Question

Write notes on the following: (i) Chromosomal aberrations (ii) Pedigree analysis.

Hint:

One note is about changes to chromosome structure or number; the other is about reading inheritance patterns from a family tree.

Answer 1

Step 1: Chromosomal aberrations, what they are.
Chromosomal aberrations are changes in the normal structure or number of chromosomes, different from a simple gene mutation, which only changes one small DNA sequence.

Step 2: Chromosomal aberrations, types.
Structural aberrations include deletion (part of a chromosome is lost), duplication (a segment is repeated), inversion (a segment is reversed), and translocation (a segment moves to a different chromosome). Numerical aberrations, called aneuploidy, involve gain or loss of individual chromosomes, as seen in Down's syndrome, where an extra copy of chromosome 21 is present (trisomy 21).

Step 3: Pedigree analysis, what it is.
Pedigree analysis is the study of a family's history of a particular trait or disorder across several generations, recorded using a standard chart of symbols, to work out how that trait is being inherited.

Step 4: Pedigree analysis, its use.
By tracing which family members show a trait, geneticists can tell whether the trait is dominant or recessive, and whether the gene is autosomal or sex linked, which is valuable for genetic counselling of families.

Final Answer:
Chromosomal aberrations are structural or numerical changes to chromosomes (like trisomy 21 in Down's syndrome); pedigree analysis traces a trait through a family tree to work out its pattern of inheritance.