$A$ human with $45$ chromosomes having only one $X$ chromosome $(XO)$ suffers from which of the following disorders?

- Physical, psychomotor and mental development is retarded.
- Palm is broad with characteristic palm crease, these symptoms show....

In humans,which disorder is caused due to the absence of one of the $X$ chromosomes,i.e.,$45$ with $XO$?

Three copies of chromosome-$21$ in a child with Down's syndrome have been analysed using molecular biology technology to detect any possible $DNA$ polymorphism with reference to different alleles located on chromosome-$21$. Results showed that out of $3$ copies,$2$ of the chromosomes of the child contain the same alleles as one of the mother's alleles. Based on this,when did the non-disjunction event most likely occur?

In humans,mental retardation is associated with sex-linked abnormalities. It is generally due to:

Which chromosomal aberration does the following figure indicate?