Video Transcript
Which of the following best defines
multiple alleles for a given trait? (A) Multiple alleles refers to
three or more alleles occupying the same locus. (B) Multiple alleles refers to both
alleles for a trait being simultaneously expressed in the phenotype. Or (C) multiple alleles refers to
an organism that is heterozygous for an allele expressing a distinct intermediate
phenotype.
This question asks us how to define
the term multiple alleles. Multiple alleles refers to a
non-Mendelian mode of inheritance. We call it non-Mendelian because it
does not adhere to the typical inheritance of dominant and recessive alleles that
Gregor Mendel observed in his pea plants. For genes that had two alleles,
Gregor Mendel observed that one allele exhibited dominance over the other. This was made evident in his
crossing of purple- and white-flowering pea plants, with purple being the dominant
allele.
However, if three or more alleles
are present for a particular trait, inheritance becomes more complicated. When three or more alleles occupy
the same locus for a trait, the trait is considered to have multiple alleles. An example of this are blood types
in humans. Because blood types include the A,
B, and O alleles, it is a trait determined by multiple alleles. While these three alleles exist, an
individual will only ever possess two of these alleles, one from their biological
mother and one from their biological father. For instance, an individual could
be AA, BB, AB, AO, BO, or OO but never ABO.
Now that we know the definition of
multiple alleles, we can answer our question correctly. The correct answer to “Which of the
following best defines multiple alleles for a given trait?” is answer choice
(A). Multiple alleles refer to three or
more alleles occupying the same locus.
