Haemophilia is caused due to lack of

Experimental verification of the chromosomal theory of inheritance was given by

Heterozygous round and yellow seeded pea plants were selfed and total $800$ seeds are collected. What is the total number of seeds with first dominant and second recessive traits?

$A$ : Myotonic dystrophy is caused by recessive mutant pleiotropic gene.
$R$ : Gene mutation leads to more synthesis of fibrillin proteins.

Mongolism syndrome is caused by