Page:Popular Science Monthly Volume 62.djvu/279

From Wikisource
Jump to: navigation, search
This page has been proofread, but needs to be validated.

(except in a single individual). Hence the cross VB X GS gives us the hybrid VgSb. When this hybrid produces pollen and ovules, the pair of characters V and G separate, V going to half the pollen grains and ovules, and G to the other half. S and B do the same thing, but without reference to V and G. Hence we have four kinds of pollen grains and four of ovules, as shown in the following diagram:

Pollen. Ovules.
VB VgSb VB VB Here we have a mixture of four kinds of pollen offered to four kinds of ovules. On the average, one fourth of each kind of ovules will be fertilized by each kind of pollen, giving sixteen equally numerous fertilizations, as follows:
1. VB VB VB. 9. VB GB VgB.
2. VS VB VSb. 10. VS GB VgSB.
3. GB VB VgB. 11. GB GB GB.
4. GS VB VgSb. 12. GS GB GSb.
5. VB VS VSb. 13. VB GS VgSB.
6. VS VS VS. 14. VS GS VgS.
7. GB VS VgSb. 15. GB GS GSb.
8. GS VS VgS. 16. GS GS GS.

Here it will be noticed that (2) and (5) give the same result. Similarly, (3) and (9); (8) and (14); (12) and (15); and (4), (7), (10) and (13). We may, therefore, represent the hybrid and its progeny thus:

VgSb 1 VS This diagram may easily be extended to later generations. VS will produce VS. The progeny of the type VSb will all have the character V, but one fourth of it will have the character S, two fourths Sb, and one fourth B; thus,
2 VSb
1 VB
2 VgS
4 VgSb
2 VgB
1 GS
1 GB
16 parts
VSb 1 VS
2 VSb
1 VB
4 parts.

In like manner the progeny of the other types may be written out.

Of the nine types produced from the hybrid, four of them, VS, VB, GS, GB, are pure, and will reproduce true to seed. They have no characters hidden in them to crop out in later generations. It will be noticed that each of these pure types constitute one sixteenth of the progeny of the hybrid. Four other types, VSb, VgS, VgB