Use the map to answer the questions below Tendril Size Locus

Use the map to answer the questions below.

Tendril Size

Locus B

Locus C   

Which locus is in the center?

Time to Fruit	Tendril Size	Fruit Color	Number
Normal	Long	Dark	351
Normal	Long	Light	32
Early	Long	Light	960
Early	Long	Dark	28
Early	Reduced	Dark	22
Early	Reduced	Light	487
Normal	Reduced	Light	35
Normal	Reduced	Dark	959

Three linked autosomal loci were studied in cucumbers: fruit color (dark vs. light), tendril size (long vs. reduced) and fruiting (normal vs. early). Pure breeding early fruiting light cucumbers with long tendrils were mated to pure breeding normal fruiting dark cucumbers with reduced tendrils. The F1 were testcrossed and the testcross progeny are given below. Time to Fruit Tendril Size Fruit Colo Number Dark Normal 351 Long Normal Light 32 Long Early Long Light 960 Early Dark 28 Long Early Reduced Dark Early Reduced Light 487 Normal Reduced Light 959 Normal Reduced Dark Use the map to answer the questions below. Tendril Size Locus C Locus B R2

Solution

We need to consider that more the distance between the genes more will be crossing over or more will be the recombinants, less the distance, less will be recombinants.

Assign the genes with alphabets. Tendril size: Reduced (R) vs Long (r); Fruiting: Normal (N) vs Early (n); Fruit colour: Dark (D) vs Light (d). As the question says F1 is test crossed, means Tendril size reduced will be dominant over long or the dominant genes are on the same chromosome and recessive ones are on different chromosomes. (cis configuration= RND/rnd).

According to the outcomes, consider the highest recombinant number: 960 (Early, long and light= rnd) and 959 (Normal, Reduced and Dark=RND). This says that they are of parental types.

Now consider Single cross (Rnd=Early reduced light) = 487

rND (Normal Long Dark)=351

RNd (Normal Reduced light)=35

rnD (Early Long Dark)=28

Rnd and rND have more no of recombinants, means R and N are spaced distantly

and double cross overs rNd (Normal Long Light)=32

RnD (Reduced Early Dark)=22

Calculate percent Recombination between R and N = 487+351+22+32 = 892

Total No of outcomes = 2874

Therefore, % recomb=892/2894 x 100 = 31.03% or 31.03 cM

% recombination between N and D= 35+28+22+32=117

% recombination = 117/2874 x 100 = 4.07% or 4.07 cM

Total distance between R and D is 31.03cM + 4.07 cM = 35.1 cM

To conclude, fruiting locus will be in the center and colour of fruit will be in the end.

The R1 distance is 31.03 cM and R2 is 4.07 cM.