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640 Chapter 19 NEL

(a) Circle the areas of the chromatids that show crossing

over.

(b) Using the diagram above, which genes appear

farthest apart? (Choose from EF,FG,or EG.)

(c) Which alleles have been exchanged?

2. In 1913, Sturtevant used crossover frequencies of
   Drosophilato construct chromosome maps. To
   determine map distances, he arbitrarily assigned one
   recombination for every 100 fertilized eggs. For
   example, genes that had a crossover frequency of
   15 % were said to be 15 units apart. Genes that had a
   5 % recombination rate were much closer. These
   genes are 5 units apart.
   (d) Using the data in Table 3, determine the distance
   between genes Eand F.

Analysis

(h) What mathematical evidence indicates that gene F

must be found between genes Eand G?

(i) Draw the gene map to scale. (Use 1 cm to represent

1 unit.)

(j) For a series of breeding experiments, a linkage

group composed of genes W,X,Y,and Z was found

to show the gene combinations in Table 5.(All

recombinations are expressed per 100 fertilized eggs.)

LAB EXERCISE 19.Bcontinued

centromere

G

F

E

G

F

E

g

f

E

G

F

e

g

f

e

g

f

e

homologous

chromosomes

chromatids

Figure 8
Crossing over

Table 3

Cross Offspring Frequency (%)

EF×ef EF+ ef( from parent) 94

Ef+ eF(recombination) 6

Table 4

Cross Offspring Frequency (%)

EF×ef EF+ ef( from parent) 94

Ef+ eF(recombination) 6

EG×eg EG + eg( from parent) 90

Eg + eG( recombination) 10

FG×fg FG+ fg(from parent) 96

Fg+ fG(recombination) 4

Table 5

Genes WX YZ

W -578

X 5- 23

Y 72 -1

Z 83 1-

Table 6

Genes AB CD

A -12154

B 12 - 3 8

C 15 3 - 11

D 4811-

(e) Would the distance between genes eand fbe

identical?

3. Use the data in Table 4to construct a complete gene
   map.
   (f ) What is the distance between genes Eand G?
   (g) What is the distance between genes Fand G?

Construct a gene map. Show the relative positions of

each of the genes along the chromosome and

indicate distances in map units.

(k) For a series of breeding experiments, a linkage

group composed of genes A, B, C,and Dwas found

to show the gene combinations in Table 6.(All

recombinations are expressed per 100 fertilized eggs.)

Construct a gene map. Show the relative positions of

each of the genes along the chromosome and

indicate distances in map units.