Question

31. ANALYSIS Priscilla Lane and Margaret Green studied the linkage relations of three genes affecting coat color in mice: mahogany (mg), agouti (a), and ragged (Rg). They carried out a series of three-point crosses, mating mice that were heterozygous at all three loci with mice that were homozygous for the recessive alleles at these loci (P W. Lane and M. C. Green. 1960. Journal of Heredity 51:228-230). The following table lists the results of the testcrosses. Number Phenotype Rg 1 mg 15 Rg mg 16 Rg 36 mg 76 mg Rg 69 Total 213 Note: represents a wild-type allele. a. Determine the order of the loci that encode mahogany, agouti, and ragged on the chromosome, the map distances between them, and the interference and coefficient of coincidence for these genes. b. Draw a picture of the two chromosomes in the triply heterozygous mice used in the testcrosses, indicating which of the alleles are present on each chromosome. c. What information does the coefficient of coincidence give us? d. Explain why a calculation might return a negative interference and explain what this means e. Why does interference occur in double crossovers? + +

Answer 1

Phauotope Number Paremtal Parental 16 + + + a s mg a Ra Ma 36 s00 at Tegiou 1 9 Re mg 15 J a t + 1SCO at egion Parental ++ mg Ra Rg a + mg 1 a Ra + Recombinant 69 DCO + 76 Parenta) 213 mg SCo (at region 1)- 79.346mu 9+15)+(61-116) xi00'/,79.347. 213 at SCo 69.0omy HD(69+76)) 00 = 69.017. m 213 (9+15)+ (1+1)+2(69+76) l00 ' DCO T&tal Mab distance 213 cY 146.296my. = 146.24' Gui Not fin seale Mab T 69.011 71346m - 146.29nm 0 6901 X1000) Coe ficient Co-fncidence C0.C 0.264 Iemterferenca --coo) 0.264)O 736 in kerference In mefosis Im genaral 4hst accu. Yormation chmmosums rosoves duing the povide desree of inlerference Negative inkrference describe te of dwng Thus it metons OCcu ituahion m which tuo genetc regnon have mare Consadesing dco tham would be each regron expecte CYusove Tf double CTOSS aver doeo mot ocur during metosn's. amd mo Chmmosomal excheng between ster crom ah'ds occu the re presemt than there mderferente ,but f mlerfere n ce, ike in above Caoe oM be mo C06) CoTi be