Extrachromosomal Inheritan
MATERNAL EFFECTS
, MATERNAL EFFECT - Shell Coiling in Snail
• One of the classical examples of intricate relationship between maternal genotype and egg c
“phenotype” was studied in snails by Sturtevant. He showed that there are two strains of wa
(Limnaea peregra) that differ each other in the direction of coiling of shell.
• Looking into the opening of the shell it can be seen that in one strain the shell always coils t
(sinistral) whereas in the other strain the shell always coils to the right (dextral).
• In the cross dextral female x sinistral male, all the F, progeny have dextral coils implying that
dominant over sinistral. However, in the F1 x F1, cross (i.e., inbreeding), all the F1 snails are also
• The reciprocal cross (dextral male x sinistral female) produces F1, progeny that are all left coil
case F1, x F1, cross also yields only dextral coils.
• From these experiments it becomes clear that coiling of snails is not determined by individu
genes but by those of mother.
MEENU ELIZABATH BENNY
MATERNAL EFFECTS
, MATERNAL EFFECT - Shell Coiling in Snail
• One of the classical examples of intricate relationship between maternal genotype and egg c
“phenotype” was studied in snails by Sturtevant. He showed that there are two strains of wa
(Limnaea peregra) that differ each other in the direction of coiling of shell.
• Looking into the opening of the shell it can be seen that in one strain the shell always coils t
(sinistral) whereas in the other strain the shell always coils to the right (dextral).
• In the cross dextral female x sinistral male, all the F, progeny have dextral coils implying that
dominant over sinistral. However, in the F1 x F1, cross (i.e., inbreeding), all the F1 snails are also
• The reciprocal cross (dextral male x sinistral female) produces F1, progeny that are all left coil
case F1, x F1, cross also yields only dextral coils.
• From these experiments it becomes clear that coiling of snails is not determined by individu
genes but by those of mother.
MEENU ELIZABATH BENNY
