Question 1

Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following events might then occur to make the cancer worse?
A) an increase in nondisjunction
B) expression of inappropriate gene products
C) a decrease in mitotic frequency
D) failure of the cancer cells to multiply

Accepted Answer

When a gene is placed close to different control regions due to chromosomal abnormalities, it may start expressing inappropriate gene products which could make the cancer worse. A decrease in mitotic frequency or failure of the cancer cells to multiply may actually be beneficial in terms of controlling the growth of cancer cells. An increase in nondisjunction may further increase the chromosomal abnormalities, but it does not directly affect the expression of inappropriate gene products.

Question 2

Genomic imprinting is generally due to the addition of methyl (-CH₃) groups to C nucleotides and chemical histone changes to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following statements must be true?
A) Genes required for early development stages must not be imprinted.
B) Methylation of this kind must occur more in males than in females.
C) Methylation must be reversible in ovarian and testicular cells.
D) The imprints are transmitted only to gamete-producing cells.

Accepted Answer

Methylation must be reversible in ovarian and testicular cells to reset the imprinting pattern according to the sex of the parent transmitting the gene.

Question 3

Which of the following is an example of monosomy in humans?
A) Turner syndrome
B) Klinefelter syndrome
C) Down syndrome
D) trisomy X

Accepted Answer

Monosomy refers to the condition in which an individual has only one copy of a particular chromosome instead of the usual two. Turner syndrome is caused by the presence of only one X chromosome and is an example of monosomy in humans. Klinefelter syndrome (XXY), Down syndrome (Trisomy 21), and trisomy X (XXX) are examples of aneuploidy, in which an individual has an abnormal number of chromosomes.

Question 4

What is a syndrome?
A) a characteristic facial appearance
B) a trait that leads to cancer at some stage in life
C) a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
D) a specific characteristic that appears in conjunction with one specific aneuploidy

Accepted Answer

A syndrome is a group of traits that occur together and are typically associated with a particular chromosomal aberration or gene mutation. A characteristic facial appearance or a specific characteristic that appears in conjunction with one specific aneuploidy are typically part of a syndrome, but not the defining feature of a syndrome. A trait that leads to cancer at some stage in life is not necessarily part of a syndrome.

Question 5

German scientist Carl Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. What phenomenon explains this pattern of inheritance?
A) ribosome structure
B) inheritance of plastid genes
C) genomic imprinting
D) sex linkage

Accepted Answer

Inheritance of plastid genes refers to the transmission of genetic information from the chloroplasts and other organelles in the cytoplasm of the mother cell to the offspring. As the egg cell contributes almost all the cytoplasmic organelles to the zygote, the inheritance of variegated color on the leaves of plants can be linked to the maternal parent exclusively.

Question 6

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?
A) a female with masculine characteristics such as facial hair
B) an apparent male who is sterile
C) healthy female of slightly above-average height
D) a sterile female

Accepted Answer

This woman has Turner syndrome, a condition where one of the sex chromosomes is missing or partially missing. In this case, she has only one copy of the X chromosome, and two additional X chromosomes. While Turner syndrome can have a range of symptoms, including infertility and short stature, the presence of three X chromosomes is not typically associated with masculine characteristics or sterility. Therefore, option C is the most likely phenotype for this woman.

Question 7

During meiosis, a defect occurs in a cell that results in the failure of spindle microtubules binding at the kinetochores. Which of the following statements describes the most likely result of such a defect?
A) New microtubules with more effective binding capabilities to kinetochores will be synthesized to compensate for the defect.
B) Excessive cell divisions will occur resulting in cancerous tumors and an increase in the chromosome numbers known as polyploidy.
C) The defect will be bypassed in order to ensure normal chromosome distribution in the new cells.
D) The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy.

Accepted Answer

The failure of spindle microtubules to bind to kinetochores results in improper separation of chromosomes during meiosis, leading to gametes with an incorrect number of chromosomes, a condition known as aneuploidy. This can result in genetic disorders, developmental abnormalities, or even infertility. Option A is incorrect because it is unlikely that new microtubules will be synthesized to compensate for the defective ones. Option B is incorrect because excessive cell divisions will not occur as a result of this defect, and polyploidy is not a likely outcome either. Option C is incorrect because the defect cannot be bypassed, as proper attachment of spindle microtubules to kinetochores is critical for proper chromosome segregation.

Question 8

Use the following figure to answer the question.

The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely ________.
A) mitochondrial
B) sex-linked dominant
C) sex-linked recessive
D) autosomal dominant

Accepted Answer

The answer of Use the following figure to answer the...

Question 9

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
A) The woman inherited this tendency from her parents.
B) The mother had a chromosomal duplication.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One of the gametes in the mother most likely underwent nondisjunction during meiosis.

Accepted Answer

The most common cause of Down syndrome is nondisjunction during meiosis in one of the gametes, typically in the mother. The risk of nondisjunction increases with maternal age, which in this case is 39 years old. Therefore, option D is the most likely cause of the child's condition. The other options are less likely to be the cause of Down syndrome in this case.

Question 10

Which of the following statements is generally true of aneuploidies in newborns?
A) A monosomy is more frequent than a trisomy.
B) Monosomy X is the only viable monosomy known to occur in humans.
C) Human aneuploidy usually conveys an adaptive advantage in humans.
D) An aneuploidy resulting in the deletion of a chromosome segment is less serious than a duplication.

Accepted Answer

Monosomy X, also known as Turner syndrome, is the only viable monosomy known to occur in humans. Other monosomies, such as monosomy 21 or 18, typically result in miscarriage or stillbirth.

(A) is incorrect because trisomies are actually more frequent than monosomies in newborns.
(C) is incorrect because aneuploidies generally convey a disadvantage and can result in developmental abnormalities or genetic disorders.
(D) is incorrect because both deletions and duplications of chromosome segments can have serious consequences, depending on the genes affected.

Question 11

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4, which has been exchanged with a portion of his chromosome 12. Although his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?
A) One-quarter will carry the two normal chromosomes, 4 and 12, one-quarter will have only the two translocation chromosomes and no normal chromosomes 4 and 12, and half will have one normal and one translocated chromosome.
B) All will carry the same translocation as the father.
C) None will carry the translocation.
D) Half will be normal, and the rest will have the father's translocation.

Accepted Answer

The father's translocation involves a portion of chromosome 4 and a portion of chromosome 12. As a result, there are three possibilities for the offspring's chromosomes: normal chromosomes 4 and 12 (from the mother) and normal chromosomes 4 and 12 (from the father); translocated chromosomes 4 and 12 (from the father); or one normal chromosome 4 (from the mother or the father) and one translocated chromosome 4/12 (from the father). The probability of each of these three possibilities is equal, which means that one-quarter of the offspring will carry the two normal chromosomes, one-quarter will have only the two translocation chromosomes and no normal chromosomes 4 and 12, and half will have one normal and one translocated chromosome. Therefore, the prognosis regarding the father's sperm is that half will be normal, and the rest will have the father's translocation.

Question 12

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this type of chromosomal alteration called?
A) deletion
B) inversion
C) translocation
D) duplication

Accepted Answer

This type of chromosomal alteration is called translocation, where a fragment from one chromosome breaks off and joins a nonhomologous chromosome. Deletion involves the loss of a segment of a chromosome, inversion involves the reversing of the direction of a segment within a chromosome, and duplication involves the doubling of a segment within a chromosome.

Question 13

A certain kind of snail can have a right-handed direction of shell coiling (DD or Dd) or left-handed coiling (dd). However, if direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?
A) 1/2 Dd:1/2 dd; all right-coiling
B) all Dd; all right-coiling
C) 1/2 Dd: 1/2 dd; half right-coiling and half left-coiling
D) all Dd; half right-coiling and half left-coiling

Accepted Answer

The offspring will have genotypes 1/2 Dd and 1/2 dd. However, since the direction of coiling is determined by the mother's genotype, all offspring will exhibit right-coiling due to the Dd mother's influence.

Question 14

Which of the following correctly describes a Philadelphia chromosome?
A) a human chromosome 22 that has had a specific translocation
B) a human chromosome 9 that is found only in one type of cancer
C) an animal chromosome found primarily in the mid-Atlantic area of the United States
D) a chromosome found only in mitochondria

Accepted Answer

The Philadelphia chromosome is a human chromosome 22 that has had a specific translocation involving a piece of chromosome 9. This translocation is associated with a type of blood cancer called chronic myelogenous leukemia (CML).

Question 15

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?
A) 47, trisomy 21
B) 47, XXY
C) 47, XXX
D) 45, X

Accepted Answer

Trisomy 21, also known as Down syndrome, is caused by the presence of an extra copy of chromosome 21. This condition can cause intellectual disability, characteristic physical features, and a higher risk of heart defects and other health problems. It is generally considered to have the most severe impact on the health of the individual among the given options.

Question 16

Which of the following statements correctly describes what happens to a chromosome after a nonreciprocal translocation occurs?
A) A deletion of part of the chromosome occurs.
B) A duplication of part of the chromosome occurs.
C) Nondisjunction of pairs of homologous occurs.
D) A chromosome transfers a fragment but receives none in return.

Accepted Answer

In a nonreciprocal translocation, a fragment of one chromosome is transferred to another chromosome, but no fragment is received in return. Therefore, choice D is the correct answer. Choices A and B are incorrect because they describe outcomes of other chromosomal mutations, such as deletions and duplications. Choice C is incorrect because nondisjunction is a failure of chromosomes to properly separate during meiosis, and does not directly relate to a translocation.

Question 17

Inheritance patterns cannot always be explained by Mendel's models of inheritance. If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?
A) n + 1; n + 1; n - 1; n - 1
B) n + 1; n - 1; n; n
C) n + 1; n - 1; n - 1; n - 1
D) n + 1; n + 1; n; n

Accepted Answer

When homologous chromosomes fail to separate during meiosis I, it results in two gametes with an extra chromosome (n + 1) and two gametes missing a chromosome (n - 1).

Question 18

Mitochondrial DNA is primarily involved in coding for proteins needed for protein complexes of the electron transport chain and ATP synthase. Therefore, mutations in mitochondrial genes would most affect which of the following processes?
A) DNA synthesis in cells of the immune system
B) the movement of oxygen into erythrocytes
C) generation of ATP in muscle cells
D) the storage of urine in the urinary bladder

Accepted Answer

Mitochondrial DNA is responsible for coding proteins involved in the electron transport chain and ATP synthase. Both of these processes are involved in the generation of ATP, which is primarily done in muscle cells. Therefore, mutations in mitochondrial genes would most affect the process of generating ATP in muscle cells.

Quiz 15: The Chromosomal Basis of Inheritance

Abnormal chromosomes are frequently found in malignant tumors. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following events might then occur to make the cancer worse?

Genomic imprinting is generally due to the addition of methyl (-CH₃) groups to C nucleotides and chemical histone changes to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following statements must be true?

Which of the following is an example of monosomy in humans?

What is a syndrome?

German scientist Carl Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. What phenomenon explains this pattern of inheritance?

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?

During meiosis, a defect occurs in a cell that results in the failure of spindle microtubules binding at the kinetochores. Which of the following statements describes the most likely result of such a defect?

Use the following figure to answer the question. The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely ________.

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?

Which of the following statements is generally true of aneuploidies in newborns?

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this type of chromosomal alteration called?

Which of the following correctly describes a Philadelphia chromosome?

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

Which of the following statements correctly describes what happens to a chromosome after a nonreciprocal translocation occurs?

Inheritance patterns cannot always be explained by Mendel's models of inheritance. If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n) ?

Mitochondrial DNA is primarily involved in coding for proteins needed for protein complexes of the electron transport chain and ATP synthase. Therefore, mutations in mitochondrial genes would most affect which of the following processes?