All dogs, as well as every other type of animal and plant living on Earth, are made up of living cells. Each one of these microscopic "building blocks of life" contains a specific set of "biochemical blueprints" called chromosomes. These complex molecules not only make it possible for cells to repair and reproduce themselves, but they also "instruct" the cell what it's function is. For example, whether a cell is supposed to be part of an organ like the heart, or part of your skin, or if it's role is to grow a hair on top of your head.
Chromosomes themselves are made up of small building blocks called genes, each of which is responsible for influencing a single function, or trait, in that cell. When paired along the two strands of a chromosome, genes act in one of two ways. One way genes can act is in an "additive" manner (i.e., the genes are either identical in form & function, and therefore produce the same trait, OR they are different but are capable of combining in a manner that produces a modified form, or hybridization, of the two traits). The second way paired genes act is when one gene is dominant and the second gene is recessive: only the trait of the dominant gene is carried out, or expressed, in (or by) the cell. The recessive gene's trait is masked by that of the dominant gene, but is still present on the chromosome.
When plants and animals "have babies", each offspring is created from the joining of one strand (= half) of each of the "father's" chromosomes with one strand from each of the "mother's" chromosomes. This creates an opportunity for each gene along corresponding chromosome strands to be paired up with a corresponding gene that has a different trait variation from what it was paired with before, possibly causing the resulting offspring to have many different trait-characteristics from its parents. By the same token, an offspring's chromosomes may end up being nearly identical to one or both of the parents'.
People found out long, long ago that many traits... such as the hair color of dogs... could be "manipulated" to produce new colors (or do away with other colors) by breeding dogs that have one particular coat color to others. A British mathematician/biologist named R.C. Punnett developed a straight-forward yet powerful statistical tool called the Punnett Square to predict the outcome/offspring of breeding individuals with known traits for various characteristics. Below is an example of a Punnett Square that was created to determine the coat color outcome in the litter of puppies produced if two cocker spaniels with black hair are bred. Each parent dog has at least one parent or grandparent that has buff (= blonde) hair. Since hair color is expressed by a pair of genes on a chromosome, let's represent the gene for black hair with the capital letter B (since black tends to be a dominant color) and the gene for buff hair with the lower-case letter b (since buff/blonde tends to be a recessive color). This breeding, or "crossing", can thus be represented mathematically by the equation Bb x Bb, since each parent dog is black (B) but has buff (b) in its recent background. The Punnett Square is used to predict the outcome of this gene crossing by placing one of the female parent's two gene letters in the pink box above each of the two columns of the Punnett Square table, and then placing each of the male parent's gene letters in the blue box to the left of each of the two rows of the table. Next, starting with the first row of the table, pair the letter which corresponds for that row (B) with the letter that corresponds with each column, and fill in each new gene pair (of letters) in the corresponding box for each row-column match up. Repeat this step for the second row (which corresponds with the letter b). The resulting four pairs of letters (gene pairs) in the Punnett Square table represent (in this example) the predicted proportions of the puppy litter that will have a particular coat hair color : |
|
