Homework SourseThe F2 progeny of a three point cross of the mosquito Culex
The F2 progeny of a three point cross of the mosquito Culex pipiens, one of 38 species of mosquitoes resident in New Brunswick, are tabled below. The X-linked genes st, ss, and e code for scarlet eyes, spineless bristles, and ebony body, respectively. Wild type alleles st+, ss+ and e+, code for dark eyes, smooth bristles and gray body, respectively. 4a. Complete the table below by filling in the phenotypes of each class: F2 Class Genotype Number Observed Phenotype 1 st ss+ e+ 570 2 st+ ss e 602 3 st ss e+ 38 4 st+ ss+ e 47 5 st ss e 88 6 st+ ss+ e+ 101 7 st ss+ e 4 8 st+ ss e+ 5 1455
F2
Class
Genotype
Number Observed
Phenotype
1
st ss+ e+
570
2
st+ ss e
602
3
st ss e+
38
4
st+ ss+ e
47
5
st ss e
88
6
st+ ss+ e+
101
7
st ss+ e
4
8
st+ ss e+
5
1455
4b. Determine the gene order:
4c. Determine the linkage distances. Use proper units. (SHOW YOUR WORK)
4d. Draw the gene map.
4e. Calculate the Coefficient of Coincidence: (SHOW YOUR WORK)
4f. Calculate interference: (SHOW YOUR WORK)
| F2 Class | Genotype | Number Observed | Phenotype |
| 1 | st ss+ e+ | 570 | |
| 2 | st+ ss e | 602 | |
| 3 | st ss e+ | 38 | |
| 4 | st+ ss+ e | 47 | |
| 5 | st ss e | 88 | |
| 6 | st+ ss+ e+ | 101 | |
| 7 | st ss+ e | 4 | |
| 8 | st+ ss e+ | 5 | |
| 1455 |
Solution
F2
Class
Genotype
Number Observed
Phenotype
1
st ss+ e+
570
Scarlet, smooth, gray
2
st+ ss e
602
Dark, spineless, ebony
3
st ss e+
38
Scarlet, spineless, gray
4
st+ ss+ e
47
Dark, smooth, ebony
5
st ss e
88
Scarlet, spineless, ebony
6
st+ ss+ e+
101
Dark, smooth, gray
7
st ss+ e
4
Scarlet, smooth, ebony
8
st+ ss e+
5
Dark, spineless, gray
1455
Parental combinations are more so, the parental combinations are st ss+ e+ & st+ ss e
1. If single cross over (SCO) occurs between st & ss+
Normal order= st ---------ss+ & st+ ----- ss
After cross over= st ----- ss & st+ ------ ss+
st ----- ss recombinants are 38+88=126
st+ ------ ss+ recombinants are 101+47=148
Total recombinants = 274
RF = (274/1455)*100 =18.83%
2. If single cross over (SCO) occurs between ss+ & e+
Normal order= ss+ --------- e+ & ss --------- e
After cross over= ss+ --------- e & ss ------ e+
ss+ --------- e recombinants are 4+47= 51
ss ------ e+ recombinants are 5+38=43
Total recombinants = 94
RF = (94/1455)*100 = 6.46%
3. If single cross over (SCO) occurs between st & e+
Normal order= st --------- e+ & st+------e
After cross over= st --------- e & st+ --------- e+
st --------- e recombinants are 88+4=92
st+ --------- e+ recombinants are 101+5= 106
Total recombinants = 198
RF = (198/1455)*100 = 13.61%
% RF = Map unit distance
The order of gene is -----
st ---------13.61 m.u.----------e----6.46 m.u.----ss
Expected double cross over frequency (EDCO) = (RF of s&e) (RF of e & ss)
= 0.1361 * 0.0646= 0.009
Observed double cross over frequency (ODCO)= (4+5)/1455 =0.006
Coefficient of Coincidence (coc)= ODCO/ EDCO = 0.006/0.009=0.67
Interference= 1-coc= 1-0.67=0.33
| F2 Class | Genotype | Number Observed | Phenotype |
| 1 | st ss+ e+ | 570 | Scarlet, smooth, gray |
| 2 | st+ ss e | 602 | Dark, spineless, ebony |
| 3 | st ss e+ | 38 | Scarlet, spineless, gray |
| 4 | st+ ss+ e | 47 | Dark, smooth, ebony |
| 5 | st ss e | 88 | Scarlet, spineless, ebony |
| 6 | st+ ss+ e+ | 101 | Dark, smooth, gray |
| 7 | st ss+ e | 4 | Scarlet, smooth, ebony |
| 8 | st+ ss e+ | 5 | Dark, spineless, gray |
| 1455 |
