Question 1

A woman has a condition where all of her gametes undergo nondisjunction of chromosome 21 in meiosis I, but meiosis II proceeds normally.She mates with a man who produces all normal gametes.What is the probability that the fertilized egg will develop into a child with Down syndrome? Assume that all gametes and zygotes are viable.
A)1/8
B)1/4
C)1/3
D)1/2
E)0

Accepted Answer

Nondisjunction of chromosome 21 in meiosis I in the woman's gametes means each of her eggs will have an extra chromosome 21. When fertilized by a normal sperm from the man, all resulting zygotes will have three copies of chromosome 21, leading to Down syndrome.

Question 2

A plant species has 2n = 18 chromosomes.How many chromosomes would you expect to find in a tetrasomic individual of this species?
A)17
B)19
C)20
D)22
E)36

Accepted Answer

A tetrasomic individual would have four copies of one chromosome, which would make the total number of chromosomes in the individual 20 (18 + 2).

Question 3

A man has a condition where all of his gametes undergo nondisjunction of the sex chromosomes in meiosis I, but meiosis II proceeds normally.He mates with a woman who produces all normal gametes.What is the probability that the fertilized egg will develop into a child with Klinefelter syndrome (XXY)? Assume that all gametes and zygotes are viable.
A)1/8
B)1/4
C)1/3
D)1/2
E)0

Accepted Answer

The answer of A man has a condition where all...

Question 4

Wild-type Arabidopsis has five chromosomes (2n = 10).Trisomic plants are designated as Tr followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1.Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing)are possible at meiosis, what proportion of the progeny from the cross Tr1 × Tr1 will have a wild-type chromosomal complement?
A)1/2
B)1/3
C)1/4
D)1/9
E)1/81

Accepted Answer

In a Tr1 × Tr1 cross, both parents have an extra copy of chromosome 1, making their genotype 2n+1 for that chromosome. During meiosis, the chromosomes can segregate in several ways, but for a progeny to have a wild-type chromosomal complement (2n = 10), one gamete must contribute the normal two copies of chromosome 1, and the other must contribute only one copy. The probability of producing a gamete with two copies from a trisomic parent (2n+1) is 1/3, as the three copies of chromosome 1 can segregate as (2:1) or (1:2), with two equally likely configurations out of six total possibilities resulting in a gamete with two chromosomes. Therefore, the probability that one parent produces a gamete with two copies and the other produces a gamete with one copy is (1/3) * (1/3) = 1/9.

Question 5

What would be the consequence of a diploid gamete (resulting from meiotic nondisjunction)being fertilized by a haploid gamete from the same species?
A)Allodiploid
B)Allotriploid
C)Autotriploid
D)Allotetraploid
E)Autotetraploid

Accepted Answer

Autotriploid organisms result from the fertilization of a diploid gamete with a haploid gamete, leading to an organism with three sets of chromosomes, all from the same species.

Question 6

A man has a condition where all of his gametes undergo meiosis I normally, but there is nondisjunction of the sex chromosomes in every meiosis II.He mates with a woman who produces all normal gametes.What is the probability that the fertilized egg will develop into a child with Klinefelter syndrome (XXY)? Assume that all gametes and zygotes are viable.
A)1/8
B)1/4
C)1/3
D)1/2
E)0

Accepted Answer

The answer of A man has a condition where all...

Question 7

Which form of aneuploidy causes primary Down syndrome?
A)Nullisomy
B)Monosomy
C)Disomy
D)Trisomy
E)Tetrasomy

Accepted Answer

Trisomy, specifically trisomy of chromosome 21, causes primary Down syndrome.

Question 8

Which of the following is a form of aneuploidy in which four members of the same homologous pair are present?
A)Nullisomy
B)Monosomy
C)Disomy
D)Trisomy
E)Tetrasomy

Accepted Answer

Tetrasomy is the form of aneuploidy in which four members of the same homologous pair are present. Nullisomy is the absence of both members of a homologous pair, monosomy is the presence of only one member of a homologous pair, disomy is the normal condition with two members of a homologous pair, and trisomy is the presence of three members of a homologous pair.

Question 9

Which type of polyploidy is synonymous with amphidiploid?
A)Allodiploid
B)Allotriploid
C)Autotriploid
D)Allotetraploid
E)Autotetraploid

Accepted Answer

Amphidiploid is the same as allotetraploid because it is formed from the hybridization of two diploid species.

Question 10

Which of the following is NOT a form of aneuploidy in diploid organisms?
A)Nullisomy
B)Monosomy
C)Disomy
D)Trisomy
E)Tetrasomy

Accepted Answer

Disomy is the normal state of having two copies of each chromosome in a diploid organism, not a form of aneuploidy. Aneuploidy refers to an abnormal number of chromosomes, and disomy represents the expected number.

Question 11

Wild-type Arabidopsis has five chromosomes (2n = 10).Trisomic plants are designated as Tr followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1.Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing)are possible at meiosis, what proportion of the progeny from the cross Tr1;Tr2 × Tr1;Tr2 will have a wild-type chromosomal complement?
A)1/2
B)1/3
C)1/4
D)1/9
E)1/81

Accepted Answer

Each parent has an extra chromosome 1 and an extra chromosome 2, leading to a complex assortment during meiosis. The probability of both parents contributing the normal set of chromosomes (without the extra ones) is (1/3 for chromosome 1) * (1/3 for chromosome 2) = 1/9. Since both parents must contribute normally, the probability is (1/9) * (1/9) = 1/81.

Question 12

Wild-type Arabidopsis has five chromosomes (2n = 10).Trisomic plants are designated as Tr followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1.Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing)are possible at meiosis, what proportion of the progeny from the cross wt × Tr1;Tr2 will have a wild-type chromosomal complement?
A)1/2
B)1/3
C)1/4
D)1/9
E)1/81

Accepted Answer

In the cross between a wild-type (wt) Arabidopsis (with a normal diploid chromosome number of 2n = 10) and a plant trisomic for chromosomes 1 and 2 (Tr1;Tr2), the trisomic plant has one extra copy of chromosomes 1 and 2, making its chromosome number 2n + 1 + 1 = 12. During gamete formation in the trisomic plant, various combinations of chromosomes can be produced, including those with an extra chromosome 1, an extra chromosome 2, both extra chromosomes, or neither. For progeny to have a wild-type chromosomal complement (2n = 10), they must receive gametes from the trisomic parent that do not contain any extra chromosomes. Given that all possible pairing configurations are possible at meiosis, including nonpairing, the chance of forming a gamete without any extra chromosomes (thus leading to a wild-type progeny when fertilized by a wild-type gamete) is significantly reduced. Considering the multiple possible disjunctions and the need for the specific outcome where no extra chromosomes are included in the gamete, the probability is 1/9, reflecting the complexity of achieving a specific gamete composition from a trisomic parent.

Question 13

What is responsible for primary Down syndrome?
A)Disomy
B)Inversion
C)Nondisjunction
D)Polyploidy
E)Translocation

Accepted Answer

Primary Down syndrome is caused by nondisjunction, a failure of chromosome 21 to separate properly during meiosis. This results in an extra copy of chromosome 21 and leads to the characteristic symptoms of Down syndrome.

Question 14

Which type of chromosome mutation is responsible for familial Down syndrome?
A)Disomy
B)Inversion
C)Nondisjunction
D)Polyploidy
E)Translocation

Accepted Answer

Familial Down syndrome is caused by a translocation of a segment of chromosome 21 onto another chromosome. This results in three copies of chromosome 21 in some cells, causing the characteristic features of Down syndrome.

Question 15

Wild-type Arabidopsis has five chromosomes (2n = 10).Trisomic plants are designated as Tr followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1.Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing)are possible at meiosis, what proportion of the progeny from the cross wt × Tr1 will have a wild-type chromosomal complement?
A)1/2
B)1/3
C)1/4
D)1/9
E)1/81

Accepted Answer

In the cross wt (2n=10) × Tr1 (2n=11), the Tr1 parent can produce gametes with either 5 or 6 chromosomes. The wild-type parent produces gametes with 5 chromosomes. The progeny will have a wild-type chromosomal complement (2n=10) only if the Tr1 parent contributes a gamete with 5 chromosomes. The probability of this happening is 1/3, as the Tr1 parent can produce three types of gametes: two with 5 chromosomes and one with 6 chromosomes.

Question 16

A newly discovered species of dung beetle has 2n = 16 chromosomes.It mates with a closely related beetle species that has 2n = 12 chromosomes.How many chromosomes would there be in an allotriploid beetle produced from this cross?
A)13 or 17
B)19 or 25
C)18 or 24
D)20 or 22
E)36 or 48

Accepted Answer

An allotriploid is formed when a diploid and a tetraploid mate, resulting in an offspring with three sets of chromosomes. In this case, the newly discovered dung beetle has two sets of chromosomes (2n = 16) and the closely related species has two sets of chromosomes (2n = 12). 
To create an allotriploid, we need to mate these two species to produce an offspring with three sets of chromosomes. The simplest way to do this is to cross a haploid gamete from the first species (n = 8) with a diploid gamete from the second species (2n = 12). The resulting zygote will have 2n = 28 chromosomes, which is triploid (3n). 
However, this offspring will not be viable because the chromosomes from the two species cannot pair up properly during meiosis. Some of the chromosomes will be unable to pair and segregate correctly, leading to gametes with the wrong number of chromosomes. To create a viable allotriploid, we need to reduce the number of chromosomes to 2n = 30 or 2n = 33. 
The possible combinations of chromosomes that add up to 30 or 33 are:
- 16 + 12 + 2 = 30
- 16 + 12 + 5 = 33
This means that the allotriploid dung beetle could have either 20 (2n = 20) or 22 (2n = 22) chromosomes.

Question 17

A man has a condition where all of his gametes undergo nondisjunction of the sex chromosomes in meiosis I, but meiosis II proceeds normally.He mates with a woman who produces all normal gametes.What is the probability that the fertilized egg will develop into a child with Turner syndrome (XO)? Assume that all gametes and zygotes are viable.
A)1/8
B)1/4
C)1/3
D)1/2
E)0

Accepted Answer

The answer of A man has a condition where all...

Question 18

What type of organism results from the hybridization of a haploid gamete from one species with a diploid gamete from a different species?
A)Allodiploid
B)Allotriploid
C)Autotriploid
D)Allotetraploid
E)Autotetraploid

Accepted Answer

Allotriploid organisms result from the hybridization of a haploid gamete (n) from one species with a diploid gamete (2n) from a different species, combining to form a triploid organism (3n).

Question 19

An explorer stumbled upon a remote valley and found plants that produced a colorful, sweet fruit.Many of these plants were autopolyploid and came in varieties that differed by their ploidy and the size of fruit that was produced.Which of the following plant genomes would MOST likely produce sterile plants?
A)Diploid (2n)
B)Triploid (3n)
C)Tetraploid (4n)
D)Hexaploid (6n)
E)Octaploid (8n)

Accepted Answer

Triploid plants are often sterile because they have an odd number of chromosomes, which can create problems during meiosis and result in non-functional gametes.

Question 20

An explorer stumbled upon a remote valley and found plants that produced a colorful, sweet fruit.Many of these plants were autopolyploid and came in varieties that differed by their ploidy and the size of fruit that was produced.Which of the following plant genomes would MOST likely produce the largest fruit?
A)Diploid (2n)
B)Triploid (3n)
C)Tetraploid (4n)
D)Hexaploid (6n)
E)Octaploid (8n)

Accepted Answer

Generally, polyploid organisms have larger cells and are larger overall than their diploid counterparts, and this often translates to larger fruits. Therefore, the plant with the highest ploidy level of the options given (8n) is most likely to produce the largest fruit.

Quiz 6: Chromosome Variation

A plant species has 2n = 18 chromosomes.How many chromosomes would you expect to find in a tetrasomic individual of this species?

What would be the consequence of a diploid gamete (resulting from meiotic nondisjunction) being fertilized by a haploid gamete from the same species?

Which form of aneuploidy causes primary Down syndrome?

Which of the following is a form of aneuploidy in which four members of the same homologous pair are present?

Which type of polyploidy is synonymous with amphidiploid?

Which of the following is NOT a form of aneuploidy in diploid organisms?

What is responsible for primary Down syndrome?

Which type of chromosome mutation is responsible for familial Down syndrome?

A newly discovered species of dung beetle has 2n = 16 chromosomes.It mates with a closely related beetle species that has 2n = 12 chromosomes.How many chromosomes would there be in an allotriploid beetle produced from this cross?

What type of organism results from the hybridization of a haploid gamete from one species with a diploid gamete from a different species?