BIOL239 Lecture 9: editedFontBIOL239set9 mapping (1)
17 Feb 2016
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Map distances chapter 4 pg 121 - 127 two-point crosses. Comparisons between different two-point crosses can help to establish relative gene positions. A. h. sturtevant : was able to determine an order for the genes he investigated on the. Mapping genes by comparisons of two-point crosses e. g. , genes y, w, v, m, r. Limitations of two-point crosses: in crosses involving genes lying close together it may be difficult to determine the correct order e. g. , if the distance a-b is 28. 2 m. u. , and the distance a-c is 29. 3 m. u. A single 2 point cross is not accurate for determining the distance between genes that are far away from each other. Have to do a series of 2 point crosses using other genes that lie between. A faster, more accurate method for mapping genes, through the simultaneous analysis of three marker genes. This method allows correction for double crossovers a. We have no way of knowing what the order is yet.
