Deck 5: Chromosome Mapping in Eukaryotes

Question 1

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

Answer 1

E

Question 2

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?

Answer 2

48

Question 3

Who was the student in Morgan's laboratory who first realized that the sequence of genes could be determined by Morgan's proposal that two genes located relatively close to each other are less likely to form chiasma between them than if the two genes were relatively far apart?

Answer 3

A.H.Sturtevant

Question 4

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 the following circumstance:

A) sex-linked inheritance with 30% crossing over.
B) linkage with 50% crossing over.
C) linkage with approximately 33 map units between the two gene loci.
D) independent assortment.
E) 100% recombination.

Question 5

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

A) the genome sequence of a species
B) the inclusion of the X and Y chromosome in SNP experiments
C) the use of synteny
D) positive interference
E) negative interference

Question 6

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 phenotypes,and in what numbers would they be expected?

Question 7

What two terms apply to the fusion of cultured human and mouse cells that produces cell lines that are useful in assigning a gene to a particular human chromosome?

A) forward and reverse
B) lod score and pod score
C) heterokaryon and synkaryon
D) single and double
E) positive and negative

Question 8

Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb,Aabb,aaBb,aabb.These results are consistent with the following circumstance:

A) independent assortment.
B) alternation of generations.
C) complete linkage.
D) incomplete dominance.
E) hemizygosity.

Question 9

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,and the following phenotypes were observed:
smooth abdomen,straw body 820
Lobe 780
smooth abdomen,Lobe 42
straw body 58
smooth abdomen 148
Lobe,straw body 152
a) Give the gene order and map units between these three loci.
b) What is the coefficient of coincidence?

Question 10

Assume that a cross is made between AaBb and aabb plants and that all the offspring are either AaBb or aabb.These results are consistent with the following circumstance:

A) complete linkage.
B) alternation of generations.
C) codominance.
D) incomplete dominance.
E) hemizygosity.

Question 11

Phenotypically wild-type F₁ female Drosophila,whose mothers had light eyes (lt)and fathers had straw (stw)bristles,produced the following offspring when crossed to homozygous light-straw males:
Compute the map distance between the light and straw loci.

Question 12

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

A) chiasma.
B) negative interference.
C) reciprocal genetic exchange.
D) positive interference.
E) mitotic recombination.

Question 13

What is the relationship between the degree of crossing over and the distance between two genes?

Question 14

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

A) discontinuous inheritance
B) Mendelian inheritance
C) linkage
D) tetrad analysis
E) dominance and/or recessiveness

Question 15

Diagram chromosomal events that will ultimately result in the segregation of alleles (A and a)during meiosis II rather than meiosis I.

Question 16

The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila.Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany,ebony males.Of 1000 offspring,what would be the expected phenotypes,and in what numbers would they be expected?

Question 17

Under what circumstance might two loci be on the same chromosome but behave as if independently assorting in crosses?

Question 18

Methods for determining the linkage group and genetic map in humans involve which of the following?

A) DNA markers
B) twin spots and tetrad analysis
C) tetrad analysis and bromodeoxyuridine
D) zygotene and pachytene DNA synthesis
E) chiasmatype and classical analyses

Question 19

At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?

Question 20

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 phenotypes and frequencies expected.

Question 21

Assume that two genes are 80 map units apart on chromosome II of Drosophila and that a cross is made between a doubly heterozygous female and a homozygous recessive male.What percent recombination would be expected in the offspring of this type of cross?

Question 22

(a)In a three-point mapping experiment,what three general classes of offspring are expected (assuming crossovers occur)? (b)How many different genotypic classes are expected?

Question 23

What are two commonly used DNA landmarks for mapping human genes?

Question 24

Describe a convenient method for determining gene order from three-point cross results.

Question 25

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 there are 20 map units between the G and E loci.

Question 26

If two gene loci are on nonhomologous chromosomes,genes at these loci are expected to assort independently.

Question 27

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

Question 28

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 the G and E loci assort independently.

Question 29

Linkage (viewed from results of typical crosses)always occurs when two loci are on the same chromosome.

Question 30

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 what arrangement of genes?

Question 31

In the fruit fly,Drosophila melanogaster,a spineless (no wing bristles)female fly is mated to a male that is claret (dark eyes)and hairless (no thoracic bristles).Phenotypically wild-type F₁ female progeny were mated to fully homozygous (mutant)males,and the following progeny (1000 total)were observed:
a) Which gene is in the middle?
b) With respect to the three genes mentioned in the problem,what are the genotypes of the homozygous parents used in making the phenotypically wild-type F₁ heterozygote?
c) What are the map distances between the three genes? A correct formula with the values "plugged in" for each distance will be sufficient.
d) What is the coefficient of coincidence? A correct formula with the values "plugged in" will be sufficient.

Question 32

Three loci,mitochondrial malate dehydrogenase that forms a and b (MDHa,MDHb),glucuronidase that forms 1 and 2 (GUS1,GUS2),and a histone gene that forms + and -
(H⁺,ᴴ-),are located on chromosome #7 in humans.Assume that the MDH locus is at position 35,GUS at position 45,and H at position 75.A female whose mother was homozygous for MDHa,GUS2,and H⁺ and whose father was homozygous for MDHb,GUS1,and H- produces a sample of 1000 egg cells.Give the genotypes and expected numbers of the various types of cells she would produce.Assume no chromosomal interference.

Question 33

Provide a brief definition for positive interference.

Question 34

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?

Question 35

Two lines of work indicated that crossing over actually involves breakage and reunion of chromatid material.What organisms were involved,and who did the work?

Question 36

Positive interference occurs when a crossover in one region of a chromosome reduces crossovers in nearby regions.

Question 37

Given that loci A and B in Drosophila are sex-linked and 20 map units apart,what phenotypic frequencies would you expect in male and female offspring resulting from the following crosses? (Assume that A and B are dominant to a and b,respectively.)
a) AaBb (dominant alleles on same chromosome)female × ab/Y male
b) AaBb (dominant alleles on homologs)female × ab/Y male
c) aabb female × AB/Y male (no crossing over in male Drosophila)

Question 38

What advantage does BrdU (bromodeoxyuridine)have in the study of chromosome structure and recombination?

Question 39

Sister chromatid exchanges increase in frequency in the presence of X-rays,certain viruses,ultraviolet light,and certain chemical mutagens.In what autosomal recessive disorder is there known to be an increase in sister chromatid exchanges?

Question 40

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 the recombinant progeny are gE/ge and Ge/ge.

Question 41

Restriction fragment length polymorphisms (RFLPs),microsatellites,and single-nucleotide polymorphisms (SNPs)were used by Morgan and Sturtevant to discover linkage in Drosophila.

Question 42

Exchanges occur between homologous chromosomes,but never between sister chromatids.

Question 43

Mendel predicted that some genes will be carried in the same chromosome.