Correct option is C
Let’s break down the statements and match them with the correct terms:
Statement A: A transgenic plant with two functional copies of a transgene can segregate in a ______ ratio for the transgenic phenotype on self-pollination if the two genes are linked.
The segregation ratio for linked genes on self-pollination would follow the 3:1 Mendelian ratio typical for a dihybrid cross involving two heterozygous loci, where the genes are linked. This indicates that the correct ratio is 3:1.
Statement B: The ______ system can be used for removal of marker genes from transgenic plants.
The Cre/loxP system is a well-known recombination system used for excising unwanted marker genes from transgenic plants, so the correct term here is Cre/loxP.
Statement C: The endogenous plant gene ______ can be used to engineer resistance to imidazolinone herbicides.
The ALS (Acetolactate synthase) gene is often used to confer herbicide resistance in plants, particularly to imidazolinone herbicides, which target ALS. Therefore, the correct term is ALS.
Statement D: Variations in transgene expression levels between five independent transgenic lines generated using the same T-DNA construct can be due to ______.
Variations in expression levels of transgenes can arise due to the position effect, which refers to the influence of the genomic location of the transgene insertion on its expression. The correct term is position effect.
Thus, the correct sequence of terms to fill in the blanks is:
A-3:1; B-Cre/loxP; C-ALS; D-position effect
Information Booster
Cre/loxP system: The Cre/loxP system is a site-specific recombination system used to remove unwanted genes (e.g., marker genes) from transgenic plants. Cre is an enzyme that recognizes the loxP sequence and facilitates recombination between loxP sites, excising the gene between them.
ALS (Acetolactate Synthase): The ALS gene is involved in the biosynthesis of branched-chain amino acids. By introducing modified ALS genes into plants, researchers can confer resistance to herbicides like imidazolinone that inhibit this enzyme. It’s one of the most widely used methods for herbicide resistance in transgenic crops.
Position effect: Position effect refers to the impact of the genomic location of a transgene on its expression. Transgenes inserted in different parts of the genome can have different expression levels, even if the same construct is used, due to factors such as surrounding heterochromatin or nearby regulatory elements.
