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| Name | Three point mapping II Gene Order II Gene Distance II Genetics Problem Linkage |
| Video Uploader | Video From BioMagica |
| Upload Date | This Video Uploaded At 30-08-2019 18:19:47 |
| Video Discription | Let us learn how to solve three point linkage cross using 4 simple steps With 3 genes There are 3 possible cross over type or recombination that can take place Lets take the example of two parent type ABC and abc, A single crossing over can happen between genes A and B, or between genes B and C, or double cross over can happen between genes AB and BC. The recombinants by a single cross over between A and B will be Abc and aBC Similarly, a single crossover between genes B and C will give Abc and abC recombinants A double crossover between genes AB and BC will give Similarly in the second condition, the recombinants will be In every question we have 8 types of Gametes, two Parental, two SCO between genes 1-2, 2 sCO between genes 2-3 and 2 DCO. It is very easy to identify the parental and DCO gametes in most of the questions The gametes showing the highest number of progenies are parental types, and the gametes showing the lowest number of progenies are the DCO types. Let's look at this question where we need to find the distance between the genes and we provided with the genotype and number of observed progeny. To solve this we must know the type of gamete Our first step is to find the parental and DCO types. As we know the highest number of progenies are parental types and the lowest number of progenies come from DCO The question mentions the genes as ABC, but the actual gene order can be different To find the gene order, we will compare the parental and the DCO type On comparison, we notice that C gene does not match in the parental and DCO type, thus C gene is present in the center of gene A and B The third step is to determine SCO between genes. Considering this gene order ACB, we will do a single cross of the two parental type between genes A and C The recombinants obtained by this cross will be Acb and aCB Now we need to compare this recombinant with the table in the question. If we rearrange this, we have Capital A and small bc and small a and capital BC recombinants which are our single crossovers between genes A-C So naturally, the remaining two genotypes are SCO between genes C and B. You can do a crossover yourself and check. The 4th step is to determine the distance between the genes. To determine the distance between genes A and C we need to add the sum of SCO between AC and DCO progenies, divide by total progenies * 100 Which is 17.9 cM apart Similarly, the distance between genes C and B will be the sum of the SCO between genes CB and DCO progenies divided by total progenies *100 which is 7cM The distance from A-C is 17 cM, and the distance between C-B is 7 cM For some problems like this one, we must use an alternative approach. Since the values are not letting us decide the parental and DCO types we cannot follow our 4 steps here When crossing over occurred between two genes, the two gene forms will not be together in the recombinants Like crossing over occurred between capital A and capital B, but in the recombinants, Capital A and Capital B will not be together. Similarly, when crossing over occurred between capital B and Capital C, the recombinants will not have both capital forms together Capital A and small a are two forms of the gene Similarly, in this problem + and or no plus are two forms. So another way to identify Recombinants is by finding combinations where the two forms are not together. Like in p q r and P+Q+R+…both are in same form so we won't consider these Here p and r are in different forms Similarly, we select all combinations where they p and r are in different forms three point test cross gene mapping three point cross genetics three point cross gene mapping problems gene mapping |
| Category | Education |
| Tags | CSIR | NET | three point test cross gene mapping | three point cross genetics | gene mapping | mapping | linkage mapping | three point | three point cross | gene mapping problems | mapping problems | genetics problems | gene distance | three point gene | gene order | recombination frequency problems | recombinants | parental genotypes |
