18. If bacteria possess two copies of certain genes then they referred as
(1) Amphidiploid      (2) Merodiploid
(3) Euploid              (4) Polyploid

The correct answer for the question “If bacteria possess two copies of certain genes then they are referred to as” is (2) Merodiploid.

Explanation of options:

1. Amphidiploid – This refers to a type of polyploid organism that has two different sets of chromosomes derived from two different species, typical in eukaryotes, especially plants. It is not used for bacteria with two copies of certain genes.

2. Merodiploid – This term applies to bacterial cells that contain two copies of some genes, but not the complete genome. Such bacteria have partial diploidy for specific genes typically acquired by mechanisms like conjugation or gene duplication, making the bacteria partially diploid for those genes.

3. Euploid – This refers to cells or organisms having the normal, complete set(s) of chromosomes. In the bacterial context, this would mean having the typical haploid state of a single chromosome set, so this does not apply to bacteria with two copies of some genes.

4. Polyploid – It describes an organism or cell having more than two complete sets of chromosomes. While some bacteria can be polyploid, the question specifically mentions two copies of certain genes, not full sets of chromosomes, making this incorrect.

Introduction: In microbial genetics, the concept of bacteria possessing two copies of certain genes is crucial for understanding gene function and bacterial adaptation. When bacteria carry two copies of some genes but not the entire genome, they are referred to as merodiploid. This article explores what merodiploidy means, how it differs from other genetic terms like amphidiploid, euploid, and polyploid, and why it matters in bacterial genetics.

Detailed explanation:

Merodiploid bacteria contain two copies of specific genes, creating a partial diploid state. This condition usually arises during bacterial conjugation when a segment of DNA from a donor bacterium is integrated into the recipient bacterium’s chromosome. Unlike diploid eukaryotic cells, which contain two full sets of chromosomes, merodiploid bacteria only have duplicated segments of their genome, allowing researchers to study gene function and complementation.

In contrast, amphidiploid is a term used in eukaryotes to describe organisms with two full sets of chromosomes from different species. Euploid describes cells with the normal complete chromosome set, common in bacteria as they are typically haploid with a single chromosome set. Polyploidy occurs when cells have more than two full chromosome sets; some bacteria may be polyploid, but the presence of two copies of certain genes does not necessarily mean polyploidy.

Understanding these distinctions helps in genetic studies, including microbial gene mapping, horizontal gene transfer, and bacterial evolution.

This article clarifies these terms to help microbiology students, educators, and researchers better understand bacterial gene copy variations and their implications.

References for topic understanding include bacterial genetics and gene duplication studies.​

If you want, I can also prepare a more detailed article or provide explanations of bacterial gene duplication mechanisms.