Figure 3.
Conditions for an X-linked gene drive construct to spread into a population or induce a population crash. A: Strong condition for allele fixation. An X-linked construct is expected to spread to allele fixation, even in the presence of modest fitness costs, if XtY or XTXt offspring of crosses between XTY males and XTXt females are rendered unviable (c7= 0 and/or c11= 0, red line), or if XTXt offspring of crosses between XtY males and XTXT females are unviable (c9= 0, red line). Another requirement is that crosses between XTY males and XTXT females produce at least partially viable female and male offspring (c1, c3 > 0, green ovals). B: An example of a construct that satisfies this condition is shown (c7, c9, c11= 0). C: Weak condition for allele fixation. An X-linked construct that does not satisfy the strong condition for allele fixation (c7, c9, c11, = 1, green ovals) can still spread to allele fixation, in the absence of a fitness cost, if the number of t alleles among unviable offspring (candidate offspring having one or more t allele are crossed with red lines) equals or exceeds the number of T alleles among unviable offspring of crosses between XTY males and XTXt females and between XtY males and XTXT females. The one exception is that offspring of XtXt females are not counted if XtXt offspring are unviable themselves (Equation 27). Crosses between XTY males and XTXT females must also produce at least partially viable female and male offspring (c1, c3 > 0, green ovals). D: An example of a construct that satisfies this condition is shown (c10, c13, c14, = 0). E: There are several ways in which an X-linked construct can induce a population crash, most of which result in an all female population. The following construct provides one example (c3, c7, c9, c11, c13, c14= 0). F: Beginning from a 60% release proportion, the construct fixes and induces an all-female population crash within 12 generations.