True-breeding is observed when parents pass certain phenotypic traits to offspring and are homozygous for every trait. As B is black and b is white, the genotypes of parental dogs should be BB and bb. According to Mendelian laws, the possible offspring are:
Parents: BB (black) × bb (white)--> offspring: BB (black), 2Bb (black) and bb (white).
In this case, the expected phenotypic ratio of the offspring is:
3 black : 1 white.
As the total number of produced dogs is 1204, the expected phenotypic ratio is:
903 black : 301 white
In the breedin example, the observed phenotypic ratio of the offspring:
922 black : 282 white
According to chi-square equation:
X2 = (observedblack - expectedblack)2 / expectedblack + (observedwhite - expectedwhite)2 / expectedwhite = (922 - 903)2 / 903 + (282 - 301)2 / 301 = 0.4 + 1.2 = 1.6
As there are two phenotypic classes, the number of degrees of freedom (df) equals 2 -1 = 1.
As X2 = 1.6 and df = 1, p-value = 0.2
As 0.2 > 0.05, the null hypothesis is accepted. As a result, there is no difference between the expected and observed numbers of produced dogs. Therefore, the coat color in long-haired labs is inherited in a Mendelian fashion.