In rabbits, chocolate-colored fur (w +) is dominant to white fur, straight fur (
ID: 223339 • Letter: I
Question
In rabbits, chocolate-colored fur (w +) is dominant to white fur, straight fur (c +) is dominant to curly fur (c), and long ear (s +) is dominant to short ear (s). The cross of a trihybrid rabbit with straight, chocolate-colored fur and long ears to a rabbit that has white, curly fur and short ears produces the results in the table. a. Determine the order of the genes on the chromosome. b. Identify the alleles that are present on each of the homologous chromosomes in the trihybrid rabbits. c. Calculate the recombination frequency between c and w pair of genes. d. Calculate the recombination frequency between w and s pair of genes. e. Determine the interference value for this cross.Explanation / Answer
Answer:
a).
The order of genes is -----
s------25.21 m.u.---------- w---13. 36m.u.--c
b). s w+ c+ / s+ w c
c). RF between c & w = 13.36%
d). RF between w & s = 25.21%
e). 0.45
Explanation:
Shorthand
Number of progeny
Class
w s c+
13
double cross over
w+ s+ c+
165
double cross over
w+ s+ c
13
single cross over
w s+ c+
82
single cross over
w+ s c+
436
single cross over
w+ s c
79
single cross over
w s c
162
Parental cross over
w s+ c
450
Parental cross over
Total
1400
Imagine the parental genotype of gametes are w+ s c+ & w s+ c
1. If single cross over (SCO) occurs between w+ & s and w & s+
Normal order= w+---------s & w-----s+
After cross over= w+------s+ & w-----s
w+------s+ recombinants are 165+ 13 = 178
w-----s recombinants are 162 + 13 = 175
Total recombinants = 353
RF = (353/1400.)*100 =25.21%
2. If single cross over (SCO) occurs between s & c+ and s+ c
Normal order= s---------c+ & s+----c
After cross over= s-----c & s+------c+
s-----c recombinants are 79+162= 241
s+------c+ recombinants are 165+82 = 247
Total recombinants = 488
RF = (488/1400)*100 = 34.86%
3. If single cross over (SCO) occurs between w+ & c+ and w & c
Normal order= w+---------c+ & w------c
After cross over= w+-----c & w------c+
w+ -----c recombinants are 13+79= 92
w------c+ recombinants are 13+82= 95
Total recombinants = 187
RF = (187/1400)*100 =13.36%
% RF = Map unit distance
Distance between the w & s = 25.21 mu
Distance between the s & c = 34.86 mu
Distance between the w & c = 13.36 mu
The order of genes is -----
s------25.21 m.u.---------- w---13. 36m.u.--c
RF between s & w = 25.21% = 0.2521
RF between w & c = 13.36% = 0.1336
Expected double cross overs = 0.2521 * 0.1336 = 0.0337
The correct parental genotype of gametes are s w+ c+ & s+ w c
Observed double cross overs are s w c+ & s+ w+ c = 13 + 13
= 26/1400 = 0.0186
Observed double cross progeny are more than the expected double cross over progeny.
Coefficent of coincidence (CC) = Obeserved dco / Expected dco
CC = 0.014/0.032 = 0.55
Interference = 1-CC = 1-0.55 = 0.45
Shorthand
Number of progeny
Class
w s c+
13
double cross over
w+ s+ c+
165
double cross over
w+ s+ c
13
single cross over
w s+ c+
82
single cross over
w+ s c+
436
single cross over
w+ s c
79
single cross over
w s c
162
Parental cross over
w s+ c
450
Parental cross over
Total
1400
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