DNA Basics Chapter 4: A Glossary of Terms

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We’ve covered quite a few concepts in the DNA Basics series so far. Here is a glossary of terms both as a review, and as a helpful reference for understanding future chapters. If there are additional terms you think should be included, please let me know in the comments!

Allele: The A, T, G, or C you inherited from each parent for a given genetic marker

Amino acids: The building blocks of proteins

Centimorgans (cM): a measure of the distance between two positions on a chromosome in which the chromosome is expected to “break” and then recombine with the other chromosome in the pair before being passed on, an average of 0.01 times each generation

Every generation, the two chromosomes within each chromosome pair, “break” and recombine, “swapping” pieces with each other, before being passed down. So when a child inherits a chromosome 7 from his father, he is not inheriting the same chromosome 7 his father inherited from his father, or the chromosome 7 his father inherited from his mother; rather, the child inherits one chromosome 7 from his father that is a combination of his paternal grandparents’ chromosome 7s.

Schematic representation of chromosome recombination

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cM is not a physical distance: two segments that are both 10cM could each include a different number of base pairs, i.e., one segment could be longer than the other, even though both are 10cM because both have the same likelihood of recombining.

Chromosome: The “bundles” of DNA that are passed down from parent to child. There are 23 pairs of chromosomes — one chromosome in each pair is inherited from each parent. 22 chromosome pairs are autosomal; the last pair consists of the sex chromosomes, X and Y.

Chromosome Browser: A tool that maps a person’s chromosomes graphically. Essentially it is used to visualize shared DNA segments that people who share DNA have in common.

Codon: A sequence of three nucleotides that corresponds with a specific amino acid (or stop signal) during protein synthesis

DNA: Short for deoxyribonucleic acid, DNA is the molecule that carries the genetic instructions for every living thing, including people; it is made up of a sequence of nucleotides

DNA Matches: These are people who are likely to be your relatives (close or distant) because there are significant similarities between their DNA and yours.

By comparing the DNA of the more than 1 million people in the MyHeritage DNA database, we are able to find DNA Matches and show information about the match: the estimated relationship between you and the DNA Match, the amount of shared DNA you have in common, the number of shared DNA segments, and the size of the largest of the shared DNA segments.

Example of a DNA Match

DNA sample: A specimen that includes some of your DNA.

Because your DNA is essentially the same in all of the nuclei in your body, analyzing DNA from a nucleus from any cell will be representative of your DNA sequence everywhere. When you take a MyHeritage DNA test, you swab the inside of your cheeks which removes some epithelial cells that get stuck to the swab. When we receive your sample in the lab, we extract the DNA from the cells and analyze it.

Ethnicity Estimate: A percentage breakdown of your ancestral background

Because years ago the vast majority of people married other people from the same region, and had children who then married in the same region, a correlation can be seen between DNA and geographic location (and certain endogamous cultural groups). When we compare your DNA to models of DNA from different ethnicities, we can tell you how much of your DNA was likely inherited from each of the 42 ethnicities we compare it to

Founder population: Founder populations are people whose ancestors lived in the same region of the world for generations, so that their DNA is highly characteristic of the region. By testing the DNA of the participants in the project, MyHeritage established profiles for each region that reflect its unique DNA sequences.

Gamete: A sex cell — egg in women and sperm in men — that have only one of each chromosome, not a pair of each chromosome. When two gametes fuse during fertilization, the resultant cell then has 23 chromosome pairs.

Gene expression: The process of a section of DNA being transcribed to RNA, and then translated to protein.

Genes: Sections of DNA that are transcribed into RNA and then translated into proteins. Genes make up about 1–2% of our DNA; the rest does not code for proteins.

Genetic marker: Sections of DNA that vary between people/

Genomic location: Where on a chromosome a certain genetic marker, or DNA segment, or other element is located.

When hovering over any shared DNA segment in the MyHeritage Chromosome Browser, you will see the genomic location of the segment. “Genomic position” indicates the first and last base pair, or nucleotide, of the segment, counting from the end of the chromosome. RSID stands for Reference SNP ID and indicates the “name” of the first and last SNPs of the segment.

Example of the information that appears when hovering over a triangulated segment in the Chromosome Browser

Genotype: The combination of two alleles — one of which was inherited from each of your parents — for a specific genetic marker

Inherited by descent (IBD): A matching segment of DNA shared by two or more people that they inherited from a common ancestor

Imputation: A computational technique used to infer DNA sequences that were not read; akin to reading a sentence with some of the letters missing — there’s a good chance that you can infer the missing letters from context. Not all DNA service providers read the same SNPs. To find DNA Matches for individuals who used different DNA service providers, it is important to infer the SNPs that were not read before comparing results.

Nucleotides: The building blocks of DNA (A, T, G and C) and RNA (A, U, G and C)

Phenotype: A genetic trait that is partially determined by a genotype. For example, if your genotype is AA (an A was inherited at that position from both parents), this might mean your hair color phenotype is brown.

Precision and recall: The accuracy of estimating a relationship of a DNA Match is measured using two parameters called recall and precision. Perfect accuracy means, in part, suggesting the correct relationship for every DNA Match (recall) and not proposing too wide a range of possible relationships in order to make sure the correct relationship is included (precision).

Protein: Made up of amino acids, proteins do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.

RNA: Short for ribonucleic acid. DNA is transcribed into RNA in the process of gene expression.

Single nucleotide polymorphisms (SNPs): One type of variation between people’s DNA sequences, that is one-nucleotide long.

Transcription: The process of DNA being copied into RNA

Translation: The process of proteins being synthesized based on RNA sequences

Zygote: The cell that results from two gametes fusing in fertilization

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