1 What is the correct gene order a obt sp p b obt p sp c p o

1. What is the correct gene order?

a) obt sp p

b) obt p sp

c) p obt sp

d) cannot be determined

2. Which genes are most likely to travel together?

a) genes on homologous chromosomes

b) genes on the same chromosome

c) genes separated by the smallest distance, in map units, on the same chromosome

d) genes at the opposite tips of the same chromosome

3. In a three-point cross, which group is the double crossovers?

the largest proportion

the smallest proportion

C) There are no double crossovers in a three-point cross.

the sum of the single crossovers

4. In a testcross between a y with the recessive traits a and b and a y heterozygous for these traits, all the o spring are either wild type or exhibit both recessive traits. is suggests that the loci for traits a and b are:

unlinked

b) more than 50 map units apart.

completely linked.

d) Linkage information cannot be inferred from this result.

5. In a testcross between a fly that is a+b+c+ and heterozygous at all three loci and a fly that is a b c, the smallest phenotypic class is a+b c. What is the order of these genes on the chromosome?

a b c

a c b

b a c

c b a

		a) genes on homologous chromosomes
		b) genes on the same chromosome
		c) genes separated by the smallest distance, in map units, on the same chromosome
		d) genes at the opposite tips of the same chromosome 3. In a three-point cross, which group is the double crossovers? A) the largest proportion B) the smallest proportion C) There are no double crossovers in a three-point cross. D) the sum of the single crossovers

On chromosome 3 in Drosophila, there are the following mutations: The obtuse wing (obt) mutation is recessive. It causes abnormally shaped wings. Spineless bristles is another recessive mutation, resulting in bristles without spines on the fly\'s body. .Pink eyes is a third recessive mutation, producing flies with pink eyes. The female from the previous cross, who happens to be heterozygous for all three mutations, was mated to a male homozygous for all three mutations. The following data were obtained from this mating (out of a total of 1000 progeny): Pheno Number 49 obt.s 44 obt st 94 obt st 99 obt s 344 obt s 358 obt.s obt.s obt s

Solution

1. obt, sp, p- p allele is associated with the obt and the sp allele, which it was not associated in the original cross, therefore obt, sp , is the gene order.

2. C

3B

4 A

5D