Video Transcript
Using the knowledge gained from
Mendel’s experiments with pea plants, the law of dominance was formed. Which of the following best
describes this law? (A) The inheritance of one trait
from parents to offspring does not affect the inheritance of another. (B) When traits are inherited from
parents to offspring, one trait can completely mask the appearance of another. (C) Traits are controlled by
factors that are passed from parent to offspring. (D) An organism can have only one
defining characteristic at a time.
Mendel used pea plants to study
inheritance. He bred various pea plants together
through cross-pollination to determine which traits were passed down to the
offspring and which weren’t. One theory that he proposed is the
law of dominance. This law explains that if a parent
with two dominant alleles reproduces with another parent with two recessive alleles,
then all the offspring will display the dominant trait.
Peas can be green or yellow in
color. And these traits are controlled by
two different versions of a gene called alleles. The uppercase A is the dominant
allele, and the lowercase a is the recessive allele. Notice that all the offspring in
this example are yellow, which is the dominant trait indicated by uppercase A. Even though the offspring contain
both the dominant and recessive allele, only the dominant trait is expressed. You need two copies of the
recessive allele for that trait to be expressed, as shown here with the green color
with the two recessive alleles.
We can summarize all this here. Dominant traits are always
expressed if they’re present, while recessive traits are only expressed if the
dominant trait is absent.
Now let’s take a look at the answer
choices to determine the best one.
Answer choice (A) is incorrect. This option describes another one
of Mendel’s laws, but not the law of dominance.
Answer choice (B) seems to be
correct. As we had shown on the right,
having only a single copy of the dominant allele can mask the appearance of the
recessive trait. But before making our final
decision, let’s look at the remaining options.
Answer choice (C) is incorrect. While it is true that the traits of
an organism depend upon the genetic factors that are passed down from the parents,
this is not what the law of dominance states.
Answer choice (D) is incorrect. Every organism has multiple traits
that make them unique from another.
Therefore, the option that best
describes the law of dominance is given by answer choice (B). When traits are inherited from
parents to offspring, one trait can completely mask the appearance of another.
