Figure 3. Tetrad analysis of histone deletions. (A) The relevant features
of a cross between the copy-I deletion strain MSY155 and the
copy-II deletion strain MSY158 are shown. Two linkage groups are
illustrated in each "cell" representing the unlinked copy-I and copy-
II histone H3-H4 loci. The deletions are represented by the open
triangles on each linkage group. The cross results in a diploid that
ishemizygous for each H3-H4 gene set. (B) The segregation results
expected for the cross are shown for each class of tetrad. If at least
one copy of either set of histone H3 and H4 genes is essential, then
thetetrad analysis will show a pattern in which spores inheriting
both gene deletions will be dead. That is, tetrads giving two live
and two dead spores should be nonparentalditype, those giving
three live spores and one dead should be tetratype, and those giving
four live spores should be parental ditype.