up tend to be
inherited together, i.e., if two or more enter the cross together they tend
to remain together through subsequent generations. On the other hand, any
member of one group is inherited entirely independently of any member of
the other groups; in the same way as Mendel's yellow-green pair of
characters is inherited independently of the round-wrinkled pair.

_Group I_ _Group II_ _Group III_ _Group IV_
Abnormal Antlered Band Bent
Bar Apterous Beaded Eyeless
Bifid Arc Cream III
Bow Balloon Deformed
Cherry Black Dwarf
Chrome Blistered Ebony
Cleft Comma Giant
Club Confluent Kidney
Depressed Cream II Low crossing over
Dot Curved Maroon
Eosin Dachs Peach
Facet Extra vein Pink
Forked Fringed Rough
Furrowed Jaunty Safranin
Fused Limited Sepia
Green Little crossover Sooty
Jaunty Morula Spineless
Lemon Olive Spread
Lethals, 13 Plexus Trident
Miniature Purple Truncate intensifier
Notch Speck Whitehead
Reduplicated Strap White ocelli
Ruby Streak
Rudimentary Trefoil
Sable Truncate
Shifted Vestigial
Short
Skee
Spoon
Spot
Tan
Truncate intensifier
Vermilion
White
Yellow

If the factors for these characters are carried by the chromosomes, then we
should expect that those factors that are carried by the same chromosome
would be inherited together, provided the chromosomes are definite
structures in the cell.

[Illustration: FIG. 52. Chromosomes (diploid) of D. ampelophila. The sex
chromosomes are XX in the female and XY in the male. There are three other
pairs of chromosomes.]

In the chromosome group of Drosophila, (fig. 52) there are _four_ pairs of
chromosomes, three of nearly the same size and one much smaller. Not only
is there agreement between the number of hereditary groups and the number
of the chromosomes, but even the size relations are the same, for there are
three great groups of characters and three pa