AP Biology 2.1 Essential Life Process Information

AP Biology 2.1 Essential Life Process Information. What is the simplest interpretation of the results?

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00:22

What is the simplest interpretation for these results?

00:24

Here are the potential answers…

00:27

Okay, here we go.

00:30

To keep it simple, let’s first assume that feather color is a single trait under the [Bird spreading its wings]

00:34

control of a somatic gene on a single chromosome.

00:39

This already eliminates answers C and D, since dihybrid crosses involve two different traits,

00:44

and sex-linkage involves the two sex chromosomes, rather than the other somatic chromosomes.

00:50

This leaves us with options A and B. First, let’s think about what phenotypes

00:55

we’re seeing.

00:56

The phenotype is what’s physically displayed, while the genotype is what is encoded genetically. [Girl and guy looking puzzled]

01:01

So taking a look at this question, we see three phenotypes: black, white, and gray. [Three birds on a branch]

01:05

Now we need to think about what their genotypes are…

01:08

We're thinking bell-bottom, but…don't hold us to that. [Three phenotypes wearing jeans]

01:11

Since feather color is a trait controlled by a single allele, when a new baby bird is

01:15

born, there are three possibilities for its genotype: (1) it inherits two dominant alleles

01:21

– this is called “homozygous dominant” (2) it inherits a dominant and a recessive

01:26

allele, or “heterozygous”, or (3) it inherits two recessive alleles – called “homozygous

01:32

recessive”.

01:33

Huh.

01:34

Really thought "bell-bottoms" would be a choice for genotype…

01:36

Anyway.

01:37

The question is, which color is dominant?

01:39

Let’s assume black feathers are dominant here. [Black birds and white birds in a field]

01:41

If that’s the case, in a monohybrid cross, birds that are heterozygous should be black,

01:45

as black feathers would dominate over the gene for white feathers.

01:49

But we don’t see that – we see birds with gray feathers. [Black, Gray and White birds in a field]

01:52

This means that we are likely to have incomplete dominance – where heterozygotes show a mixture

01:57

of the dominant and recessive alleles for a trait.

01:59

Which means the answer for this question is (A).

02:02

Glad we came to the right answer.

02:03

Now we can dihybrid happy. [A gravestone for Science McScienceton]