Question 1

How can you calculate the recombination frequency between a and b in the previous question?

Accepted Answer

We can assume that the grandmother is homozygous wild-type for the genes, since the recessive alleles are rare. Her daughter will then be a heterozygote (a+ b+/a b). When she marries a normal a+ b+/Y man, their male children will express all four possible phenotypic classes (since they are hemizygous): the female parental a+ b+ and ab and the recombinants a+ b and a b+. If a large number of such pedigrees are available, the recombination frequency can be calculated.

Question 2

How does the arrangement of ascospores in the tetrads of yeast differ from that in Neurospora crassa?

Accepted Answer

The ascospores in a tetrad of yeast are unordered (random), whereas those of Neurospora are linearly ordered.

Question 3

Explain how the two formulas for determining the distance between linked genes in diploid organisms and in tetrad analysis relate to each other.

Accepted Answer

In diploid organisms, we calculate the recombination frequency by determining the percentage of recombinant progeny out of the total number of progeny. In tetrad analysis, we determine the proportion of recombinant spores in tetrads produced from crosses out of the total number of spores. Therefore, in diploid organisms, the formula is: (number of recombinants/total number of progeny) × 100. In tetrad analysis, it is: (1/2T + NPD/total tetrads) × 100.

Question 4

Neurospora crassa, a mycelial-form fungus, is useful for genetic and biochemical studies because it

Accepted Answer

A)  produces meiotic products contained in an ascus. 
B)  is haploid. 
C)  has a relatively short life cycle. 
D)  All of the above 
E)  None of the above 
A)  produces meiotic products contained in an ascus. 
B)  is haploid. 
C)  has a relatively short life cycle. 
D)  All of the above 
E)  None of the above

Question 5

During the analysis of an ordered tetrad, 22 percent of the asci showed second-division segregation for a particular genetic locus. What is the distance between the gene and the centromere?

Accepted Answer

Eleven map

Question 6

X-linked genes in humans are easier to study than autosomal genes because

Accepted Answer

A)  recombination frequencies are lower. 
B)  hemizygosity in males allows the effects of genotypic pairings to be observed. 
C)  Suitable pedigrees are easily available. 
D)  they do not have as high a recombination rate. 
E)  there are fewer genes to deal with. 
A)  recombination frequencies are lower. 
B)  hemizygosity in males allows the effects of genotypic pairings to be observed. 
C)  Suitable pedigrees are easily available. 
D)  they do not have as high a recombination rate. 
E)  there are fewer genes to deal with.

Question 7

DNA markers allow genetic mapping in humans on the basis of molecular phenotypes, rather than outwardly visible phenotypes.

Accepted Answer

A) True 
 B)False

Question 8

Describe the possible tetrad types resulting from a cross qr × q+r+ in which the genes are located on separate chromosomes.

Accepted Answer

Depending on the metaphase alignment of

Question 9

A polymorphic DNA marker is one in which more than one type of sequence is found in the population at that site in the genome.

Accepted Answer

A) True 
 B)False

Question 10

Mitotic rather than meiotic recombination analysis has been used to construct genetic maps in the fungus Aspergillus.

Accepted Answer

A) True 
 B)False

Question 11

Following a series of two-point testcrosses in Neurospora, 200 tetrads were analyzed. Of these, 100 were PD and 100 were NPD. These two genes are

Accepted Answer

A)  50 map units apart on the same chromosome. 
B)  100 map units apart on the same chromosome. 
C)  epistatic. 
D)  on different chromosomes. 
E)  adjacent to each other on the same chromosome. 
A)  50 map units apart on the same chromosome. 
B)  100 map units apart on the same chromosome. 
C)  epistatic. 
D)  on different chromosomes. 
E)  adjacent to each other on the same chromosome.

Question 12

If two genes are linked, then the frequency of parental ditype tetrads resulting from a two-point testcross will be

Accepted Answer

A)  equal to the frequency of nonparental ditype tetrads. 
B)  equal to the frequency of the tetratype tetrads. 
C)  greater than the frequency of the nonparental ditype tetrads. 
D)  less than the frequency of tetratype tetrads. 
E)  none of the above. 
A)  equal to the frequency of nonparental ditype tetrads. 
B)  equal to the frequency of the tetratype tetrads. 
C)  greater than the frequency of the nonparental ditype tetrads. 
D)  less than the frequency of tetratype tetrads. 
E)  none of the above.

Question 13

In order to use tetrad analysis in an organism to map the distance between a gene and the centromere on a chromosome,

Accepted Answer

A)  the organism may produce either ordered or unordered tetrads. 
B)  the organism must produce unordered tetrads. 
C)  the parental centromeres must be distinguishable. 
D)  the chromosome must have a cytological marker. 
E)  the organism must produce ordered tetrads. 
A)  the organism may produce either ordered or unordered tetrads. 
B)  the organism must produce unordered tetrads. 
C)  the parental centromeres must be distinguishable. 
D)  the chromosome must have a cytological marker. 
E)  the organism must produce ordered tetrads.

Question 14

What process observed by Curt Stern resulted in twin spot formation in Drosophila?

Accepted Answer

A)  Chromosome loss 
B)  Mitotic recombination 
C)  Chromosome nondisjunction 
D)  Meiotic recombination 
E)  Incomplete dominance 
A)  Chromosome loss 
B)  Mitotic recombination 
C)  Chromosome nondisjunction 
D)  Meiotic recombination 
E)  Incomplete dominance

Question 15

In the life cycles of yeast and Chlamydomonas, the haploid vegetative cells never undergo fusion to form a diploid cell.

Accepted Answer

A) True 
 B)False

Question 16

One map unit on a human chromosome corresponds roughly to

Accepted Answer

A)  10 base pairs. 
B)  1 million base pairs. 
C)  1 base pair. 
D)  100,000 base pairs. 
E)  1,000 base pairs. 
A)  10 base pairs. 
B)  1 million base pairs. 
C)  1 base pair. 
D)  100,000 base pairs. 
E)  1,000 base pairs.

Question 17

At what stage may mitotic recombination occur?

Accepted Answer

When homologs align

Question 18

If 156 tetrads are analyzed following a series of two-point testcrosses in Neurospora, and 102 of them are PD, 40 are T, and the remaining 14 are NPD, what is the frequency of recombination between the two genes?

Accepted Answer

The recombination frequency is

Question 19

What are heterokaryons?

Accepted Answer

They are fungal cells in which

Question 20

In the yeast Saccharomyces cerevisiae, when an MATa mating type fuses with a MATα mating type, the resulting cell is diploid.

Accepted Answer

A) True 
 B)False

Exam 7: Chromosomal Basis of Inheritance

How can you calculate the recombination frequency between a and b in the previous question?

How does the arrangement of ascospores in the tetrads of yeast differ from that in Neurospora crassa?

Explain how the two formulas for determining the distance between linked genes in diploid organisms and in tetrad analysis relate to each other.

Neurospora crassa, a mycelial-form fungus, is useful for genetic and biochemical studies because it

During the analysis of an ordered tetrad, 22 percent of the asci showed second-division segregation for a particular genetic locus. What is the distance between the gene and the centromere?

X-linked genes in humans are easier to study than autosomal genes because

DNA markers allow genetic mapping in humans on the basis of molecular phenotypes, rather than outwardly visible phenotypes.

Describe the possible tetrad types resulting from a cross qr × q+r+ in which the genes are located on separate chromosomes.

A polymorphic DNA marker is one in which more than one type of sequence is found in the population at that site in the genome.

Mitotic rather than meiotic recombination analysis has been used to construct genetic maps in the fungus Aspergillus.

Following a series of two-point testcrosses in Neurospora, 200 tetrads were analyzed. Of these, 100 were PD and 100 were NPD. These two genes are

If two genes are linked, then the frequency of parental ditype tetrads resulting from a two-point testcross will be

In order to use tetrad analysis in an organism to map the distance between a gene and the centromere on a chromosome,

What process observed by Curt Stern resulted in twin spot formation in Drosophila?

In the life cycles of yeast and Chlamydomonas, the haploid vegetative cells never undergo fusion to form a diploid cell.

One map unit on a human chromosome corresponds roughly to

At what stage may mitotic recombination occur?

If 156 tetrads are analyzed following a series of two-point testcrosses in Neurospora, and 102 of them are PD, 40 are T, and the remaining 14 are NPD, what is the frequency of recombination between the two genes?

What are heterokaryons?

In the yeast Saccharomyces cerevisiae, when an MATa mating type fuses with a MATα mating type, the resulting cell is diploid.

Genetics of Bacteria and Bacteriophages

Variations in Chromosome Structure and Number

Advanced Gene Mapping in Eukaryotes

Gene Mapping in Eukaryotes

Quantitative Genetics

Extensions of Mendelian Genetic Principles

Molecular Evolution

Population Genetics

Non-Mendelian Inheritance

Genetics of Cancer

Genetic Analysis of Development

Regulation of Gene Expression in Eukaryotes

Mendelian Genetics

Regulation of Gene Expression in Bacteria and Bacteriophages

Genomics

Applications of Recombinant DNA Technology

Recombinant DNA Technology

DNA Mutation, DNA Repair, and Transposable Elements

Gene Expression: Translation

Gene Expression: Transcription

Gene Control of Proteins

DNA Replication

DNA: The Genetic Material

Genetics: an Introduction

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