MBB 141 Exercises 090207

1. Genes met and thi are linked in Neurospora crassa; we want to locate arg with respect to met and thi. From the cross arg + + x + thi met (+ means wild-type, while italicized means mutant), the following random ascospores were obtained

arg thi met, 26
arg thi +, 17
arg + met, 3
+ thi met, 56
arg + +, 51
+ thi +, 4
+ + met, 14
+ + +, 29

Map the three genes.

2. Genes a and b are linked, with 10 percent recombination. What would be the phenotypes, and the probability of each, among progeny of the following cross?

(a b+/a+ b) x (a b/a b)

(a+ means mutant while a means wild-type; the organisms are diploid, indicated by the slash)

3. Use the following two-point recombination data to map the genes concerned, and show the order and the length of the shortest intervals:

Gene loci, % recombination

a,b, 50
a,c, 15
a,d, 38
a,e, 8
b,c, 50
b,d, 13
b,e, 50
c,d, 50
c,e, 7
d,e, 45

4. One parent heterozygous for three linked alleles (C,c,Sh,sh,Bz,bz) is test-crossed with a parent homozygous for the recessive version of all three alleles (c,c,sh,sh,bz,bz)

Breeding data are shown in this table. Position the three genes on a genetic map using this information.

Group	Genotype	Crossovers	Number	Totals
1	CShBz	None; the parentals	479	952
2	cshbz		473
3	C|shbz	Single; between C and others	15	28
4	c|ShBz		13
5	CSh|bz	Single, between Bz and others	9	18
6	csh|Bz		9
7	C|sh|Bz	Double recombinants	1	2
8	c|Sh|bz		1
		Totals	1000