Question 1

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.

Accepted Answer

Complete linkage explains the observed offspring types because it suggests that the A and B alleles are inherited together due to their close proximity on the chromosome, preventing the assortment of different allele combinations.

Question 2

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 3

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

mahogany = 375; ebony = 375; wild-type = 125; mahogany-ebony = 125.

Question 4

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?

Accepted Answer

The answer of Who was the student in Morgan's laboratory...

Question 5

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.

Accepted Answer

Positive interference refers to the phenomenon where the occurrence of a crossover event in a particular region of a chromosome decreases the probability of another crossover happening nearby. This ensures a more even distribution of genetic material during meiosis.

Question 6

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

Accepted Answer

A chromosome with a unique cytological marker allowed Creighton and McClintock to track the physical exchange between chromatids during crossing over. This marker allowed them to distinguish between the two chromosomes involved in the exchange, as well as track the inheritance of the exchanged segment in subsequent generations.

Question 7

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

Accepted Answer

The answer of Under what circumstance might two loci be...

Question 8

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 9

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?

Accepted Answer

The answer of Assume that there are 12 map units...

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 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.

Accepted Answer

The results of the cross suggest that the two genes are linked but with a distance of approximately 33 map units between them. This is indicated by the higher number of parental (AaBb and aabb) offspring compared to recombinant (Aabb and aaBb) offspring. The percentage of recombinants is approximately equal to the distance between the genes in map units. Therefore, the correct answer is C. Sex-linked inheritance, linkage with 50% crossing over, independent assortment, and 100% recombination would all result in different offspring ratios.

Question 11

Phenotypically wild-type F₁female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males:

Phenotype	Number
light-straw	22
wild-type	18
light	990
straw	970
total	2000

Compute the map distance between the light and straw loci.

Accepted Answer

The answer of Phenotypically wild-type F₁female Drosophila, whose mothers...

Question 12

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

Accepted Answer

DNA markers are commonly used in determining the linkage group and genetic map in humans. Techniques such as restriction fragment length polymorphism (RFLP) analysis, variable number tandem repeat (VNTR) analysis, and microsatellite analysis can all be used to identify DNA markers that are located near genes of interest and can be used to create a genetic map. Twin spots, tetrad analysis, bromodeoxyuridine, zygotene and pachytene DNA synthesis, and chiasmatype and classical analyses are all techniques used in other areas of genetics research and are not directly related to determining the linkage group and genetic map in humans.

Question 13

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 14

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 15

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.

Accepted Answer

The equal distribution of phenotypes indicates that the alleles for A and B assort independently of each other during meiosis. This is consistent with Mendelian genetics and the principle of independent assortment.

Question 16

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

Accepted Answer

The term applied when two genes fail to assort independently is called linkage. Linkage occurs when two genes are located close together on a chromosome and tend to be inherited together. This violates Mendel's law of independent assortment, which states that genes on different chromosomes are inherited independently of each other. Discontinuous inheritance, Mendelian inheritance, dominance and/or recessiveness, and tetrad analysis are not the appropriate terms for this concept.

Question 17

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

Accepted Answer

The terms heterokaryon and synkaryon apply to the fusion of cultured human and mouse cells. Heterokaryon refers to a cell containing two or more nuclei from different cells, while synkaryon refers to a cell containing two or more nuclei that have merged into a single nucleus. The fusion of human and mouse cells creates heterokaryons, which eventually become synkaryons through nuclear fusion. These hybrid cell lines are useful in assigning a gene to a particular human chromosome through techniques such as cell sorting and genetic mapping.

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

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?

Accepted Answer

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

Question 20

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

Accepted Answer

The genome sequence of a species allows for more precise identification and tracking of genetic markers, making classical genetic mapping approaches less relevant.

Quiz 5: Chromosome Mapping in Eukaryotes

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:

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

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?

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

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?

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

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

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?

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:

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

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:

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

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?

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

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