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Exam 5: Genetic Linkage and Mapping in Eukaryotes

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Question 1

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When constructing a genetic map of Zea mays, Creighton and McClintock used genetic markers as well as structural differences in the homologous copies of chromosome 9 that can be seen under the microscope. What are these structural differences called?

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Question 2

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There are three genes located in the gene order A-B-C on a chromosome. Would you expect the recombination frequency to be higher between A and B or A and C?

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Question 3

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In a dihybrid cross exhibiting complete genetic linkage, what would you expect?

What is observed when syntenic genes are close enough to one another that they are unable to assort independently?

Describe the three types of tetrads that can be formed when a diploid yeast sporulates to form haploid gametes.

What ratios of these three tetrads would you expect to see if two genes are linked? Why is each type of tetrad more or less common? What ratios would you expect to see if the two genes are unlinked? Why?

What type of test would you use to determine the relative order of more than two genes?

You perform a test cross of the dihybrid AaBb and score the phenotypes of 1000 progeny. Assuming independent assortment, how many of the progeny do you expect to display the dominant phenotype for both the A and B genes?

For a given haplotype, the frequencies of alleles for gene Y are Y = 0.65 and Y' = 0.35, and the frequencies at gene Z are Z = 0.25 and Z' = 0.75. What is the predicted frequency of the Y'Z' haplotype?

Incomplete genetic linkage is far more common than complete linkage. What is the term for gametes produced when recombination shuffles the alleles of linked genes?

Morgan realized that Bateson and Punnett had detected genetic linkage but they couldn't explain their results because they performed the wrong cross. What type of cross did Morgan use for the analysis of genetic linkage of autosomal genes in Drosophila?

If there is a maximum Lod score of 4.2 at θ = 0.31, what can you say about the linkage and the distance between two genes?

What type of test would you use to determine whether observed data constitute evidence of genetic linkage or are simply a case of chance variation from expected values?

Refer to this map to answer the questions: a)What is the distance between gene E and gene F? b)Assuming I = 0, what is the probability of no crossovers between gene D and gene E? c)Assuming I = 0, what is the probability of no crossovers between gene E and gene F? d)Considering both gene pairs, what is the proportion of nonrecombinant gametes? e)What is the predicted frequency of each parental gamete (DEF/def )? f)What is the recombination frequency between gene D and gene E? g)What is the recombination frequency between gene E and gene F? h)What is the frequency of two single recombinant gametes between genes D and E? i)What is the frequency of two single recombinant gametes between genes E and F? j)What is the frequency of each of the double-recombinant gametes, DeF and dEf? k)Fill in the blanks below to prove that the sum of the frequencies of the eight predicted gamete genotypes is equal to 1.0: _______ + _______ + _______ + _______ + _______ + _______ + _______ + _______ = 1 DEF def Def dEF DEf deF DeF dEf

Recombination frequency differs between males and females. Which sex has a higher rate of recombination, heterogametic (males)or homogametic (females)?

In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg) . The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F₁ progeny had a WT phenotype. The recombination frequency between the two genes is 10%. If an F₁ individual was test crossed, what percentage of the progeny would you expect to have the WT phenotype?

Syntenic genes can assort independently when __________.

Genes A and B are located 10cM from each other on a chromosome. Gene C is located 25cM from gene A and 15cM from gene B. Assuming that I = 0, what is the probability that the trihybrid ABC/abc will produce an ABC gamete?

For a given cross, the expected number of double recombinants is 20 and the observed number of double recombinants is 15. What is the interference calculation (I) ?

Recombination frequency between linked genes increases as the distance between genes gets larger or gets smaller?