Deck 7: Chromosomal Basis of Inheritance

Question 1

Visible tetrads are produced during the reproductive cycle of

A) Saccharomyces cerevisiae
B) Neurospora crassa
C) Chlamydomonas reinhardtii
D) Zea mays
E) all but D.

Answer 1

E

Question 2

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

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

Answer 2

D

Question 3

In tumor cells of humans with hereditary retinoblasta

A) the gene RB is mutant at both loci.
B) the gene RB is mutant at one locus.
C) there is a duplication of the RB locus.
D) there is a 10 percent recombination rate.
E) the RB locus is missing.

Answer 3

A

Question 4

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

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 5

The order of the four spore pairs within an ascus of an ordered tetrad reflects

A) the orientation of the four chromatids of each tetrad at the metaphase plate of meiosis I.
B) whether or not mitosis takes place after meiosis.
C) the number of recombination events.
D) both A and B.
E) all of the above.

Question 6

One map unit on a human chromosome corresponds roughly to

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

Question 7

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

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 8

A tetratype tetrad resulting from a two-point cross between a wild-type Neurospora cell and a double mutant call will contain ascospores with

A) both the parental and recombinant genotypes.
B) one parental and one recombinant genotype.
C) both parental genotypes.
D) only the recombinant genotype.
E) only the dominant parental genotypes.

Question 9

Mitotic recombination cannot occur in cells that are

A) haploid.
B) aneuploid.
C) diploid.
D) polyploid.
E) all of the above.

Question 10

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

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 11

The fusion of the nuclei of a heterokaryon is called

A) diploidization.
B) spore production.
C) recombination.
D) haploidization.
E) syngamy.

Question 12

Tetrad analysis to create genetic maps is best performed with haploid organisms because

A) only the dominant alleles are expressed.
B) only recessive alleles are expressed.
C) only haploid organisms produce spores.
D) the phenotype directly reflects the genotype.
E) haploid organisms have two copies of each gene.

Question 13

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

Question 14

If a single crossover occurs during mitosis in heterozygotes, then

A) loci distal to the crossover on the same chromosome arm may become homozygous.
B) recessive phenotypes can be expressed.
C) phenotypic changes are not observed.
D) only wild-type phenotypes are observed.
E) Both A and B

Question 15

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

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

Question 16

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

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 17

During sexual reproduction in Neurospora crassa, fusion of the haploid nuclei of cells with different mating types results in ________ ascospores in an ascus.

A) eight haploid
B) eight diploid
C) four diploid and four haploid
D) four diploid
E) four haploid

Question 18

When do you observe the 4:4 segregation pattern of genes in a linear tetrad?

A) When the gene-centromere distance is greater than 7 map units
B) When the parent is a homozygote
C) When a single crossover between a gene and its centromere occurs
D) When no crossover between a gene and its centromere occurs
E) When the parent is a heterozygote

Question 19

Organisms that achieve genetic recombination without undergoing the normal processes of meiosis and fertilization are said to have

A) alternation of generations.
B) asexual systems.
C) sporadic sexual systems.
D) parasexual systems.
E) unisexual systems

Question 20

First-division segregation means that

A) both copies of an allelic pair are at the same pole after meiosis I.
B) centromeres of homologs segregate to different nuclear areas after the first meiotic division.
C) no crossover has occurred between a gene locus and the centromere.
D) Both A and B
E) All of the above

Question 21

A diploid culture of Aspergillus with the genotype w ad+ pro paba+ y+ bi/w ad pro+ paba y bi+ undergoes haploidization in some sectors. The resulting haploid genotypes and their proportions are 50 percent w ad+ pro paba+ y+ bi, and 50 percent w ad pro+ paba y bi+. How do you explain these results?

Question 22

How many different types of tetrads can result from a two-point cross between a wild-type Neurospora cell and a double-mutant cell?

Question 23

What are the possible segregation patterns and genotype ratios of genes C and c in a linear tetrad in the case of second-division segregation?

Question 24

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?

Question 25

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.

Question 26

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

Question 27

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

Question 28

Mitotic recombination occurs less frequently than meiotic recombination.

Question 29

How can mitotic crossing over be used to map gene order on heterozygous chromosomes?

Question 30

In an ordered tetrad, if segregation of alleles occurs during meiosis II, a crossover event has occurred between the alleles and the chromosomal centromere.

Question 31

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

Question 32

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

Question 33

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?

Question 34

In order for mitotic crossover to occur, chromosomes line up at random at the metaphase plate.

Question 35

At what stage may mitotic recombination occur?

Question 36

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

Question 37

Vegetative cells in the alga Chlamydomonas reinhardtii are diploid.

Question 38

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

Question 39

What are heterokaryons?

Question 40

Why do Neurospora crassa asci contain eight rather than four haploid spores?

Question 41

A woman marries a man with two rare, recessive X-linked alleles, a and b. Their daughter marries a normal a+ b+/Y man. What will the phenotypes of their female children be?

Question 42

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

Question 43

What is FISH used for and how does it work?