Question 1

Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome?
A)the genes are very far apart on the same chromosome,such that there is always a crossover between them
B)the genes are very close together on the chromosome,such that there is never a crossover between them
C)too large a sample size
D)the genes are very far apart on the same chromosome,such that there is never a crossover between them
E)a mating between consanguineous individuals

Accepted Answer

When genes are very far apart on the same chromosome, the likelihood of a crossover event occurring between them in every meiosis is high. This can mimic independent assortment, which is observed when genes are on different chromosomes, leading to the erroneous conclusion that the genes are not linked when they are actually on the same chromosome.

Question 2

The genes for purple eyes and curved wings are approximately 21 map units apart on chromosome II in Drosophila.Assume that a purple-eyed female was mated to a curved wing male and that the resulting F₁ phenotypically wild-type females were mated to purple,curved males.Of 1000 offspring,what would be the expected number of flies with purple eyes and curved wings? A)540 B)395 C)210 D)790 E)105

Accepted Answer

B

Question 3

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 . A)the G and E loci are segregating independently B)the G and E loci are linked C)the G and E loci reside on the same chromosome over 50 map units apart D)the G and E loci show complete linkage E)the G and E loci assort independently

Accepted Answer

The progeny distribution suggests linkage between the G and E loci because the parental phenotypes (GE/ge and ge/ge) are more common than the recombinant phenotypes (gE/ge and Ge/ge), indicating that the G and E genes are linked and do not assort independently.

Question 4

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______ . A)the recombinant progeny are Ge/Ge and gE/gE B)the recombinant progeny are gE/ge and Ge/ge C)the recombinant progeny are GE/GE and ge/ge D)the recombinant progeny are gE/GE and GE/ge E)the recombinant progeny are GE/ge and GE/ge

Accepted Answer

The two parental genotypes are GE/ge and ge/ge, and the resulting progeny genotypes are GE/ge, gE/ge, Ge/ge, and ge/ge. The recombinant progeny are those that have a different combination of alleles than the parental genotypes. In this case, gE/ge and Ge/ge are the recombinant genotypes because they have a different allele combination than the two parental genotypes. Therefore, option B is the correct choice.

Question 5

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: Compute the map distance between the light and straw loci. A)4 map units B)98 map units C)12 map units D)8 map units E)2 map units

Accepted Answer

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

Question 6

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?
A)Charles Darwin
B)Barbara McClintock
C)Thomas Hunt
D)A)H.Sturtevant
E)Gregor Mendel

Accepted Answer

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 was H. Sturtevant.

Question 7

At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?
A)during synapsis in prometaphase
B)at the four-strand stage of meiosis,after synapsis of homologous chromosomes,and before the end of prophase I
C)in S phase of meiosis
D)during synapsis at the four-strand stage of meiosis
E)during bivalent formation,after synapsis of homologous chromosomes,and before the end of prophase I

Accepted Answer

Crossing over occurs at the four-strand stage of meiosis, after synapsis of homologous chromosomes and before the end of prophase I. This is when homologous chromosomes exchange genetic material.

Question 8

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 F₁Lobe females were then backcrossed with homozygous smooth abdomen,straw body males,the following phenotypes were observed: A)smooth,Lobe,straw B)it is impossible to tell C)Lobe,smooth,straw D)smooth,straw,Lobe E)Lobe,straw,smooth

Accepted Answer

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

Question 9

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 map units between the G and E loci. A)15 B)25 C)10 D)5 E)20

Accepted Answer

The answer of The cross GE/ge × ge/ge produces the...

Question 10

Choose the true statement below.
A)When two genes are over 50 map units apart,a crossover can theoretically occur 100% of the time.
B)The percentage of tetrads involved in exchange between two genes is equal to the number of recombinant progeny seen.
C)Linkage viewed from results of typical crosses always occurs when two loci are on the same chromosome.
D)When two genes are over 50 map units apart,a crossover would theoretically occur 0% of the time.
E)A single crossover on a chromosome will always yield the recombinant phenotype of the genes you are interested in.

Accepted Answer

When two genes are over 50 map units apart, they behave as if they are independently assorting because the likelihood of a crossover event occurring between them is so high, theoretically up to 100%. This is because the distance allows for multiple crossover events to potentially occur, making their segregation appear as if they are on separate chromosomes.

Question 11

Which of the following statements is true?
A)The linkage ratio is best seen in genes on nonhomologous chromosomes.
B)If two gene loci are on nonhomologous chromosomes,genes at these loci are expected to assort independently.
C)Linkage without crossing over leads to all recombinant chromosomes.
D)The chromosomal theory of inheritance denotes that linked alleles will never be separated.
E)A centromere and its surrounding genes constitute a linkage group.

Accepted Answer

If two gene loci are on nonhomologous chromosomes, they are on different chromosomes that do not pair during meiosis. Therefore, alleles at these loci are expected to assort independently. This is known as independent assortment.

Question 12

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

Accepted Answer

The results suggest linkage with approximately 33 map units between the two gene loci because the parental phenotypes (AaBb and aabb) are more common than the recombinant phenotypes (Aabb and aaBb), indicating that the genes are linked but recombination has occurred, with the recombinant phenotypes (100 total) making up about 33% of the offspring (300 total), suggesting a recombination frequency of approximately 33%.

Question 13

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 of wild-type offspring,and in what numbers would they be expected? A)75 B)425 C)50 D)350 E)8

Accepted Answer

The cross can be represented as: 
X^B/X^B T/T x X^+/Y T/T
where X represents the wild-type allele for body color and T represents the wild-type allele for wing shape. 
From the first cross, we know that the female is X^B/X^+ T/T and the male is X^+/Y T/T. Their F1 offspring will all be X^B/X^+ T/T, since they inherit one X chromosome from each parent and both parents are heterozygous for body color and homozygous for wing shape. 
The F1 offspring are then crossed to tan-bodied, bare-winged males, who must be X^B/Y T/T. The expected offspring from this cross can be calculated using a dihybrid cross with a recombination frequency of 15 map units:
X^B/T x X^+/T -> X^B/T ; X^+/T ; X^B/T ; X^+/T (recombinants)
X^B/T x Y/T -> X^B/T ; Y/T (non-recombinants)
X^+/T x Y/T -> X^+/T ; Y/T (non-recombinants)
Expected ratios:
X^B/T ; X^+/T ; X^B/T ; X^+/T (recombinants) = 2(1/2)(1/2)(1/2)(1/2) x 1000 = 250
X^B/T ; Y/T (non-recombinants) = 1/2(1/2)(1/2)(1/2) x 1000 = 62.5
X^+/T ; Y/T (non-recombinants) = 1/2(1/2)(1/2)(1/2) x 1000 = 62.5
Total wild-type offspring: 250 + 62.5 + 62.5 = 375
Therefore, the answer is B) 425.

Question 14

What term is applied when two genes fail to assort independently,that is,they tend to segregate together during gamete formation?
A)tetrad analysis
B)Mendelian inheritance
C)discontinuous inheritance
D)dominance and/or recessiveness
E)linkage

Accepted Answer

The term for when two genes fail to assort independently is called linkage. This means that the genes are located close together on the same chromosome, causing them to be inherited together more often than not during gamete formation. This can affect the expected ratios of offspring genotype frequencies in a cross, and can be used to map the location of genes on chromosomes.

Question 15

Below is a diagram during crossing over.Describe the outcome. 
A)offspring will not look like either parent
B)a 1:1 ratio
C)formation of parental alleles only
D)segregation of alleles A and a during meiosis II
E)segregation of alleles A and a during meiosis I

Accepted Answer

The answer of Below is a diagram during crossing over.Describe...

Question 16

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?
A)96
B)48
C)6
D)12
E)24

Accepted Answer

The frequency of chiasma formation between two loci is proportional to the distance between them. In this case, the distance is 12 map units. Therefore, the probability of a chiasma forming between the two loci is 12/100 or 0.12 (assuming one chiasma per meiosis).

For each oocyte, there is a 0.12 probability of a chiasma forming between the two loci. The probability of no chiasma forming is 0.88. Thus, the number of oocytes expected to have a chiasma between the two loci is:

200 x 0.12 = 24

However, since there are two homologous chromosomes, there are two chances for a chiasma to form between the two loci. Therefore, we must double the expected number of oocytes with a chiasma between the two loci:

24 x 2 = 48

Question 17

What is the relationship between the degree of crossing over and the distance between two genes?
A)There is no correlation.
B)It is direct: as the distance decreases,the frequency of recombination increases.
C)It is indirect: as the distance decreases,the frequency of recombination doubles.
D)It is indirect: as the distance increases,the frequency of recombination doubles.
E)It is direct: as the distance increases,the frequency of recombination increases.

Accepted Answer

The relationship between the degree of crossing over and the distance between two genes is direct, meaning that as the distance between two genes increases, the frequency of recombination also increases. This is due to the fact that the further apart two genes are located on a chromosome, the greater the chance that multiple crossovers will occur during meiosis, which can result in an increased frequency of recombinant gametes. Therefore, Choice E is the best choice.

Question 18

If complete linkage occurs,we expect ______. A)to see all four types of offspring B)a 1:1:1:1 ratio in the test cross C)to see only parental phenotypes in the F₂of the appropriate test cross D)to see only recombinant phenotypes in the F₂of the appropriate test cross E)a 9:3:3:1 ratio in the F₂

Accepted Answer

Complete linkage means that the two loci are so close together on the chromosome that no crossing over occurs between them. Therefore, the alleles at the two loci will always be inherited together in the offspring, resulting in only parental phenotypes in the F₂of the appropriate test cross.

Question 19

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 which of the following? A)alternation of generations B)incomplete dominance C)hemizygosity D)independent assortment E)complete linkage

Accepted Answer

The equal numbers of the four groups (AaBb, Aabb, aaBb, aabb) suggest that the traits for A and B are segregating independently (i.e. independently assorting) from each other. This is consistent with Mendel's law of independent assortment.

Question 20

A ____ is all the genes on a single chromosome.
A)chromosomal conglomeration
B)gene loci line
C)genetic allele formation
D)linkage group
E)recombination group

Accepted Answer

A linkage group is all the genes on a single chromosome that are inherited together, meaning they are physically linked to each other on the chromosome.

Quiz 5: Chromosome Mapping in Eukaryotes

Which of the following scenarios would erroneously lead you to believe two genes reside on different chromosomes when they in fact are on the same chromosome?

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 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______ .

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: Compute the map distance between the light and straw loci.

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?

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

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 map units between the G and E loci.

Choose the true statement below.

Which of the following statements is true?

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 of the following?

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

Below is a diagram during crossing over.Describe the outcome.

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?

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

If complete linkage occurs,we expect ______.

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 which of the following?

A ____ is all the genes on a single chromosome.