Question

When a transgenic plant is crossed with a non-transgenic, what would be the zygosity status of the F1 plant?

• A. Homozygous
• B. Heterozygous
• C. Hemizygous
• D. Nullizygous

Hint:

Zygosity terminology in Transgenics:
One copy = Hemizygous.
Two copies = Homozygous.
No copy = Nullizygous (often used as a control in experiments).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks about the genetic state (zygosity) of a first-generation (\( F_1 \)) plant resulting from a cross between a transgenic parent (containing an inserted gene) and a wild-type (non-transgenic) parent.
Detailed Explanation:

• Definition of Hemizygous:
In a typical transgenic plant, the foreign DNA (transgene) is integrated at a specific locus on one of the homologous chromosomes.
Because there is no corresponding allele or locus on the other homologous chromosome in the wild-type genome, the plant carries only one copy of the gene at that locus. This state is called Hemizygous.

• Analysis of the Cross:
Let the transgene be \( T \) and the corresponding empty locus in the non-transgenic plant be \( - \).
Transgenic Parent (usually hemizygous \( T- \) or stable homozygous \( TT \)) \( \times \) Non-transgenic (\( -- \)).
If we assume the primary transgenic line (which is hemizygous) is crossed:
\( T- \times -- \rightarrow 50\% \text{ are } T- \) (Hemizygous) and \( 50\% \text{ are } -- \) (Nullizygous).
In biotechnology, the term "Heterozygous" is often avoided for transgenes because "Hetero" implies two different alleles (\( Aa \)). Since there is no "allele" at all on the other chromosome, "Hemizygous" is the technically accurate term.

• Other Terms:
Homozygous: Carrying two identical copies (\( TT \)). This is achieved after selfing the \( F_1 \) for several generations.
Nullizygous: Lacking the transgene entirely (\( -- \)).

Step 3: Final Answer:
The resulting transgenic offspring in the \( F_1 \) generation are Hemizygous.