1. How many progeny did you look at for this experiment? 2. Which locus is in th

Question

1. How many progeny did you look at for this experiment?

2. Which locus is in the center? (a. tendril size, b. fruit color, c. unable to determine, or d. time to fruit)

Three linked autosomal loci were studied in cucumbers: fruit color (dark vs. light), tendril size (long vs. reduced) and fruiting (normal vs. earlv). 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 Color Number Normal Normal Early Early Early Early Normal Normal Long Long Long Long Reduced Reduced Reduced Reduced Dark Light Light Dark Dark Light Light Dark 421 32 799 28 27 367 968 Use the map to answer the questions below Tendril Size Locus B Locus C R1 R2

Explanation / Answer

From the given table the answers are as follows:

1. We looked at 2675 progeny. (By adding the number of progeny given).

2. c.

We are unable to determine the locus in center.

This is because of the double crossvers given. For any given data we find the locus in middle by using the parental genotypes (which are highest in frequency) and double crossovers (which are the ones in lowest frequency). This is because the middle allele is moved from 1 sister chromatid to another by the event of double crossover. So we observe that the non parental allele of middle gene is flanked by the parental alleles of other genes.

In this case the parental genotypes are Early long light 799 and normal reduced dark 968

The double crossovers are Early long dark 28 and early reduced dark 27.

Suppose allele for Early is given by E, normal by e, long by L, reduced by l, Light by Li and dark by li.

The parental genotypes will be ELLiand elli

The double crossovers will be ELli and Elli.

ELli - 28

Elli- 27

Remember that parental alleles were ELLiand elli. Here in obe double crossover the parental alleles E and L are present with recessive allele li but the second crossover does not have non parental allele of one gene with parental alleles of other genes. Hence, we are unable to determine the locus in center.

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