Video Transcript
The gene that provides resistance
to the fungal disease potato blight is identified. How could this be used to produce a
population of blight-resistant potatoes? (A) Potato plants without the gene
for resistance could all be removed and destroyed. (B) The potato plants could be
genetically engineered to contain the gene for blight resistance. (C) Potato plants could be grown in
soils that contain this gene and absorb it into their roots. (D) There is no method of producing
a population of blight-resistant potatoes.
The question states that there
exists a gene which provides resistance against a specific disease. But how can we use the knowledge of
this specific gene to produce plants that are resistant against this specific
disease? Before we answer this question, we
first have to repeat some basic genetics.
You may remember that genes are
stored in DNA, which is packed up into chromosomes, which are passed down from the
parents to the offspring. Genes cannot be absorbed from
soil. And answer choice (C), potato
plants could be grown in soils that contain this gene and absorb it into their
roots, is therefore not a possible solution.
If we remove and destroy all potato
plants without the gene for resistance, we’d end up with none or very few remaining
plants. The potato production would
crash. If we do end up with a couple of
remaining undestroyed plants, we could use them to breed and might indeed end up
with a population of blight-resistant potato plants. However, this process would remove
a big part of the genetic variety of potato plants as the new blight-resistant
population would be very inbred, leading to a new set of problems.
If, for example, the few remaining
plants had next to the resistant gene another mutation, causing for example a sour
taste of the potato, the whole new population of potato plants would produce
sour-tasting potatoes. And there are no other plants left
with which we could cross them to get rid of this unfortunate mutation.
As the production of
blight-resistant potatoes in this way would lead to a crash in potato production and
requires that some of the plants need to contain the gene for resistance, answer
choice (A) does not give us a valid option to produce a blight-resistant potato
population.
There are, however, other ways with
which a blight-resistant potato plant population with a certain amount of genetic
variation can be produced. The first one is the process of
selective breeding. We can select individual plants
which do have a version of the gene that provides resistance to the fungal disease
potato blight. These selected individuals are then
artificially bred together. Their offspring is then screened to
see if their parents passed down the gene causing potato blight resistance. Those that do are bred together
again, and the process is repeated over several generations. This can lead to a large proportion
of plants resistant to a disease and even to a blight-resistant population of potato
plants.
The second possible way to produce
a population of blight-resistant potatoes is called genetic engineering. When we genetically engineer a
plant, we physically edit the DNA of the plant. With this method, the gene that
codes for potato blight resistance can be incorporated into the DNA of the
plant. As plants grow quickly and are easy
to clone, a large proportion of the population that is resistant to this specific
disease can easily be created. With this knowledge, we can now
identify the correct answer. The potato plants could be
genetically engineered to contain the gene for blight resistance.
