Question

You are studying recessive mutations of three autosomal, linked genes in guinea pigs: fur color (y, yellow); fur texture (wv, wavy); ear size (l, large). The data in columns A and B was obtained from crosses of heterozygous F1 females with homozygous testcross males (recessive for all three traits).

Column: A             B                      C                     D                        E

F2 Phenotype	# Observed	Corresponding Genotype	P or SCO or DCO	Genotype Written in Correct Order on Homologs
yellow	310	ywv+l+	P
wildtype	32
yellow, wavy	150
wavy, large	320
wavy	16
large	120
yellow, large	14
yellow, wavy, large	38
Total	1000

a) How many sets of reciprocal phenotypes are shown? ____________________

b) In Column C, list the corresponding genotype. Account for all three traits. The first one has been provided for you as an example. For all answers in column C, use the order of traits: fur color, fur texture, ear size.

c) Indicate the type of each homolog in Column D: parental P, single crossover SCO, or double crossover DCO. The first one has been provided for you as an example.

d) On this form below or on blank paper to be submitted with this form, determine the correct order of all three genes. All work must be shown for credit. Fill in Column E above.

Answer 1

E- The distance between yellow and large

If we want to find the distance between the y and l then we need to find out the crossover frequency and divide it by the total number of progeny

y+ l+ wv+ 32

y l wv 38

y+ l+ wv 16

y l wv+ 14

Linkage distance = total number of recombinant * 100 / total number of progeny

100 * 100/ 1000

= 10

So, map distance between yellow and large is 10 map units or 10cM

The distance between yellow and wavy.

If we want to find the distance between the wv and l then we need to find out the crossover frequency and divide it by the total number of progeny

y+ l+ wv 16

y l wv+ 14

y l+ wv 150

y+ l wv+ 120

Linkage distance = total number of recombinant * 100 / total number of progeny

300*100/ 1000

= 30

So, map distance between wv and l is 30 map units or 30cM