In a plant leaf color, leaf shape, and plant height are controlled by three link
ID: 191839 • Letter: I
Question
In a plant leaf color, leaf shape, and plant height are controlled by three linked genes. Wildtype plants are normal height with pointed, green leaves. Triple mutant plants are dwarf (d) with round (r), white (w) leaves. A female heterozygous for all three mutations is testcrossed and the following progeny phenotypes were observed:
wildtype
116
dwarf
350
dwarf, round
4
dwarf, round, white
120
round, white
325
round
35
white
3
dwarf, white
47
a. What are the parental genotypes?
b. Which gene is in the middle?
c. Construct a genetic map showing distances between adjacent genes.
d. Calculate the interference observed in this cross.
wildtype
116
dwarf
350
dwarf, round
4
dwarf, round, white
120
round, white
325
round
35
white
3
dwarf, white
47
Explanation / Answer
Answer:
Explanation:
a. What are the parental genotypes?
Female: dRW/Drw
Male: drw/drw
b. Which gene is in the middle? Gene "r""
c. Construct a genetic map showing distances between adjacent genes.
d----------24.3cM----------r-------8.9cM--------w
d.. Calculate the interference observed in this cross: 0.68
Hint: Always recombinant genotypes are smaller than the non-recombinant genotypes.
Hence, the parental (non-recombinant) genotype is dRW / Drw.
Wildtype (DRW)
116
Dwarf (dRW)
350
dwarf, round (drW)
4
dwarf, round, white (drw)
120
round, white(Drw)
325
Round(DrW)
35
White(DRw)
3
dwarf, white(dRw)
47
1).
If single crossover occurs between d & R..
Normal combination: dR / Dr
After crossover: dr/Dr
dr progeny= 4+120=124
DR progeny = 3+116=119
Total this progeny = 243
The recombination frequency between d&R = (number of recombinants/Total progeny) 100
RF = (243/1000)100 = 24.3%
2).
If single crossover occurs between R & W..
Normal combination: RW / rw
After crossover: Rw/rW
Rw progeny= 3+47=50
rW progeny = 4+35=39
Total this progeny = 89
The recombination frequency between R&W = (number of recombinants/Total progeny) 100
RF = (89/1000)100 = 8.9%
3).
If single crossover occurs between d & W..
Normal combination: dW / Dw
After crossover: dw/DW
dw progeny= 120+47=167
DW progeny = 116+35=151
Total this progeny = 318
The recombination frequency between d&W= (number of recombinants/Total progeny) 100
RF = (318/1000)100 = 31.8%
Recombination frequency (%) = Distance between the genes (cM)
d----------24.3cM----------r-------8.9cM--------w
Expected double crossover frequency = (RF between h & w) * (RF between w & b)
= 24.3% * 8.9% = 0.022
The observed double crossover frequency = 3+4 / 1000 = 0.007
Coefficient of Coincidence (COC) = Observed double crossover frequency / Expected double crossover frequency
= 0.007 / 0.022
= 0.32
Interference = 1-COC
= 1-0.32 = 0.68
Wildtype (DRW)
116
Dwarf (dRW)
350
dwarf, round (drW)
4
dwarf, round, white (drw)
120
round, white(Drw)
325
Round(DrW)
35
White(DRw)
3
dwarf, white(dRw)
47
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.