Show the epistatic relationship of the following genes involved in sex-determina
ID: 63573 • Letter: S
Question
Show the epistatic relationship of the following genes involved in sex-determination in C. elgans based upon their single- and double- homozygous mutant phenotypes. Single-homozygous mutant phenotypes are on the diagonal, double-homozygous mutant phenotypes are above the diagonal.
sdc-1
tra-1
tra-2
her-1
fern-1
xol-1
sdc-1
male
male
male
female
female
male
tra-1
male
male
male
male
male
tra-2
male
male
female
male
her-1
female
female
female
fern-1
female
female
xol-1
female
sdc-1
tra-1
tra-2
her-1
fern-1
xol-1
sdc-1
male
male
male
female
female
male
tra-1
male
male
male
male
male
tra-2
male
male
female
male
her-1
female
female
female
fern-1
female
female
xol-1
female
Explanation / Answer
Ans : The epistatic relationship of the following genes involved in sex-determination in C. elgans based upon their single- and double- homozygous mutant phenotypes the relationship is mentioned below :
Because sex-determination mutants have been investigated extensively the genes can be ranked in a hierarchy of epistasis, in the order her-1 < tra-1, tra-2 < fem-1, < tra-1,< xol-1 in respect of somatic phenotype Thus, in somatic tissues, recessive (masculinizing) mutations of tra-1 are epistatic to all feminizing mutations of her-1, fem-1, and so forth. A slightly different situation is found with regard to germ-line phenotype, for which the hierarchy of epistasis has the order her-1 < tra-2, < tra-1 < fem-1 < xol-1. Consequently, fem(O) mutations are epistatic to tra-l(O) in the germ line but not in the soma, so that the double mutant tra-1 (0);fem-1 (0) has an entirely male body and gonad morphology, but its germ line makes oocytes rather than sperm.
The epistatic interactions so far identified provide some evidence for the patterns of gene activity
(1) In the XX soma: high X/A ratio represses her-1; therefore, tra-1 and tra-2 are active. These gene activities repress the three fern genes; therefore, tra-1 is derepressed, and female somatic development ensues.
(2) In the XX germ line, high X/A ratio represses her-1; therefore, tra-1 and tra-2 should be derepressed.
(3) In the XO soma and germ line, low X /A ratio activates her-1; therefore tra-2 and tra-3 are repressed.
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