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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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Which type of crossover event produces no recombinant chromosomes?


A) single-strand crossover
B) two-strand double crossover
C) three-strand double crossover
D) four-strand double crossover
E) None of the above;all crossover events produce recombinant chromosomes.

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

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The syntenic genes A and Z are linked.A cross between two parents,AAZZ and aazz,produces F₁ progeny with the AaZz genotype.What are the possible arrangements of alleles on the F₁ progeny's chromosomes?


A) AZ/az
B) Az/aZ
C) Aa/Zz
D) AZ/Az or az/aZ
E) A/Z or a/z

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

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If too little time has passed for crossing over to randomize haplotypes or if natural selection favors certain haplotypes,what type of linkage would you expect to see?

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linkage di...

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Assuming three genes are linked,how many recombinant genotypes would you expect and at what frequency?


A) two recombinant genotypes,more frequent than expected by chance
B) four recombinant genotypes,more frequent than expected by chance
C) six recombinant genotypes,more frequent than expected by chance
D) four recombinant genotypes,less frequent than expected by chance
E) six recombinant genotypes,less frequent than expected by chance

F) B) and C)
G) D) and E)

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


A) one parental allele combination occurring more frequently than another
B) two equally frequent gametes containing only parental allele combinations
C) only recombinant gametes
D) one parental allele combination occurring more frequently than another and no recombinant gametes
E) two equally frequent gametes containing only parental allele combinations and no recombinant gametes

F) All of the above
G) C) and D)

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For a given cross,the expected number of double recombinants is 20 and the observed number of double recombinants is 15.What is the coefficient of coincidence (c) ?


A) 0.25
B) 1.33
C) 20
D) 0.75
E) 15

F) A) and B)
G) A) and D)

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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?


A) test cross
B) two-point test-cross
C) three-point test-cross
D) chi-square analysis
E) recombination frequency (r) calculation

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

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Crossing over occurs frequently during meiosis.Can crossing over occur during mitosis? Explain why mitotic crossing over may or may not be possible.

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Mitotic crossover is a rare event.Mitoti...

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Which type of crossover event produces all four recombinant chromosomes?


A) single-strand crossover
B) two-strand double crossover
C) three-strand double crossover
D) four-strand double crossover
E) None of the above;all crossover events produce a combination of parental and recombinant chromosomes.

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

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Describe the three types of tetrads.

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Parental ditypes (PD)contain four haploi...

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The alleles of syntenic genes can be reshuffled by crossing over between homologous chromosomes to produce ________.

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recombinan...

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

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linked and...

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In early genetic analysis,5% recombination is equal to ________ map unit(s)(m.u.)or centimorgan(s)(cM)of distance between linked genes.

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Bateson and Punnett saw early evidence of gene linkage.What terms did they use to describe genes that remained together frequently and the loss of parental alleles in favor of new,nonparental phenotypes in the F₂ progeny?

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coupling a...

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Tetrad analysis can be used to identify genetic linkage in haploid eukaryotes. Parental and recombinant gametes contained in an ascus can be analyzed to map genes. -What ratios of these three tetrads would you expect to see if two genes are linked or unlinked? Why is one type of tetrad more or less common?

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If two genes are linked,you will see tha...

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

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homogameti...

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Which type of crossover event produces two parental and two recombinant chromosomes in gametes?


A) single-strand crossover
B) two-strand double crossover
C) three-strand double crossover
D) four-strand double crossover
E) None of the above;all crossover events produce only recombinant chromosomes.

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

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The Huntington disease (HD) allele was discovered


A) by mapping it to blood enzyme genes,based on Lod scores of -2.
B) through pedigree analysis alone.
C) by linkage to a DNA genetic marker,D4S10 with a Lod score of 8.53.
D) through mapping to known homologs in other organisms such as mice.
E) through direct sequencing of mutations identified by SNPs.

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

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What organism exhibits complete genetic linkage,meaning there is no recombination between homologous chromosomes?

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male Droso...

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