a. In Drosophila, crosses between F1 heterozygotes of the form A b / a B always yield the same r

step 1 Let's answer this question let's talk about inheritance. It says, three genes in fruit flies aff

A. In Drosophila, crosses between F1 heterozygotes of the...

Key Concepts

Genetic Linkage and Recombination

This concept involves understanding that genes on the same chromosome tend to be inherited together due to their physical proximity, with the frequency of crossing over between them being inversely related to their closeness. Recombination frequency, often expressed as a percentage (or centiMorgans), is used as an estimator of the map distance between genes and is a foundational principle in genetic mapping.

Cis and Trans Heterozygote Configurations

The configuration of alleles on homologous chromosomes – whether they are arranged in cis (AB/ab) or in trans (Ab/aB) – is crucial because it determines how recombination affects the segregation of alleles in progeny. In cis configurations, the parental alleles are on the same chromosome which makes the detection of recombination events dependent on the recombination frequency, while in trans configurations, certain phenotypic ratios may be maintained independent of the actual map distance between the genes.

Dominance in Inheritance Patterns

Dominance refers to the phenomenon where one allele masks the expression of another at the same locus. When both genes exhibit complete dominance, heterozygous individuals display the dominant phenotype regardless of whether they have a recombinant or parental genotype. This can simplify or complicate the interpretation of phenotypic ratios in genetic crosses, depending on the arrangement (cis vs trans) of the alleles.

Estimation of Map Distance from Progeny Ratios

Map distance estimation involves using the frequency of recombinant phenotypes in offspring to infer the distance between genes, typically expressed in centiMorgans. In cases where recombination events are directly observable from phenotype ratios, one can estimate the map distance by calculating the proportion of recombinant types. However, the ability to estimate map distances accurately can depend on the genetic configuration of the heterozygotes, as certain configurations (particularly when dominance masks the genotype) may obscure the actual recombination frequencies.

Transcript

00:01 Let's answer this question let's talk about inheritance.

00:03 It says, three genes in fruit flies affect a particular trait and one dominant allele of each gene is necessary to get a wild type phenotype.

00:13 So you have three genes, the a, the b, and the c gene, okay? if you want the wild type, then you need this genotype here.

00:22 This is going to be for the wild type, okay? it also says here that what phenotype in vitios would you predict among the progeny if you could? cross triply heterocygot flies.

00:35 It means you cross this, this with this and this.

00:44 Okay so this is what you're going to, what they're asking you to cross.

00:49 They're asking you for the phenotypic ratios that would you predict among the prergeny.

00:53 So in this case you don't need to make a panel, a three hybrid planet square, okay? you can make three monohydropadne square between this with this, this with this, this with this.

01:02 So you have heterozygos a, like this, then for the heterozygos b with the heterozygos v with the heterozygos v homozygous dominole, heterocygous, heterocygous and homozygose domineat, and finally for the heterozygoseygote c with the heterozygote c, you get homozygous nominant, heterozygous, heterozygos and homozygose decisive.

01:35 So, remember that whenever you have the dominant, the three genes you're going to have the wild type and all the remaining offspring or combinations are going to result in the no wild type phenotype okay so in this case what other chances to get dominant dominant a here you have three quarters because of a total of four possibilities one two and three are going to be dominant the same here three quarters in the same here three quarters so the probability to get the three dominant genotypes for the three genes are 27 out of 64 so as you have the 27 out of 64 i'm gonna have the wild type then the second genotype i'm gonna be it's gonna be the remaining between 64 and 27 it means 37 this is gonna be for the wild type and for the no wild type i don't know what is a phenotype because they are not telling us you're gonna have that remaining 37 okay because 37 plus 27 is 64 so um your phenotypic rate is gonna be 27 37 the next question says the next question says um you cross a particular wild type male in succession with three tester strains in the cross with one tester so here you are you have a wild type a organism okay like this a wild type fly but it is like this you don't know if it is homocygous dominant here or heterocygoyles or homocygous dominant here or homocygoyal dominant here or hydrocygios and the same here but this is that you're crossing you're making three crosses here okay the first tester is with this genotype here it's the homozygous dominant the homocygose offensive and homocygose recessive and it says that one quarter of the progeny are wild type so what is the only possible gamut produced from this parent the only possible gamete is this this is the only possible gamut okay and you don't have you don't know how many possible gamies this parent is going to have but it says that only one quarter of the progeny are wild type so out of four possibilities it means there are only four possibilities okay, one, two, three and four.

04:20 Out of four possibilities, only one is going to have the wild type, zero type.

04:24 So for sure, remember that you're going to find the gametes by mixing each of these a alil with each of this b alias and with each of these c alleles.

04:32 So in this case, if you're getting, or for sure here are going to get one gamete that is like this when you mix this dominant a with this dominant b and with this dominant c.

04:45 And in this, okay, out of four possibilities, only in this here you're gonna get homocygoyles dominant heterocygose and homozygose so here you have one wild type so this should be the only the only wild type that you get out of these four possibilities because it says that only one quarter of reprogyne are wild types so this should be the only one quarter or the only wild type so if this is the case then it is probably that two of them to be homozygotechized.

05:19 Dominant and only one is heterocygoth.

05:21 For example, we don't know which of them are homozygous dominant and which is the heterozygoyote.

05:25 But let's suppose that here you have the heterozygos and here you have homozygos dominant or homozygotts dominant.

05:30 So your gametes, your only two possible gametes or your gametes can be one and here two.

05:44 Okay, well let's suppose that this is like this.

05:47 Then you would have this and here you go to get.

05:53 Heterocygous, heterocygous and homocybo or hydrocygos, okay? this, yeah, yeah, two heterocygos.

06:01 So you would get two out of four.

06:04 So this is not a case actually, okay? so what is happening actually maybe is that you get two hetero cycles.

06:17 Like this.

06:18 Let's suppose that this is heterozygos.

06:21 If you have two heterozygos, then your gamete would be, well, this is one gamete then you would have this this this then this this this this and this then this this this this this this this this this would be your four gametes so let's try with this so let's complete you have homozygos dominant homozyglygos excessive heterocygios heterocygote heterocygous heaterozygos and hydrocygoyles heterozygos heterocygous homozyrocyl excessive and heterocygoyles and in this case as you can see here you have that our four possibilities this is wild type but also this is one type is wild type so you have two quarters wild type but this is not what you want you want one quarter to be wild type so this is not a case in there okay let's come back again and what may be happening is that that so now um what happens if we make if we make the a to be homozygos dominant here and he will make one of them to be heterocygo, for example, this one here.

07:39 Okay, so...

07:41 And also one of them also heterocygous, maybe this one here.

07:48 Heterocigos, okay? so what are i going to be yurgaamids? well, you have the a, b, and c, now you have the dominant a, dominant b, excessive c.

07:57 Then you have dominant a, decisive b, dominant c, dominant a, decisive b, decisive c...

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