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Exam 5: Chromosome Mapping in Eukaryotes

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Question 1

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Based on the classic experiments of Creighton and McClintock with maize,crossing over involves a physical exchange between chromatids.What particular chromosomal characteristic allowed their experiments to succeed?

A) a missing chromosome
B) a chromosome with a unique cytological marker
C) three chromosomes with identical structure
D) colored bands along the lengths of a chromosome
E) an extra chromosome

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

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Question 2

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The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data one can conclude that______ .

A) the recombinant progeny are Ge/Ge and gE/gE
B) the recombinant progeny are gE/ge and Ge/ge
C) the recombinant progeny are GE/GE and ge/ge
D) the recombinant progeny are gE/GE and GE/ge
E) the recombinant progeny are GE/ge and GE/ge

F) A) and B)
G) A) and E)

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Question 3

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In Drosophila,assume that the gene for scute bristles s) is located at map position 0.0 and that the gene for ruby eyes r) is at position 15.0.Both genes are located on the X chromosome and are recessive to their wild-type alleles.A cross is made between scute-bristled females and ruby-eyed males.Phenotypically wild-type F₁ females were then mated to homozygous double mutant males,and 1000 offspring were produced.Give the frequency of scute expected.

In a three-point mapping experiment,how many different genotypic classes are expected?

Assume that the genes for tan body and bare wings are 15 map units apart on chromosome II in Drosophila.Assume also that a tan-bodied,bare-winged female was mated to a wild-type male and that the resulting F₁ phenotypically wild-type females were mated to tan-bodied,bare-winged males.Of 1000 offspring,what would be the expected of wild-type offspring,and in what numbers would they be expected?

Which of the following best describes why mapping is most accurate when genes are close together on a chromosome?

The coefficient of coincidence reflects the frequency of observed double crossovers compared to the frequency of expected double crossovers.What is the relationship between the coefficient of coincidence and interference?

Which of the following statements is true?

If interference is complete,what would be the frequency of double crossovers?

The phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called________ .

The cross GE/ge × ge/ge produces the following progeny: GE/ge 404; ge/ge 396; gE/ge 97; Ge/ge 103.From these data,one can conclude that .

Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb,48 Aabb,52 aaBb,94 aabb.These results are consistent with which scenario described?

The genes for purple eyes and curved wings are approximately 21 map units apart on chromosome II in Drosophila.Assume that a purple-eyed female was mated to a curved wing male and that the resulting F₁ phenotypically wild-type females were mated to purple,curved males.Of 1000 offspring,what would be the expected number of flies with purple eyes and curved wings?

What term is applied when two genes fail to assort independently,that is,they tend to segregate together during gamete formation?

Below is a diagram during crossing over.Describe the outcome.

Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism.If you examined 200 primary oocytes,in how many would you expect to see a chiasma between the two loci mentioned above?

What relatively recent scientific advancement has made mapping by linkage or classical genetic mapping approaches virtually obsolete?

A ____ is all the genes on a single chromosome.

__________occurs when a crossover in one region of a chromosome reduces crossovers in nearby regions.

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body.The F₁ Lobe females were then backcrossed with homozygous smooth abdomen,straw body males,the following phenotypes were observed: Give the map units between Lobe and straw.