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Recombinant classes, genotypes and linkage arrangements

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I need help with the following problem set. Please give a detailed set of answers to better assist me with understanding the genetic concepts.

Dihybrid test crosses are made between each pairwise combination of the three genes C, D, and E with the following results:

CD: 222 CE: 48 DE: 198
Cd: 280 Ce: 455 De: 289
cD: 280 cE: 445 dE: 311
cd: 218 ce: 52 de: 202
___________________________
1000 1000 1000 total

15. Which are the recombinant classes in these three crosses?

16. Give the genotypes of the dihybrids in these three crosses, showing linkage arrangements.

17. Draw the map for these three genes, indicating the order and the lengths of the intervals in map units.

18. What can you say about crossover interference based on this data set?

19. Why do the map distances not add up?

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Solution Preview

Please see the attached file.

A test cross involves crossing a heterogygous genotype with a homozygous one. Dihybrid refers to the fact that we are looking at a test cross for two genes at a time. For another example see http://www.saburchill.com/IBbiology/chapters03/008.html

The given crosses include:
CcDdxccdd
CcEexccee
DdEexddee

To yield:
CD: 222 CE: 48 DE: 198
Cd: 280 Ce: 455 De: 289
cD: 280 cE: 445 dE: 311
cd: 218 ce: 52 de: 202
___________________________
1000 1000 1000 total

In the first cross of CcDdxccdd we would expect:

CD cD Cd cd
cd CcDd ccDd Ccdd ccdd
cd CcDd ccDd Ccdd ccdd
cd CcDd ccDd Ccdd ccdd
cd CcDd ccDd Ccdd ccdd

There should be an even ratio of the four genotypes and in our test cross there ...

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Genetics Problems

1.) In guinea pigs, black (B) is dominant to brown (b), and dolid color (S) is dominant to spotted (s). A heterozygous black, solid-colored pig is mated with a brown, spotted pig. The total offspring for several litters are black solid=16, black spotted=5, brown solid=5, and brown spotted=14.

Are these genes linked or unlinked? If they are linked, how many map units are they apart?

2.) A woman is a carrier for a sex-linked lethal gene that causes an embryo with the gene to spontaneously abort. She has nine children. How many of these do you expect to be boys?

3.) A dominant sex-linked gene B produces white bars on black chickens, as seen in the Barred Plymouth Rock breed. A clutch of chicks has equal numbers of black and barred chicks. (Sex is determined by the Z-W system in birds: ZZ are males, ZW are females.)
a.) If only the females are found to be black, what were the genotypes of the parents?
b.) If males and females are evenly represented in the black and barred chicks, what were the genotypes of the parents?

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