Question 1

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

Accepted Answer

Coefficient of coincidence (c) = observed number of double recombinants / expected number of double recombinants
c = 15/20 = 0.75

Question 2

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

Accepted Answer

E

Question 3

When does recombination occur?
A)before DNA replication
B)at the two-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
C)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and before DNA replication
D)at the two-strand stage,when the sister chromatids have been separated,and after DNA replication
E)at the four-strand stage,when each member of a homologous chromosome pair is composed of two sister chromatids,and after DNA replication

Accepted Answer

E

Question 4

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.

Accepted Answer

The answer of Which type of crossover event produces no...

Question 5

Genetic linkage leads to the production of a significantly greater than expected number of gametes containing chromosomes with
A)allele combinations that are different from parental combinations.
B)parental combinations of alleles.
C)mutant alleles.
D)dominant alleles.
E)recessive alleles.

Accepted Answer

Genetic linkage leads to the production of a significant number of gametes containing chromosomes with parental combinations of alleles, which means that the linked genes are inherited together, rather than being separated by independent assortment. Therefore, there will be a higher frequency of parental combinations than expected based on probability.

Question 6

Intragenic recombination can be detected
A)based on recombination between homologs carrying different mutant alleles.
B)by the recovery of 100% double-mutant chromosomes.
C)by the recovery of both wild-type and double-mutant chromosomes.
D)based on recombination between homologs with different mutant alleles and recovery of 100% double-mutant chromosomes.
E)based on recombination between homologs with different mutant alleles and recovery of both wild-type and double-mutant chromosomes.

Accepted Answer

Intragenic recombination can be detected through the recovery of both wild-type and double-mutant chromosomes, which is described by choice E. This is because intragenic recombination involves a crossover event occurring within a single gene, leading to the exchange of genetic material between homologous chromosomes with different mutant alleles. As a result, some offspring will inherit a wild-type allele and a mutant allele from each parent, while others will inherit two mutant alleles. Choice B, recovery of only double-mutant chromosomes, would be indicative of non-recombinant gametes, while choice A, recombination between homologs carrying different mutant alleles, is not necessarily specific to intragenic recombination. Choice D is a combination of A and B and is also not specific to intragenic recombination.

Question 7

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?
A)0.16
B)0.26
C)0.74
D)0.84
E)1.1

Accepted Answer

The predicted frequency of the Y'Z' haplotype is calculated by multiplying the frequencies of Y' and Z', which is 0.35 * 0.75 = 0.2625, approximately 0.26.

Question 8

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

Accepted Answer

The answer of Assuming three genes are linked,how many recombinant...

Question 9

Syntenic genes can assort independently when
A)they are very close together on a chromosome.
B)they are located on different chromosomes.
C)crossing over occurs rarely between the genes.
D)they are far apart on a chromosome and crossing over occurs frequently between the genes.
E)they are far apart on a chromosome and crossing over occurs very rarely between the genes.

Accepted Answer

The answer of Syntenic genes can assort independently when
A)they are...

Question 10

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

Accepted Answer

The answer of For a given cross,the expected number of...

Question 11

Where does crossing over occur?
A)at the centromeres
B)at the telomeres
C)at nodules that occur randomly at "hotspots" along the synaptonemal complex
D)at nodules that occur in specific,evenly spaced locations along a chromosome
E)at both the centromeres and telomeres

Accepted Answer

Crossing over occurs at nodules that occur randomly at "hotspots" along the synaptonemal complex, which is the site of homologous chromosome pairing during meiosis.

Question 12

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

Accepted Answer

The answer of The syntenic genes A and Z are...

Question 13

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.

Accepted Answer

The HD allele was discovered by linkage to a DNA genetic marker, D4S10, with a Lod score of 8.53. This method of discovery involves tracking the cosegregation of a DNA marker with the disease phenotype in families, and the higher the Lod score, the stronger the evidence for linkage between the marker and the disease gene.

Question 14

The alleles of linked genes tend to
A)segregate together during gamete production.
B)assort independently.
C)be mutated more often than unlinked genes.
D)experience a higher rate of crossing over.
E)assort independently and show a higher rate of crossing over.

Accepted Answer

Linked genes are located close to each other on the same chromosome and tend to be inherited together during meiosis, thus segregating together during gamete production. This is known as linkage and can result in the formation of specific combinations of alleles in offspring.

Question 15

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.

Accepted Answer

A four-strand double crossover involves two double-strand breaks and repair by recombination, resulting in the exchange of genetic material between four chromatids. This type of crossover can produce all four recombinant chromosomes.

Question 16

In a two-point test-cross analysis,a dihybrid F₁ fly is crossed to a
A)pure-breeding mate with a dominant phenotype (AABB).
B)pure-breeding mate with a recessive phenotype (aabb).
C)heterozygote mate (AaBb).
D)mate that is dominant for one gene and recessive for the other (AAbb or aaBB).
E)second dihybrid F₁ fly (sibling cross).

Accepted Answer

The best choice for a two-point test-cross analysis is to cross the dihybrid F₁ fly with a pure-breeding mate with a recessive phenotype (aabb). This allows for the observation of independent assortment of the two genes being tested, as all offspring will show the phenotype corresponding to the dominant allele in the dihybrid F₁ fly. If a heterozygote mate (AaBb) or a mate that is dominant for one gene and recessive for the other (AAbb or aaBB) were used, the observed phenotypic ratios would not allow for the determination of independent assortment, as some offspring would show the recessive phenotypes for one or both genes. A sibling cross (choice E) would also not be ideal, as it would not allow for the observation of the segregation of the two genes being tested.

Question 17

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

Accepted Answer

Chi-square analysis is a statistical method used to determine if there is a significant difference between observed and expected values. In genetics, it is commonly used to determine whether the observed data support the hypothesis of genetic linkage or not. By comparing the observed data with the expected values, chi-square analysis can determine if the difference between the two is statistically significant, indicating the presence of genetic linkage. The other options listed are all types of test crosses, which are used to determine the genotypes or inheritance patterns of individuals, but do not specifically test for genetic linkage. Recombination frequency (r) calculation is a measure of genetic distances between genes, but it alone does not provide evidence of genetic linkage.

Question 18

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.

Accepted Answer

The answer of Which type of crossover event produces two...

Question 19

If you are given a recombination frequency of 34% between genes X and Y and 27% between X and Z,can you predict the order of the three genes?
A)Yes;the order is X-Z-Y.
B)Yes;the order is X-Y-Z.
C)Yes;the order is Z-X-Y.
D)No;based on this data alone,the order could be Z-Y-X or X-Y-Z.
E)No;based on this data alone,the order could be X-Z-Y or Z-X-Y.

Accepted Answer

Based on the recombination frequencies, it is clear that X is in the middle, as it has a lower recombination frequency with both Y and Z than the recombination frequency between Y and Z. However, we cannot determine if Z or Y is the gene that is farthest away from X. Therefore, the order could be X-Z-Y or Z-X-Y.

Question 20

Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes.How many genotypes are produced in a four-gene cross with incomplete genetic linkage?
A)4
B)8
C)16
D)20
E)24

Accepted Answer

In a trihybrid cross, the possible gamete genotypes are 2³ = 8 due to incomplete genetic linkage of three genes. In a four-gene cross, the possible gamete genotypes would be 2⁴ = 16 due to the independent assortment of the four genes during meiosis. Therefore, the answer is C)16.

Quiz 5: Genetic Linkage and Mapping in Eukaryotes

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) ?

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

When does recombination occur?

Which type of crossover event produces no recombinant chromosomes?

Genetic linkage leads to the production of a significantly greater than expected number of gametes containing chromosomes with

Intragenic recombination can be detected

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?

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

Syntenic genes can assort independently when

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) ?

Where does crossing over occur?

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?

The Huntington disease (HD) allele was discovered

The alleles of linked genes tend to

Which type of crossover event produces all four recombinant chromosomes?

In a two-point test-cross analysis,a dihybrid F₁ fly is crossed to a

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?

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

If you are given a recombination frequency of 34% between genes X and Y and 27% between X and Z,can you predict the order of the three genes?

Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes.How many genotypes are produced in a four-gene cross with incomplete genetic linkage?