Maternal inheritance V/S Predetermination 

• Maternal inheritance : Inheritance of some traits of mother to the offspring through the cytoplasm of female gamete. 
• Predetermination : It is the effect of mother's genes on the characters of offspring through the cytoplasm of egg and embryo without involving plasmagenes of cytoplasm. 

Shell coiling in snails 🐌 

There are two types of coiling present in present in snails. 1.Dextral type 2. Sinistral type 

The direction of coiling in shell is controlled by the orientation of mitotic spindle of the first cleavage of zygote. This all depends on the organization of egg before fertilisation. The spindle organisation is controlled by organisation of cytoplasm in the egg. 

• Dextral type : Shell is coiled clockwise (toward right when viewed from apex). It is shown by (DD or Dd) because D is dominant over d. 
• Sinistral type : Shell is coiled anticlockwise. It is shown by dd.
  
  
  

1.Cross between sinistral Female and Dextral male

When eggs of Sinistral female are fertilised with sperms of Dextral male, eggs cleave Sinistrally and F1 snails are Sinistral due to maternal cytoplasmic inheritance through egg.  

When F1 progeny of snails are selfed ,all offspring are Dextral. However, in F3 generation segregation takes place in the ratio of 3:1 .

2.Cross between Dextral male and Sinistral female 
When Dextral female and Sinistral male are crossed  ,all F1 offsprings with genotype (Dd)  are Dextral due to genotype of mother. When F1 are selfed all offspring are Dextral. In F3 segregation takes place in 3:1ratio .