00:01
If you have a monogenic phenotype, what this means is mono is one and genic refers to gene.
00:16
So this is a phenotype that is determined by one gene.
00:20
So the probability for a recessive phenotype in the f2 is one -fourth.
00:28
Now, if we have a polygenic phenotype, remember poly means many, and again, genic means gene, so this is a polygenic.
00:43
Phenotype that's caused by many genes, the f2 phenotype will again be one quarter for the recessive phenotype, but because we don't know how many genes are controlling that particular phenotype, it has to be to the end of power.
01:02
And so we can use this formula to solve part a in our problem.
01:08
Now, these two sort of rules apply if you have homozygous dominant parents.
01:16
Bread with each other.
01:19
It doesn't work if you have other combinations.
01:21
So the parental cross must be all homozygous dominant, cross with all homozygous recessive.
01:29
And so from the problem in part a, we know there are 256 individuals that were the outcome.
01:37
And so all we need to do is take this formula and use the information from a part in the question to determine the number of genes that are yielding a particular phenotype.
01:49
So here, one fourth to the end, we are going to convert that to 4 to the n power equals 256 from the problem.
02:02
We know that 4 to the fourth power is 256.
02:07
So n equals 4.
02:10
The number of genes in this problem that are controlling a given phenotype is that four.
02:23
Now for the part b part of the problem, let's make some notes.
02:32
We know that the minimum height of the plant is nine inches.
02:37
So an all recessive plant, so they would have two little a's, two little b's, two little c's.
02:46
I'm going to underline my sees because i get sloppy and then i won't be able to tell the difference and neither will you between a big c and a little c.
02:53
If you have a plant that's all recessive, that plant has a height of nine inches.
03:00
We also know that a plant that's all dominant, so big a, big a, big b, big b, two big c's and two big ds is 21 inches tall.
03:16
So then we can subtract to figure out the difference.
03:19
21 inches minus nine inches equals 12 inches.
03:25
We know that there there are four genes.
03:30
We know that there are four genes that are controlling this height phenotype.
03:40
And so we can determine the contribution to height by each gene.
03:52
And we have to assume that each gene contributes equally to the phenotype.
03:57
But we have no way of knowing that...