Not something that is contained in a will, but rather a gene, chromomsome or genome that is transmitted from parent to child. The pattern of inheritance is the manner in which a gene is transmitted. For example, the pattern of inheritance may be as a trait that is transmitted from father or mother to son or daughter such as height or eye colour.
With the union of the egg and sperm, the individual begins life with a mixture ( admixture ) of the Autosomal DNA from both parents. This admixture is not a pure 50%-50%. It will vary from child to child and is the determining factor for the differences among siblings. Identical twins share identical DNA where fraternal twins do not share identical DNA. The Y chromomsome is only received by the son only from his father and both sons and daughters receive their mtDNA only from their mothers.
To understand the possible inheritance of genetic traits let's consider the following:
are a complex inheritance process.
2. The exact mixture of chromomsome mixture at conception varies and does not follow a simple formula.
3. Y-DNA and mtDNA DNA are different than the other autosomal DNA. They both are not a mixture from either parent, but supplied by only one parent.
4. The X-chromosome for the male comes directly from his mother, his Y-chromosome comes directly from his father. The X-chromosomes for a female are an admixture of her father's X-chromosome and her mother's X-chromosomes on average about 50% from each. This admixture is what makes siblings different. Identical twins share the same DNA admixture, but all the rules above still apply.
Ok, what does this mean for genealogy and genetics. The actual markers chosen for genealogical genetics are the relatively stable and uniquely inherited DNA. Y- chromomsomes are only inherited from father to son and have very slow mutation rates. mtDNA is inherited by both sexes only from their mothers. mtDNA is even less prone to mutation than Y-DNA.