“…Since Erba, IL-3, and CSA were mapped by analysis of somatic cell hybrids, further studies will be needed to determine how close these genes are to one another and to Erbb and Hba. In contrast to the apparent clustering of these genes on the mouse chromosome, in humans c-erb-A, c-erb-B, and Hba are reported to be on three different chromosomes (13,19), whereas CSA and IL- 3 have not yet been mapped. Therefore, it is unclear whether the physical association of Hba, Erba, Erbb, CSA, and IL-3 on the mouse chromosome has some functional or evolutionary significance or is merely fortuitous.…”