Welcome to the Ron Lindsay Memorial Learning Center
THIS SECTION WILL PROVIDE BASIC CONCEPTS AND LINKS FOR SELF-STUDY.
Ron was committed to life-long learning. He pursued multiple interests via his local chapter of the Osher Lifelong Learning Institute, and he was dedicated to increasing his understanding of genetics and its applications to genealogy. When Ron began Lindsay International nearly two decades ago, he provided many study links so that visitors and regulars could learn along with him. What he digested and assimilated he made available to the Project members via the website. In 2018, there is much out there for self-directed study. Lindsay International will consider it adequate to provide links to useful material, foremost Ron’s favorite DNA links. We will preserve some of his best writings, and provide some elementary tutorials of our own sufficient for the visitor to get an idea of how we are operate.
Lets begin with some introductory genetics in Ron’s own words:
Basic Genetics For The Family Historian
Elementary genetics provides us with the fact that the 23rd chromosome, in the human genome, is the chromosome that determines sex. Males have both an “X” and a “Y” 23rd chromosome, but females only carry an “X” for their 23rd chromosome.
The human egg will becomes a female embryo if the male sperm that initially reaches the egg carries an X-chromosome. The egg will becomes a male embryo if the male sperm that initially reaches the egg carries a Y-chromosome. Thus you can see the Y-chromosome is passed down from generation to generation only through the male line. In order to better understand how we arrived at this point, we need to reach for the next level.
The complete set of instructions for making an organism is called its genome. Found in every nucleus of a person’s many cells, the human genome consists of tightly coiled threads of deoxyribonucleic acid (DNA) and associated protein molecules, organized into structures called chromosomes.
In humans, as in other higher organisms, a DNA molecule consists of two strands that wrap around each other to resemble a twisted ladder whose sides, made of sugar and phosphate molecules, are connected by rungs of nitrogen, containing chemicals called bases. Each strand is a linear arrangement of repeating similar units called nucleotides, which are each composed of one sugar, one phosphate, and a nitrogenous base. Four different bases are present in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). The particular order of the bases arranged along the sugar- phosphate backbone is called the DNA sequence. These sequences specify the exact genetic instructions required to create a particular organism with its own unique traits.
The two DNA strands are held together by weak bonds between the bases on each strand, forming base pairs (bp). Genome size is usually stated as the total number of base pairs. The human genome contains roughly 3 billion base pairs (bp).
These three billion base pairs (bp) in the human genome are organized into 24 distinct, physically separate microscopic units called chromosomes. All genes are arranged linearly along the chromosomes. The nucleus of most human cells contains 2 sets of chromosomes. One set is provided by each parent. Each set has 23 single chromosomes; 22 autosomes and an X or Y sex chromosome. A normal female will have a pair of X chromosomes in this 23rd chromosome; a normal male will have an X and Y pair.
The three blocks below explain three main categories of genetic genealogical investigation. They are presented as very introductory, not in Ron’s words but in the words of his less experienced and less technical successor. This is the shallow end of the pool. Lets get our feet wet.
Y-CHROMOSOME DNA
The Y-chromosome is used for tracing the paternal line. That’s because the Y-chromosome is inherited solely by sons from their fathers. Daughters don’t inherit it. Mothers make no contribution. The son’s Y-chromosome is pretty much identical to that of his father, and his grandfather, etc. Even with random mutations in the Y-chromosome, continuity of signature from father to son can be observed back for thousands of years
Y-DNA is the main line of testing for a Surname DNA Project. That includes ours, the Lindsay Surname DNA Project. There are two sub-categories: STR testing, and SNP testing. These are explained in greater detail elsewhere.
MITOCHONDRIAL DNA
Mitochondrial DNA, similarly, is used for tracing the maternal line. Mitochondrial DNA (mtDNA) is inherited by both sons and daughters, but what they inherit receives no contribution from the father. All of the mtDNA in the sperm cell is is in the tail which gets cast off and left outside the egg when the little swimmer crosses the finish line. Since there’s no contribution from the father, the child’s mtDNA is pretty much identical to the mother’s and the grandmother’s etc, again back thousands of years.
AUTOSOMAL DNA
Autosomal DNA looks at the non-sex chromosomes, the other 22 pairs, which are a shuffling of the DNA of the father and the mother. Half the DNA of each parent, like cutting a deck of cards, gets “shuffled” (recombined) at conception. For the next generation, only a quarter of the DNA from any grandparent gets passed down to a grandchild, etc. While for siblings and close cousins the percentages of inherited DNA are large enough for commonality to be identified, after that it becomes increasingly difficult. Many Autosomal testers have discovered close cousins and even lost siblings of both sexes, but Autosomal DNA’s genealogical utility tapers off rapidly after four generations.
Autosomal testing, often abbreviated au, is the basis for FTDNA’s Family Finder (FF) product.
NOW JUST A LITTLE DEEPER (2 important terms from the glossary):
Short Tandem Repeats (STR): Multiple copies of an identical DNA sequence arranged in direct succession in a particular region of a chromosome. By a sequence is meant a sequence of base pairs. When the DNA helix is unwound it appears as a ladder with rungs (about 60 million of them on the Y-chromosome) which can be thought of as being of four different colors. Think of a base pair as a rung on the ladder, and an STR as a stuttering of a short sequence of rungs.
Single Nucleotide Polymorphism (SNP): A variation in the genetic code at a specific point on the DNA. Some people refer to this as a transcription error. Others think of it as a creative nuance, like introducing a flat or sharp into a musical composition. In the early days of genetic genealogy, the SNPs were used to develop the basic outline of the human family tree at the anthropological level, i.e., before genealogical time. Now, many years on, with the increasing numbers of these variants being discovered and cataloged, they are becoming more relevant for genealogical time.
Recommend Links (Ron's and ours)
Website of the International Society of Genetic Genealogists, particularly their Wiki