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OK, I am being nit picky, but not exactly correct. The pea comb gene and the blue eggshell gene are very closely linked, meaning that about 97% of the time these genes are inherited from one chromosome; about 3% of the time one gene is inherited from one chromosome and the other gene from the other chromosome.
Also, there are many breeds with pea combs that do not carry the blue eggshell gene--for these breeds you could say that the not-blue eggshell gene is closely linked. However, if you breed a pea combed blue eggshell bird with a pea comb not-blue eggshell bird (such as a brahma), all will be pure for pea comb, but will be het for blue eggshell. About half of THEIR offspring will inherit pea comb and not-blue eggshell--originating from their not-blue eggshell grandparent (brahma).