. Journal of radiology . orhybridized with other similarly derivedheterozygous greys, will give the samethree types, dominant greys, heterozy-gous greys, and recessive albinos. Again, if we cross a dominant greywith a heterozygous grey, the firsthybrid generation will give dominantgreys and heterozygous grevs in theproportion of one to one. The domi-nant greys will breed true, and theheterozygous greys will again give thesame three types. Why do these characters behave inthis way? That they do is is the secret of the method ofheredity? If we mate two purebredalbinos the offspring
. Journal of radiology . orhybridized with other similarly derivedheterozygous greys, will give the samethree types, dominant greys, heterozy-gous greys, and recessive albinos. Again, if we cross a dominant greywith a heterozygous grey, the firsthybrid generation will give dominantgreys and heterozygous grevs in theproportion of one to one. The domi-nant greys will breed true, and theheterozygous greys will again give thesame three types. Why do these characters behave inthis way? That they do is is the secret of the method ofheredity? If we mate two purebredalbinos the offspring will all be albino;that is, there will be a complete lackof the pigment-making mechanism. Pig-ment is an absent character in theseindividuals. It did not go into theirgerm plasm and they cannot transmitit to their offspring. If only albino miceare allowed to breed, the pigment-mak-ing mechanism will be lost for mice andcannot be recovered, and there will 455 INHERIT ABILITY OP SPONTANEOUS CANCER SLYE PAFCT Of STRAIN 5 5. thereafter be only albino mice. Albin-ism is a recessive character. Purebredalbinos cannot transmit the dominant. Now, if we mate the same pure-bred albino, into whose germ plasm nopigment-making mechanism went, witha grey house mouse into whose germplasm the tendency to pigment-makingmechanism did go, we shall get in thefirst hybrid generation, heterozygousgreys, that is, pigment-making is domi-nant over the lack of pigment-making,therefore the mice are grey. But intotheir germ plasm went from one sidethe absence of the pigment-makingmechanism (as a unit character), andfrom the other side went the presenceof the pigment-making mechanism (an-other unit character) ; so, since boththese unit characters went into theirgerm plasm, both of these characterswill come out somewhere in the off-spring—the law of heredity. All efficient study of heredity is thestudy of the behavior of unit we must be sure that we haveanalyzed our characteristics into uni
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