The Question is from neet-botany biotechnology transgenic-animals, and it was created by the author Mr. NARESH KUMAR K

Question

A transgenic mouse expressing a human growth hormone gene exhibits gigantism.  Researchers discover a second transgenic mouse line with the same human growth hormone gene construct, yet these mice show normal growth.  Which of the following is the MOST LIKELY explanation for this discrepancy?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Transgenic expression and gene regulation
 **Related Topics**: Epigenetics, gene silencing, position effect variegation
 **Prerequisites**: Understanding of gene expression, transgene integration, and epigenetic mechanisms.
## SOLUTION PATHWAY
**Given Information**:
  * Two transgenic mouse lines with the same human growth hormone gene construct.
  * One line shows gigantism (overexpression of growth hormone).
  * The other line shows normal growth.
  * The difference lies in the effect of the transgene.
**Method & Steps**:
 1. Analyze the options to identify the most likely cause of the discrepancy.
  Reasoning: We need to explain why one mouse line expresses the human growth hormone effectively while the other doesn't, despite having the same gene construct.
 2. Evaluate each option:
  Option A: A mutation in the mouse growth hormone receptor would affect both mouse lines, not just one. This is less likely.
  Option B: If the human growth hormone gene isn't transcribed, there would be no protein produced. However, the gene construct is identical, making this unlikely without an additional factor affecting transcription. 
  Option C: Position effect variegation (PEV) is a phenomenon where the expression of a gene depends on its chromosomal location.  If the transgene inserts into a region of heterochromatin (tightly packed DNA) in the second mouse line, it may be silenced or expressed at a very low level, leading to normal growth. This is a plausible explanation for the difference between the two lines.
  Option D: An endogenous inhibitor would likely affect both mouse lines, unless the inhibitor's expression itself is somehow influenced by the transgene's insertion site (though this is less direct than PEV).
 3. Conclusion:
  Result: Position effect variegation (Option C) is the most likely explanation. The insertion site of the transgene can dramatically influence its expression level due to epigenetic effects.
  Verification: PEV is a well-documented phenomenon that can lead to variable expression of transgenes depending on their insertion site.  This explains why one mouse line shows gigantism while the other has normal growth, despite having the same gene construct.
 ## OPTION ANALYSIS
A :x:  A mutation in the mouse growth hormone receptor would affect both lines.
B :x:  Lack of transcription would likely affect both lines unless a specific regulatory element was affected by the insertion site.
C ✓: Position effect variegation explains the variable expression of the transgene due to its insertion site.
D :x: An endogenous inhibitor is less likely to only affect one line unless its expression is influenced by the transgene's insertion site, which is less direct than PEV.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming that the difference is due to a mutation in the gene itself rather than its regulation.
   How to avoid: Consider epigenetic mechanisms and other factors affecting gene expression beyond simple mutations.
  2.Overlooking the role of chromatin structure and position effects in gene expression.
   How to avoid: Remember that gene expression is not solely determined by the gene sequence but also by its chromosomal context.
 **Quick Tips**:
  1.When comparing transgenic lines with the same construct, consider epigenetic factors like PEV as a primary cause of differences in gene expression.
  2.Remember that the chromosomal location of a transgene can significantly affect its expression level.

Mr. NARESH KUMAR K · Answer

The second mouse line has a mutation in the mouse growth hormone receptor gene.

Mr. NARESH KUMAR K · Answer

The human growth hormone gene is not being transcribed in the second mouse line.

Mr. NARESH KUMAR K · Answer

The correct Option is "Position effect variegation due to the transgene's insertion site in the second mouse line."

Mr. NARESH KUMAR K · Answer

The second mouse line expresses an endogenous inhibitor of human growth hormone.

NEET Botany Biotechnology and Its Applications Transgenic Animals MCQs

Select Topic

Question Tags

NEET Subjects

Our Bots

Company