Biology Reference
In-Depth Information
FIGURE 18.9
Inheritance of wBruAus. (A) Cross between wBruAus-bearing (COA) males and wBruAus-
free (CO) females. (B) Cross between wBruAus-free (CO) males and wBruAus-bearing (COA) females. Shade
indicates presence of wBruAus. The inheritance patterns are in agreement with X-linked inheritance. Sex
chromosome types deduced are shown in rectangles. X
A
means the X chromosome carrying wBruAus.
Numbers beneath the rectangles are the number of offspring obtained. [From Kondo, N., Nikoh, N., Ijichi,
N., Shimada, M., and Fukatsu, T. (2002b).
Proc. Natl. Acad. Sci. U.S.A.
99:
14280Ï14285.]
with CO males, wBruAus exhibited 1:1 segregation in both males and females (Figure 18.9A). The
crosses between CO fathers and COA mothers produced all COA offspring, superÝcially showing
typical maternal inheritance. However, when the COA female offspring were mated with CO males,
wBruAus did not exhibit maternal inheritance but 1:1 segregation in both males and females (Figure
18.9B). Notably, all these patterns were perfectly explained by the sex-linked inheritance in male-
heterozygotic organisms (Figure 18.9), which agreed with the karyotype of
C. chinensis
(2
n
= 20,
XY) (Takenouchi, 1955; Figure 18.10).
SEX-DEPENDENT DENSITY DIFFERENCE OF
W
B
RU
A
US
Based on the antibiotic insensitivity and the sex-linked inheritance, it was suggested that perhaps
wBruAus had no microbial entity but was a bacterial genome fragment associated with X chromo-
A
B
FIGURE 18.10
Chromosome specimens of
C. chinensis
prepared from testes of adult males. (A) Metaphase
of Ýrst meiotic division. Condensed chromosomes (2
n
= 20) are seen. Arrow indicates the highly condensed
Y chromosome. (B) Second meiotic division. Two segregating haploid chromosome sets (
n
= 10 for each)
are seen. Takenouchi (1955) reported the karyotype of
C. chinensis
as 2
n
= 20, XO. However, our Þuorescent
imaging with DAPI revealed a small Y chromosome in males, indicating that the karyotype was 2
n
= 20, XY.
