AP Biology 2.1 Essential Life Process Information. What is the simplest interpretation of the results?
|AP Biology||Essential Life Process Information|
|Test Prep||AP Biology|
What is the simplest interpretation for these results?
Here are the potential answers…
Okay, here we go.
To keep it simple, let’s first assume that feather color is a single trait under the [Bird spreading its wings]
control of a somatic gene on a single chromosome.
This already eliminates answers C and D, since dihybrid crosses involve two different traits,
and sex-linkage involves the two sex chromosomes, rather than the other somatic chromosomes.
This leaves us with options A and B. First, let’s think about what phenotypes
The phenotype is what’s physically displayed, while the genotype is what is encoded genetically. [Girl and guy looking puzzled]
So taking a look at this question, we see three phenotypes: black, white, and gray. [Three birds on a branch]
Now we need to think about what their genotypes are…
We're thinking bell-bottom, but…don't hold us to that. [Three phenotypes wearing jeans]
Since feather color is a trait controlled by a single allele, when a new baby bird is
born, there are three possibilities for its genotype: (1) it inherits two dominant alleles
– this is called “homozygous dominant” (2) it inherits a dominant and a recessive
allele, or “heterozygous”, or (3) it inherits two recessive alleles – called “homozygous
Really thought "bell-bottoms" would be a choice for genotype…
The question is, which color is dominant?
Let’s assume black feathers are dominant here. [Black birds and white birds in a field]
If that’s the case, in a monohybrid cross, birds that are heterozygous should be black,
as black feathers would dominate over the gene for white feathers.
But we don’t see that – we see birds with gray feathers. [Black, Gray and White birds in a field]
This means that we are likely to have incomplete dominance – where heterozygotes show a mixture
of the dominant and recessive alleles for a trait.
Which means the answer for this question is (A).
Glad we came to the right answer.
Now we can dihybrid happy. [A gravestone for Science McScienceton]