Determine the most likely mode of inheritance for each set...

Determine the most likely mode of inheritance for each set of crossing data. Each system is independent of the others. Initial parents are pure-breeding in each case. Blue frogs x yellow frogs -> all green -> 95 green, 33 yellow, 31 blue, 12 white Green frogs x white frogs -> all green F1s; F1-green x white -> 35 green, 35 white, 15 blue, 15 yellow Green frogs x white frogs -> all green -> 95 green, 40 white, 31 yellow Purple frogs x white frogs -> all green -> 62 green, 48 blue, 47 yellow, 12 purple, 11 white

Transcript

00:01 Most of the time when we have a diehybrid cross where we have two totally heterozygous individuals that we cross, like here it's dominant a, recessive a, dominant b, recessive b.

00:10 For both of these individuals, you cross them, you end up with this punnet square.

00:17 Now, when we look at classic mendelian genetics, where you have dominant and recessive genes, you would end up with this phenotypic ratio.

00:28 So you have nine who have both dominant traits, three who have just the a dominant trait, three who have just the b dominant trait, and one out of every 16 who have no dominant traits.

00:43 That is for classic mendelian dominance and recessiveness.

00:48 However, there are a lot of forms of epistasis that can skew this 9 to 3 to 1 ratio.

00:56 I'm going to talk about some of the most common.

00:58 So one of the most common is recessive epistasis.

01:07 For recessive epistasis, we are going to have a nine to three to four ratio.

01:14 And it's just what you would expect.

01:16 We have the nine, which is both dominant traits.

01:20 We have three, which is having the first dominant trait.

01:23 We're having one of the dominant traits.

01:26 But then we find that if there are any chances of having both recessive genes for the first trait.

01:39 If you have any at all, regardless of whether you have dominant or recessive alleles for the secondary trait, you will have one phenotype.

01:49 Right.

01:49 So whether you have two recessive a's and dominant b's or two recessive a's and no dominant b's, you're going to have the same phenotype.

01:59 So in this situation, this double recessive a is your epistasis.

02:06 That's the specific combination of alleles that will override the phenotype and will determine what the offspring will look like.

02:18 Now, there's a similar situation of dominant epistasis.

02:29 In dominant epistasis, we have a ratio of 12 to 3 to 1.

02:36 So 12 is if we have any dominant a.

02:43 So if you have one or two dominant a's, it does not matter what the bs are.

02:49 You will have this certain phenotype because in this case, dominant a is the override...

Question

Please give Ace some feedback