1. Additional data on the location of Dt.
In the News Letter of March 5, 1940, backcross linkage data for Dt and Wx and F2 data for Dt and Sh were given. These data showed 41 percent recombination between Dt and Wx and 27 percent between Dt and Sh. The order apparently was Dt Sh Wx and the recombination value with Sh indicated that Dt should fall close to Yg2 near the end of the short arm of chromosome 9. The following data on the location of Dt were obtained this past year.
| Dt Sh | x | dt sh | gave | Dt Sh | Dt sh | dt Sh | dt sh | Total |
| dt sh | 617 | 266 | 305 | 588 | 1776 |
Dt Sh - 32 percent recombination
| Dt Yg Wx | selfed |
| dt yg wx |
| Dt Yg Wx | - | 1450 | dt yg Wx | - | 385 | |
| Dt yg wx | - | 38 | dt Yg Wx | - | 223 | |
| Dt Yg wx | - | 360 | dt Yg wx | - | 63 | |
| Dt yg Wx | - | 36 | dt yg wx | - | 238 | |
| Total 2793 | ||||||
| Recombination values: |
Dt Yg 11 % |
| Dt Wx 42 % | |
| Yg Wx 37 % |
| Dt Yg Sh Wx | selfed |
| dt yg sh wx |
| Dt Yg Sh Wx | - | 387 | dt Yg Sh Wx | - | 52 | |
| Dt yg Sh Wx | - | 7 | dt yg Sh Wx | - | 84 | |
| Dt Yg Sh wx | - | 59 | dt Yg sh Wx | - | 2 | |
| Dt yg Sh wx | - | 2 | dt yg sh Wx | - | 49 | |
| Dt Yg sh wx | - | 35 | dt Yg Sh wx | - | 1 | |
| Dt yg sh wx | - | 10 | dt yg Sh wx | - | 3 | |
| Dt Yg sh Wx | - | 15 | dt Yg sh wx | - | 9 | |
| Dt yg sh Wx | - | 3 | dt yg sh wx | - | 61 | |
| Total : 779 | ||||||
| Recombination values: |
Dt Yg 10 % |
| Dt Sh 27 % | |
| Dt Wx 44 % | |
| Yg Sh 24 % | |
| Yg Wx 38 % | |
| Sh Wx 20 % |
These data indicate that the order is Dt Yg Sh Wx and they place Dt ten units beyond Yg. Creighton found only one percent recombination between Yg and the terminal knob on the short arm of 9 so there is some discrepancy here. It should be noted that in selfing a Dt dt plant three classes of seed are obtained, i.e. the Dt Dt Dt, the Dt Dt dt and the Dt dt dt classes. In this latter class possessing a single Dt allele the mutation rate is so low that a considerable number of Dt dt dt seeds were classified as dt because no dots (mutations) are evident. This fact introduces some error into the recombination values but nevertheless the order should be as indicated. The locus of Dt therefore lies beyond Yg and must be very near the end of the short arm of chromosome 9.