8. A genetics student crossed flies with normal long wings...

8. A genetics student crossed flies with normal long wings with flies expressing the dumpy mutation (truncated wings), which she believed was a recessive trait. In the F1 generation, all flies had long wings. The following results were obtained in the F2 generation when the F1 flies were mated: 792 long-winged flies 208 dumpy-winged flies. The student tested the hypothesis that the dumpy wing is inherited as a recessive trait using $chi^2$ analysis of the F2 data. A. What ratio ($H_0$) was hypothesized? (1 point)

Transcript

00:01 We're doing a bench next year where we're told that the f1 generation is made up of heterozygous individuals.

00:07 So this type, this genotype.

00:10 Now, if we cross two people who are heterozygous, then we can do a little punnet square to see what we would expect in their offspring.

00:20 When we do this, we see that we would expect 25 % to be homozygous dominant, 50 to be heterozygous and 25 % to be homozygous.

00:30 Recessive.

00:31 Those are the genotypes.

00:32 However, if we wanted to look at phenotypes, we would expect that three out of four options, or 75 % of the offspring, to have the dominant phenotype, and then the other 25 % to be homozygous recessive and have that recessive phenotype.

00:48 So when we look at the next generation, we are told that there's 792 who have this dominant trait, and and 208 who have the recessive trait.

01:10 Okay, so those are the information that we need to identify the observed amount of offspring for each phenotype in this f2 generation.

01:23 So what we have to do now is calculate what we would expect the expected number to be, so that way we can do the chai square test to see if we were correct.

01:34 So if we would expect that 75 % would have this dominant trait, then what we're going to do is we're going to take 75%, which on your calculator looks like 0 .75, multiply it by the total number of offspring, which is 1 ,000.

01:50 And you do that, you should come up with a number, in this case 750.

01:55 So we would expect that out of all the offspring, approximately 750 would have the dominant phenotype.

02:01 Then we can do the same thing for the recessive.

02:03 We take that percentage 25, turning to decimal, 0 .25, multiply it by the total number of offspring, 1 ,000.

02:10 So then we would expect that approximately 250 offspring would have that recessive phenotype...

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