Time for some more xenobiology. In aliens, glossy exoskeleton (G) is dominant to

Question

Time for some more xenobiology. In aliens, glossy exoskeleton (G) is dominant to dull exoskeleton (g), excessive drooling (D) is dominant to normal drooling (d), and highly acidic blood (A) is dominant to mildly acidic blood (a). Genetic researchers at Weyland-Yutani Corporation perform a three-point testcross to map the relative locations of these genes. They crossed heterozygotes for all three traits with recessive homozygotes and collect this data:

Observed Number

Glossy, excessive drooling, highly acidic

GDA/gda

Dull, normal drooling, mildly acidic

gda/gda

Glossy, excessive drooling, mildly acidic

GDa/gda

Dull, normal drooling, highly acidic

gda/gda

Glossy, normal drooling, highly acidic

GgA/gda

Dull, excessive drooling, mildly acidic

gDA/gda

Glossy, normal drooling, mildly acidic

Gda/gda

Dull, excessive drooling, highly acidic

GDA/gda

A. Which progeny are the nonrecombinants?

B. Which progeny are the double crossovers? What is the gene order?

Observed Number

Glossy, excessive drooling, highly acidic

GDA/gda

43

Dull, normal drooling, mildly acidic

gda/gda

36

Glossy, excessive drooling, mildly acidic

GDa/gda

13

Dull, normal drooling, highly acidic

gda/gda

4

Glossy, normal drooling, highly acidic

GgA/gda

333

Dull, excessive drooling, mildly acidic

gDA/gda

303

Glossy, normal drooling, mildly acidic

Gda/gda

130

Dull, excessive drooling, highly acidic

GDA/gda

138 Total 1000

Explanation / Answer

Given :

Observed Number

Glossy, excessive drooling, highly acidic

GDA/gda

Dull, normal drooling, mildly acidic

gda/gda

Glossy, excessive drooling, mildly acidic

GDa/gda

Dull, normal drooling, highly acidic

gda/gda

Glossy, normal drooling, highly acidic

GgA/gda

Dull, excessive drooling, mildly acidic

gDA/gda

Glossy, normal drooling, mildly acidic

Gda/gda

Dull, excessive drooling, highly acidic

GDA/gda

The most abundant genotypes are the partenal types. These genotypes are GgA and gDA

Tthe least frequent genotypes are the double-crossover geneotypes , these are GDa and gda.

In the double-crossover genotypes, which parental allele is not associated with the two parental alleles it was associated with in the original parental cross. From the first double crossover, GDA the g allele is associated with the G and A alleles, two alleles it was not associated with in the original cross. Therefore, D is in the middle, and the gene order is G D A.

Observed Number

Glossy, excessive drooling, highly acidic

GDA/gda

43

Dull, normal drooling, mildly acidic

gda/gda

36

Glossy, excessive drooling, mildly acidic

GDa/gda

13

Dull, normal drooling, highly acidic

gda/gda

4

Glossy, normal drooling, highly acidic

GgA/gda

333

Dull, excessive drooling, mildly acidic

gDA/gda

303

Glossy, normal drooling, mildly acidic

Gda/gda

130

Dull, excessive drooling, highly acidic

GDA/gda

138 Total 1000

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