9. Direct correlation between recombination frequency and distance between genes can be disturbed by presence of
(1) Heterochromatin       (2) Exons
(3) Introns                   (4) Euchromatin

Introduction:
In genetics, recombination frequency is commonly used to estimate the physical distance between genes on a chromosome. Typically, there is a direct correlation where recombination frequency increases with the distance between genes. However, this relationship can be disturbed by various chromatin structures. Understanding these factors is crucial for accurate genetic mapping and linkage analysis.

Explanation of Options:

1. Heterochromatin:
   Heterochromatin is a densely packed form of chromatin that is transcriptionally inactive and often found in regions like centromeres and telomeres. It acts as a physical barrier to recombination due to its compact structure, reducing crossover events in these regions. This disruption leads to an underestimation of the actual physical distances between genes located in or near heterochromatin, thereby disturbing the direct correlation between recombination frequency and gene distance.

2. Exons:
   Exons are coding sequences within genes that are expressed in the final mRNA product. Exons themselves do not affect recombination frequency directly as they are part of the gene’s functional sequence rather than influencing chromatin structure or crossover mechanisms.

3. Introns:
   Introns are non-coding sequences within genes that are spliced out during mRNA processing. Similar to exons, introns do not directly influence the recombination frequency or its relationship with gene distance since their presence does not alter chromatin compaction or crossover likelihood.

4. Euchromatin:
   Euchromatin is a loosely packed form of chromatin associated with actively transcribed genes. It facilitates recombination by allowing greater accessibility to the recombination machinery. Thus, euchromatin generally supports the direct correlation between recombination frequency and distance because it does not pose a barrier like heterochromatin does.

This detailed understanding clarifies that among the options, only heterochromatin significantly disturbs the direct correlation between recombination frequency and gene distance due to its compacted and repressive chromatin structure affecting crossover rates.