans
In humans there are 44 autosomes in 22 pairs. In a typical human karyotype (an organized image of chromosome pairs) you can see these pairs, along with the sex chromosomes. In humans the sex chromosomes are X and Y. An individual with XX is female, XY is male, and sometimes a person can have a variable number of these sex chromosomes which can lead to varied characteristics. A diagram can be seen below of a karyotype and the actual chromosomes as imaged in the cell.
Each of the autosome pairs is typically an equal length, because they contain the same genes. For instance, a certain gene on the 7th chromosome pair is responsible for the protein which allows you to taste a certain bitter chemical found in foods like broccoli and spinach. Each chromosome in the pair will contain an allele, or form of the gene. If either of the alleles is functional, you can taste the bitter chemical. This is an example of a dominant trait.
If both of the alleles are nonfunctional, you will not be able to taste the bitter as much. This may help explain people’s variable food preferences. Most other traits are encoded on the autosomes, and interact together to produce an entire human body. These traits come about through the interaction of proteins, encoded by genes on the autosomes. Typically only a small amount of information is provided by the sex chromosomes, though they are also needed.
Autosomes in Birds
Birds functions in a similar way to humans, placing most of their DNA in autosomes, but having two chromosomes reserved for sex chromosomes. The autosomes of birds are also paired, though birds tend to have many more autosomes than humans. The typical bird genome contains around 80 autosomes, with 2 reserved for sex determination.
The autosomes in birds function just like the autosomes in humans, though they produce different proteins. Together, the interactions of these proteins produce an entirely different organism compared to humans.
The allosomes of birds operate the same as in humans, with one major twist. Instead of the male having a heterogametic genotype (XY), the females in birds are heterogametic (ZW). This refers to the fact that during meiosis, they will produce gametes with either a Z chromosome or a W chromosome. In birds, males are (ZZ).
Autosomes in Other Species
While some groups like birds, are similar to humans, other species have only autosomes and determine their sex through other methods. These species may be diploid or haploid and reproduce sexually or asexually. But, because there are no chromosomes which determine sexual characteristics by their presence alone, all the chromosomes are autosomes.
This process can be seen in the Hymenoptera, the group containing bees and ants. Within this group, organisms typically determine their genetics based on the ploidy of their cells. This condition is known as haplodiploidy. Unlike humans, the different genders of bees and ants have different numbers of chromosomes. In these systems nearly all the individuals are female and diploid. The males are called drones, have only a haploid genome, and are typically only used to create sperm and reproduce.
Another group which uses only autosomes in their genetics are reptiles. These organisms often depend on a temperature-dependent system of sex determination. In lizards, alligators, and some other reptiles, males are created in warmer temperatures, while females are created with cooler temperatures. The autosomes are all present, in both genders, but the temperature determines how the genes are transcribed into proteins. This, in turn, determines the sex of the organism.
Interestingly, turtles and tortoises also share this temperature-dependent system which relies on autosomes. But, their version is backwards. Males are created with warmth, females with lower temperatures. Though the autosomes of turtles are similar to the autosomes of lizards and alligators, the groups diverged a very long time ago. In turn, the genes on the autosomes react differently to the same temperature, and the sex determination pattern is reversed.
Other organisms that rely solely on autosomes include a number of fish species. Unlike the organisms above, these fish rely on a number of different environmental factors to determine their sex. Thus, each fish has the same number and type of autosomes, all with a matching pair. In some species on the coral reef, the fish are all males except 1. This is the largest fish, and she only changes into a female once she is the biggest and most dominant. Other fish start life as one gender, and as their autosomes change over time they become the other gender.
Autosomes and Genetic Testing
Human autosomes are a large part of DNA testing, whether for ancestry or health reasons. The autosomes contain a majority of the human genome, and can provide a wealth of information. Most direct-to-consumer DNA testing companies offer autosomal testing, which tests the sequences present on the autosome. They do this by cutting the DNA into small fragments, and testing for the presence of small, identifiable segments of DNA known as single nucleotide polymorphisms, or SNPs. These SNPs can tell scientist which allele of a gene you carry, as well as where that allele originated geographically.
Other DNA testing services offer information about your genetic health, and which alleles may have the potential to increase your risk for disease. Autosomal disorders are genetic disorders carried on the autosomes, and many DNA tests can tell if you are a carrier of alleles for these diseases. While this information is useful, it is usually only a small increase or decrease in your overall risk. Most diseases have a strong lifestyle factor associated. Still other companies offer services based on your autosomes, such as DNA-matched flavor profiles for your wine, or music playlists based on your genetics. These last services are typically not based on any sound science.
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