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Exam 14: Genetic Mapping in Eukaryotes

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Question 21

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X, Y, and Z are linked genes. Based on testcross data, the frequency of recombination between genes X and Y was determined to be 33.1 map units. Between genes X and Z, the distance was 11.8 mu; between genes Y and Z, the distance was 21.3 mu. -What is the order of these three genes on the chromosome?

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Question 22

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If an AABB strain is mated with an aabb strain,an AB gamete produced by the resulting F₁ is

A) impossible.
B) parental.
C) recombinant.
D) the most common.
E) None of these

F) A) and E)
G) C) and D)

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Question 23

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A coefficient of coincidence of zero is the same as an interference value of zero.

Testcrosses may be used to determine if two genes are linked.

If in calculating the distance between two genes using data from a testcrossed dihybrid you arrive at a genetic distance of 70 map units,there is likely to be something wrong with your calculations,the experimental data,or with the experiment itself.

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. $\begin{array} { l r } + + + & 669 \\a b c & 653 \\+ + c & 121 \\a b + & 139 \\+ b + & 2280 \\a + c & 2215 \\+ b c & 3 \\a + + & 2\end{array}$ -Which gene pair is closer together; i.e.there are fewer map units between them?

What is the difference in the likelihood of linkage between two genes with a lod score of 2 and two genes with a lod score of 3?

X, Y, and Z are linked genes. Based on testcross data, the frequency of recombination between genes X and Y was determined to be 33.1 map units. Between genes X and Z, the distance was 11.8 mu; between genes Y and Z, the distance was 21.3 mu. -Of the three pairs of genes,which ones are closest to each other and which ones are farthest apart?

A red,round,true-breeding tomato is bred with a yellow,oval,true-breeding tomato,and the F₁s are testcrossed to a homozygous-recessive tester.This results in the offspring below.Calculate the chi-squared value to test the likelihood of linkage. $\begin{array} { l r } \text { yellow oval } & 11 \\\text { red round } & 14 \\\text { yellow round } & 7 \\\text { red oval } & 8\end{array}$

Genes may show 50% recombination either when the genes are on different chromosomes or when the genes are far apart on the same chromosome.

If genes are linked and an F₁ is testcrossed,

What does the chi-square test tell us about the linkage of two genes?

The closer together two genes are on a chromosome,

Explain how Curt Stern showed,using evidence from Drosophila,that genetic recombination is associated with the physical exchange of parts between homologous chromosomes.

Why does the recombination frequency often lead to an underestimation of the true map distance between linked genes?

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. $\begin{array} { l r } + + + & 669 \\a b c & 653 \\+ + c & 121 \\a b + & 139 \\+ b + & 2280 \\a + c & 2215 \\+ b c & 3 \\a + + & 2\end{array}$ -The cross represented by a^+b+c+/abc × abc/abc is

A linkage map illustrates the exact physical locations of genes on a chromosome.

A chi-square analysis of linkage between genes k and f produces a P value of 0.99.What is the likelihood that these two genes are linked?

Please select the best match for each term.

T.H.Morgan and his colleagues found that among the offspring of genetic crosses,parental phenotypic classes were the most frequent,while recombinant classes occurred less frequently.This observation led Morgan to conclude that