Consider a plant species: • Elongated seeds (E) are dominant over round (e). • R
ID: 67876 • Letter: C
Question
Consider a plant species:
• Elongated seeds (E) are dominant over round (e).
• Rough bark (R) is dominant over smooth (r).
• Yellow flowers (Y) are dominant over white (y).
A trihybrid (Ee Rr Yy) plant is testcrossed (= crossed to an ee rr yy plant) and the following progeny are obtained:
Question 4.
Fill in the table on your handout by determining the genotypes of the gametes each phenotypic class received from the trihybrid parent.
As best as you can using these data, determine linkage (including map distance) for the genes, and also determine the phase of the parent plant’s alleles and answer questions 5 to 8. Hint: start by looking at two loci at a time to determine their linkage relationship. Are they linked? At what map distance? One strategy is to add the number of gametes that receive the same alleles for two loci. For example, two classes of progeny received an ER gamete. You can add these two classes to get the total number of ER gametes. Using this approach, you can determine whether there is a deviation from a 1:1:1:1 ratio predicted by independent assortment. If so, which gametes are more abundant? Less abundant?
Question 5.
Are the loci E and R linked? If so, at what map distance?
Question 6.
Are the loci R and Y linked? Is so, at what map distance?
Question 7.
Are the loci E and Y linked? If so, at what map distance?
Question 8.
What is the phase of the trihybrid parent plant's alleles?
Phenotype Genotype of gamete received from the trihybrid parent # of progeny Elongated, rough, yellow 9 Elongated, rough, white12 Elongated, smooth, yellow
238 Elongated, smooth, white
237 Rounded, rough, yellow
243 Rounded, rough, white
242 Rounded, smooth, yellow
9 Rounded, smooth, white
10
Explanation / Answer
total number of offspring =1000
Question 5.
Are the loci E and R linked? If so, at what map distance?
Answer:
calculate crossing over frequency, if it exceeds 50% then alleles are not linked, and 1% crossing over = 1mu or 1cm
crossing over % = number of recombinants/total number of offsprings
(238+237+243+242)/1000
960/1000= 96%
so E and R loci are not linked and map distance = 96 mu
Question 6.
Are the loci R and Y linked? Is so, at what map distance?
Answer:
calculate crossing over frequency, if it exceeds 50% then alleles are not linked, and 1% crossing over = 1mu or 1cm
crossing over % = number of recombinants/total number of offsprings
12+238+242+9 = 501
crossing over % = 50.1%
so Y and R loci are not linked and map distance = 50.1 mu
Question 7.
Are the loci E and Y linked? If so, at what map distance?
Answer:
calculate crossing over frequency if it exceeds 50% then alleles are not linked, and 1% crossing over = 1mu or 1cm
crossing over % = number of recombinants/total number of offsprings
12+237+243+9 = 501
crossing over % = 50.1%
so E and Y loci are not linked and map distance = 50.1 mu?
Question 8.
What is the phase of the trihybrid parent plant's alleles?