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Autosomal DNA is the most important and most commonly tested type of DNA. A child will have exactly half of their autosomal DNA from each parent. However, a child will usually not have exactly 25% from each grandparent. A child could have 20% from one grandparent and 30% from another grandparent for example. This is because each child is randomly given half of their parent's DNA. When a new sperm or egg is formed, the pairs chromosomes in the parent line and exchange information, meaning segments are randomly cut out and switch places with each other to form new chromosomes that are a mixture of the previous ones. The child is then given one chromosome from each pair and the other is discarded. This happens in both parents so that the child receives one full set of chromosomes from each parent. | Autosomal DNA is the most important and most commonly tested type of DNA. A child will have exactly half of their autosomal DNA from each parent. However, a child will usually not have exactly 25% from each grandparent. A child could have 20% from one grandparent and 30% from another grandparent for example. This is because each child is randomly given half of their parent's DNA. When a new sperm or egg is formed, the pairs chromosomes in the parent line and exchange information, meaning segments are randomly cut out and switch places with each other to form new chromosomes that are a mixture of the previous ones. The child is then given one chromosome from each pair and the other is discarded. This happens in both parents so that the child receives one full set of chromosomes from each parent. | ||
== Y | == Sex Chromosomes (X and Y) == | ||
[https://isogg.org/wiki/Y_chromosome_DNA_tests | [https://isogg.org/wiki/Y_chromosome_DNA_tests Sex Chromosomes]: There are 22 pairs of autosomal DNA. The 23rd and final pair are the sex chromosomes which come in two variants, X, and Y. Females have two X chromosomes, and males have an X and a Y. The X chromosome is about as big as chromosome 7 and the Y is about as big as chromosome 21. In other words, the X chromosome is about 3 times bigger than the Y chromosome. Because they are so different in size, during recombination in males, the two try to line up at but can only perform recombination at the tip (in females the two X chromosomes recombine without any problems). The father gives the child all of his X or all of his Y. If he gives X, the child becomes a biological female if he gives Y the child becomes a biological male. Because of this rule, both have unique inheritance patterns. | ||
Y-DNA: The Y chromosome is only passed down father to son and only males have a Y chromosome. The Y chromosome does not go through the recombination process so the only way it can change is through spontaneous mutations. These mutations are usually harmless and the only way you can know if you have one is by taking a Y-DNA test. | |||
Y-DNA has several advantages for genetic genealogists. It mutates at a faster rate than mtDNA and at a rate that is more useful for genealogists. By comparing the Y-DNA of two individuals it is possible to determine how closely the two are related on the direct male line. Anyone who matches your Y-DNA test is related on both your and their direct paternal line. The common ancestor will always be a man who had at least two sons, one of which you descend from and the other that the match descends from. Because Y-DNA can only change through mutations, it can be used to find relatives on the direct male line up to 25 generations back whereas autosomal DNA is usually only helpful up to about 5 generations back. Because Y-DNA and surnames are usually both passed down father to son, Y-DNA surname projects exist that try discover how everyone with the same surname is related. Such projects can be less effective with common names like Smith, but can be extremely effective with unique surnames like Tolman. | |||
The biggest disadvantage to Y-DNA research is far less people have taken Y-DNA tests than they have autosomal DNA tests. The only way to overcome this obstacle is for more people to test. The other disadvantage is that Y-DNA can only reveal information about your direct male line. If you wanted to use Y-DNA to research your mother's father's surname, for example, your Y-DNA would not work. You would need to test your maternal grandfather or another close relative related on the direct male line. | |||
== Mitochondrial DNA == | == Mitochondrial DNA == | ||