Question

5. Deletions can be used to map genes along a chromosome. In order to do this a series of crosses in which one parent is homozygous for a mutant allele is crossed with the other parent that is homozygous for a partial deletion of the region. The progeny are scored to determine whether they have the mutant phenotype ("m") or the wild-type phenotype ("+"). If the mutant allele falls within the deletion it will have the "m" phenotype, if it falls outside the deletion it will complement and have the ("+") phenotype. Some of the deletions will take out more than one gene that are next to each other and thus will produce the "m" phenotypes with several of the genes in question. Use the following table of progeny phenotypes for 7 different deletions to determine the order of the genes a-g on the chromosome.

	mutations
deletion	a	b	c	d	e	f	g
1	+	+	+	m	m	+	+
2	+	+	m	m	+	+	+
3	+	m	+	+	+	m	+
4	+	m	m	m	m	+	+
5	m	m	+	+	+	m	+
6	+	m	m	m	m	m	m
7	+	+	+	m	m	+	m

a.	cabgdfe
b.	dgcbafe
c.	gedcbfa
d.	afdegcb
e.	ebdgafc

Answer 1

genes that does not complement with the deletion produces mutant phenotype.

deletion	the gene that does not complement with the deletion
1	d,e
2	c,d
3	b,f
4	b,c,d,e
5	a, b, f
6	b,c,d,e,f,g
7	d,e,g

for mutation1 d and e do not complement, means d and e are close together and deleted.

c and d do not complement with deletion 2 means c and d are close together and deleted.

b and f do not complement with deletion 3 means b and f are close together and deleted.

b,c,d,e do not complement with deletion 4 means b,c,d,and e are close together and deleted.

a, b, f do not complement with deletion 5 means a, b and f are close together and deleted.

b,c,d,e,f,g do not complement with deletion 6 and b,c,d,e,f,g  are close together and deleted

d,e,g do not complement with deletion 7 and d,e,g are close together and deleted.

by analysing all these the order of the genes afbcdeg.

(d and e are close together, and c and d are close together so the order is cde, from 6 and 7 e and g are close together so the order is cdeg, from 4 b is close to c, so adding b to the sequence, bcdeg, from 5 and 6 f is close to b, adding f to the sequence the order is fbcdeg, from 5 a is close to b so the order is afbcdeg)

so the answer is c) gedcbfa