Question 1

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?

Accepted Answer

48

Question 2

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

Accepted Answer

If the genes are far apart, they may show independent assortment.

Question 3

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

Accepted Answer

The results are consistent with complete linkage because the offspring only show the parental genotypes (AaBb or aabb) without any recombination, indicating that the genes are linked and inherited together.

Question 4

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.

Accepted Answer

The answer of In Drosophila, assume that the gene for...

Question 5

What is the expected evolutionary significance of genetic recombination?

Accepted Answer

The answer of What is the expected evolutionary significance of...

Question 6

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 for 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.

Accepted Answer

The answer of In the fruit fly, Drosophila melanogaster, a...

Question 7

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

Accepted Answer

The answer of At what stage of the meiotic cell...

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

Accepted Answer

The offspring showing approximately equal numbers of each genotype suggests that the genes are assorting independently, consistent with Mendel's law of independent assortment.

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:
  a() Give the gene order and map units for these three loci.
b() What is the coefficient of coincidence?

Accepted Answer

The answer of Assume that investigators crossed a strain of...

Question 10

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

Accepted Answer

The observed offspring ratios suggest linkage with approximately 33 map units between the two gene loci, as the recombinant types (Aabb and aaBb) are less frequent than the parental types (AaBb and aabb), indicating partial linkage rather than independent assortment.

Question 11

When two genes fail to assort independently, the term normally applied is
A) discontinuous inheritance
B) Mendelian inheritance
C) linkage
D) dominance and/or recessiveness
E) tetrad analysis

Accepted Answer

Linkage refers to the phenomenon where two genes are located close to each other on the same chromosome and tend to be inherited together, thus failing to assort independently.

Question 12

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?

Accepted Answer

The answer of The genes for mahogany eyes and ebony...

Question 13

The phenomenon in which one crossover decreases the likelihood of crossovers in nearby regions is called _.
A) chiasma
B) reciprocal genetic exchange
C) positive interference
D) negative interference
E) mitotic recombination

Accepted Answer

Positive interference is the phenomenon where one crossover event reduces the probability of another crossover occurring nearby.

Question 14

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

Accepted Answer

The answer of Diagram chromosomal events that will ultimately result...

Question 15

In the early 1900s, two scientists noted there were many more genes than chromosome pairs, thus setting the stage for the suggestion that some gene loci might be linked
during meiotic processes. Who were these two scientists?

Accepted Answer

The answer of In the early 1900s, two scientists noted...

Question 16

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.

Accepted Answer

The answer of Phenotypically wild -type F1 female Drosophila, whose...

Question 17

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?

Accepted Answer

The answer of Assume that the genes for tan body...

Question 18

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

Accepted Answer

The answer of What is the relationship between the degree...

Question 19

Methods for determining the linkage group and genetic map in humans involve _.
A) DNA markers
B) zygotene and pachytene DNA synthesis
C) tetrad analysis and bromodeoxyuridine
D) twin spots and tetrad analysis
E) chiasmatype and classical analyses

Accepted Answer

DNA markers are used in humans to determine linkage groups and create genetic maps by identifying the location of genes on chromosomes through linkage analysis.

Question 20

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 which arrangement of alleles?

Accepted Answer

The answer of Assume that a cross is made between...

Quiz 7: Linkage and Chromosome Mapping in Eukaryotes

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?

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

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 _.

What is the expected evolutionary significance of genetic recombination?

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

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 _.

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 ________.

When two genes fail to assort independently, the term normally applied is

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

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

In the early 1900s, two scientists noted there were many more genes than chromosome pairs, thus setting the stage for the suggestion that some gene loci might be linked during meiotic processes. Who were these two scientists?

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.

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

Methods for determining the linkage group and genetic map in humans involve _.

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 which arrangement of alleles?