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DNA chromosomes look like long twisty ladders. The longest chromosome (1) has over 249 million rungs and the smallest (21) has over 48 million. In total there are over 3 billion of these rungs in human DNA. Each rung in the ladder will contain a pair of nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). A and T are always paired together and C and G are paired together. Although two SNPs will always be together at each spot, only one of the two values at each spot will do any coding, the other is just a backbone that holds the structure together. The side that does the coding is called the + strand and the side that is the backbone is the - strand. Sometimes in an A T pair, the A will be the coding gene and the T will be the backbone, other times it will be the reverse and the same is true for C and G pairs. For simplicity, DNA companies will therefore just record the value of a person's + strand at each spot they test.
DNA chromosomes look like long twisty ladders. The longest chromosome (1) has over 249 million rungs and the smallest (21) has over 48 million. In total there are over 3 billion of these rungs in human DNA. Each rung in the ladder will contain a pair of nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). A and T are always paired together and C and G are paired together. Although two SNPs will always be together at each spot, only one of the two values at each spot will do any coding, the other is just a backbone that holds the structure together. The side that does the coding is called the + strand and the side that is the backbone is the - strand. Sometimes in an A T pair, the A will be the coding gene and the T will be the backbone, other times it will be the reverse and the same is true for C and G pairs. For simplicity, DNA companies will therefore just record the value of a person's + strand at each spot they test.


== Single-nucleotide polymorphisms (SNPs) ==
== Single-nucleotide polymorphisms (SNPs) ==
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All human beings are 99.9% identical in their genetic makeup meaning that at out of the 3 billion genes we all have 99.9% are the same in all humans. The places where it is possible for a variance to occur are called, SNP's which stands for Single-nucleotide polymorphisms. SNP's are the main force behind DNA and what gives it it's genealogical value. When two individuals have enough matching SNP's in a row, this becomes a matching segment. The more matching SNP's there are, the bigger the segment is. If a segment is big enough (bigger than 15cm's), it is safe to assume the two individuals share that segment because they both descend from a common ancestor who passed on that segment of DNA to both testers. The more matching segments there and the bigger they are, the closer two test takers are probably related. By testing a sample of a person's SNP's and then comparing them to everyone else in the database, it is possible to identify a person's genetic relatives. Most major companies will test 500-600k SNP's.
All human beings are 99.9% identical in their genetic makeup meaning that at out of the 3 billion genes we all have 99.9% are the same in all humans. The places where it is possible for a variance to occur are called, SNP's which stands for Single-nucleotide polymorphisms. SNP's are the main force behind DNA and what gives it it's genealogical value. When two individuals have enough matching SNP's in a row, this becomes a matching segment. The more matching SNP's there are, the bigger the segment is. If a segment is big enough (bigger than 15cm's), it is safe to assume the two individuals share that segment because they both descend from a common ancestor who passed on that segment of DNA to both testers. The more matching segments there and the bigger they are, the closer two test takers are probably related. By testing a sample of a person's SNP's and then comparing them to everyone else in the database, it is possible to identify a person's genetic relatives. Most major companies will test 500-600k SNP's.


== Types of DNA ==
== Autosomal DNA ==
 
[[File:Morgan crossover 1.jpg|thumb|right|350px|<center>Autosomal Recombination/center>]]
 
Autosomal DNA (atDNA): This makes up about 95% of human DNA. It consists of 22 pairs of chromosomes and in each pair, one is from mom and one is from dad. The pairs of chromosomes are simply names 1, 2, 3, etc... 21, 22. They are mostly named by their size with chromosome 1 being the largest, chromosome 2 being the second largest etc. They are not perfectly named by their size, for example chromosome 22 is actually bigger than chromosome 21, chromosome 20 is slightly bigger than chromosome 19 etc. This is because as our understanding of DNA grows and improves, some chromosomes turned out to be a little bigger or smaller than we initially thought.
 
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.


*Autosomal DNA (atDNA): This makes up about 95% of human DNA. It consists of 22 pairs of chromosomes and in each pair, one is from mom and one is from dad. The pairs of chromosomes are simply names 1, 2, 3, etc... 21, 22. They are mostly named by their size with chromosome 1 being the largest, chromosome 2 being the second largest etc. They are not perfectly named by their size, for example chromosome 22 is actually bigger than chromosome 21, chromosome 20 is slightly bigger than chromosome 19 etc. This is because as our understanding of DNA grows and improves, some chromosomes turned out to be a little bigger or smaller than we initially thought.
== Y-DNA ==


It is the most important and most commonly tested type of DNA. A child will have exactly half of their autosomal DNA from each parent.
[https://isogg.org/wiki/Y_chromosome_DNA_tests Y-DNA]: The term Y-DNA refers to the Y-Chromosome. 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. This is the second most valuable type of DNA. Although females do not have Y-DNA, they can get the same information by testing a close male relative such as a father or brother.
*[https://isogg.org/wiki/Y_chromosome_DNA_tests Y-DNA]: Only males have Y-DNA and it is passed down father to son. This is the second most valuable type of DNA. Although females do not have Y-DNA, they can get the same information by testing a close male relative such as a father or brother.
*Mitochondial DNA (mtDNA): The smallest portion of human DNA. MtDNA exists in males and females, but is only inherited from the mother. MtDNA is important but overall is the least valuable type of DNA.
*Mitochondial DNA (mtDNA): The smallest portion of human DNA. MtDNA exists in males and females, but is only inherited from the mother. MtDNA is important but overall is the least valuable type of DNA.


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