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Exam 7: Linkage, Recombination, and Eukaryotic Gene Mapping

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Question 1

Multiple Choice

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Lod scores measure:

A) the relatedness of two individuals.
B) the number of crossover events that occur along an entire chromosome.
C) how often double crossovers occur.
D) the length of a linkage group.
E) the likelihood of linkage between genes.

F) A) and B)
G) None of the above

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Question 2

Multiple Choice

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Assume that you are able to examine a total of 100 separate meiotic events in an animal species. You note that within 10 of these meiotic events, there was a crossover event occurring between genes A and B. In the remaining 90 events there was no crossover event between these two genes. What would be the expected map distance between genes A and B?

A) 10 m.u.
B) 5 m.u.
C) 20 m.u.
D) 45 m.u.
E) 50 m.u.

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

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B

Question 3

Multiple Choice

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Linked genes are:

In addition to determining genotypes, two- and three-factor testcrosses can be used to:

Recombination frequencies can be calculated by:

A series of two-point crosses among fruit flies is carried out between genes for brown eyes (bw) , arc wings (a) , vestigial wings (vg) , ebony body color (e) , and curved wings (cv) . The following number of nonrecombinant and recombinant progeny were obtained from each cross: $\begin{array} { | l l | l | } \hline \text { Genes in cross } & \text { Progeny (NR) } & \text { Progeny (R) } \\\hline a , b w & 2224 & 117 \\\hline a , c v & 2609 & 823 \\\hline a , e & 3200 & 3200 \\\hline a , v g & 5172 & 2379 \\\hline b w , c v & 4614 & 1706 \\\hline b w , e & 4150 & 4150 \\b w , v g & 2796 & 1434 \\c v , e & 3116 & 3116 \\c v , v g & 2102 & 305 \\v g ~ e & 4559 & 4559 \\\hline\end{array}$ Using these data from two-point crosses, what it the best genetic map (in m.u.) that can be developed?

A testcross is performed on an individual to examine three linked genes. The most frequent phenotypes of the progeny were Abc and aBC, and the least frequent phenotypes were abc and ABC. What was the genotype of the heterozygous individual that is test-crossed with the correct order of the three genes?

Assume that an individual of AB/ab genotype is involved in a testcross and four classes of testcross progeny are found in equal frequencies. Which of the following statements is TRUE?

Use the following to answer questions You are doing lab work with a new species of beetle. You have isolated lines that breed true for either blue shells and long antenna or green shells and short antenna. Crossing these lines yields F₁ progeny with blue shells and long antenna. Crossing F₁ progeny with beetles that have green shells and short antenna yields the following progeny: Blue shell, long antenna82 Green shell, short antenna78 Blue shell, short antenna37 Green shell, long antenna43 Total240 -A chi-square test is done to test for independent assortment. What is the resulting chi-square value and how many degree(s) of freedom should be used in its interpretation?

Use the following to answer questions You are doing lab work with a new species of beetle. You have isolated lines that breed true for either blue shells and long antenna or green shells and short antenna. Crossing these lines yields F₁ progeny with blue shells and long antenna. Crossing F₁ progeny with beetles that have green shells and short antenna yields the following progeny: Blue shell, long antenna82 Green shell, short antenna78 Blue shell, short antenna37 Green shell, long antenna43 Total240 -Assuming that the genes are linked, what is the map distance between them in m.u.?

A physical map often measures _____, whereas a genetic map measures _____.

Is it possible for two different genes located on the same chromosome to assort independently?

The map distances for genes that are close to each other are more accurate than map distances for genes that are quite far apart because:

If a three-strand double crossover occurs between two genes during meiosis, what is the expected outcome with respect to these two genes?

In flower beetles, pygmy (py) is recessive to normal size (py⁺) , and red color (r) is recessive to brown (r⁺) . A beetle heterozygous for these characteristics was test-crossed to a beetle homozygous for pygmy and red. The following are progeny phenotypes from this testcross. $\begin{array} { l l r } p y ^ { + } & r ^ { + } & 180 \\p y ^ { + } & r & 22 \\p y & r ^ { + } & 19 \\p y & r & 191 \\\text { Total } && 412\end{array}$ Carry out a series of chi-square tests to determine if there is equal segregation of alleles at the py locus. - What is the correct chi-square value and how many degree(s) of freedom should be used in its interpretation?

Two linked genes, (A) and (B) , are separated by 18 m.u. A man with genotype Aa Bb marries a woman who is aa bb. The man's father was AA BB. What is the probability that their first child will be Aa bb?

GGHH and ccdd individuals are crossed to each other and the F₁ backcrossed to the gghh parent. The 4000 progeny included 1806 GgHh, 1794 gghh, 196 Gghh, and 204 ggHh individuals. GGhh and ggHH individuals are next crossed to each other and the F₁ test-crossed to a gghh individual. A total of 1600 offspring appeared in the progeny. How many do you expect to be of GgHh genotype?

Use the following to answer questions : You just bought two black guinea pigs, one male and one female, of the same genotype from the pet store that are known to be heterozygous (Bb) . You also know that black fur (BB) is dominant over white fur (bb) and that a lethal recessive allele is located only 1 m.u. away from the recessive b allele, and your animals are both heterozygous for this gene also. -What is the probability of finding a white individual among the progeny if you cross these two animals?

A situation in which the coefficient of coincidence is greater than 1.0 would indicate that:

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?