Question 1

Which of the following statements describes genomic imprinting?

Accepted Answer

Genomic imprinting is a phenomenon where the expression of an allele depends on the gender of the parent from whom it is inherited. This occurs due to epigenetic modifications, such as DNA methylation, that stably alter the expression of specific genes in the male or female germ cells.

Question 2

Figure 15.4 
-The pedigree in Figure 15.4 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely

Accepted Answer

The answer of Figure 15.4 
-The pedigree in Figure 15.4...

Question 3

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore in which body systems would you expect most mitochondrial gene mutations to be exhibited?

Accepted Answer

The nervous and muscular systems are the most energy-intensive systems in the body and therefore require a high level of electron transport through the mitochondria. Mutations in mitochondrial genes involved in this process can lead to neurological and muscular disorders.

Question 4

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would then NOT be considered non-Mendelian?

Accepted Answer

The inheritance pattern described in choice D follows Mendel's laws, just with the variation that the gene is transmitted to males via the maternal line and to daughters via the paternal line. This pattern is known as mitochondrial inheritance and does not violate Mendel's laws. All other choices describe non-Mendelian inheritance patterns.

Question 5

The frequency of Down syndrome in the human population is most closely correlated with which of the following?

Accepted Answer

The frequency of Down syndrome is mostly correlated with the age of the mother, specifically women over the age of 35 have a higher risk of having a child with Down syndrome. Studies have shown that the chance of having a child with Down syndrome increases with the age of the mother because older eggs have a higher likelihood of improper chromosome division during meiosis. The age of the father has also been shown to have some correlation, but not as strongly as the age of the mother. The other options, frequency of new meiosis and exposure to environmental pollutants, have not been shown to have a significant correlation with the frequency of Down syndrome.

Question 6

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

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 7

Down syndrome has a frequency in the U.S. population of ~ 1/700 live births. In which of the following groups would you expect this to be significantly higher?

Accepted Answer

The answer of Down syndrome has a frequency in the...

Question 8

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

Accepted Answer

47, +21 is also known as Down Syndrome, which is associated with a range of health complications such as intellectual disability, heart defects, and increased risk of leukemia. While the other aneuploidies listed may also have health implications, Down Syndrome typically has the most significant impact on an individual's well-being.

Question 9

What is the source of the extra chromosome 21 in an individual with Down syndrome?

Accepted Answer

Down syndrome can be caused by nondisjunction, which is the failure of chromosomes to separate during meiosis, or translocation, where a part of chromosome 21 attaches to another chromosome. Nondisjunction or translocation can occur in either parent.

Question 10

Women with Turner syndrome have a genotype characterized as which of the following?

Accepted Answer

Turner syndrome is caused by a missing or incomplete X chromosome, leading to a karyotype of 45, X. The other answer choices are not associated with Turner syndrome.

Question 11

In order for chromosomes to undergo inversion or translocation, which of the following is required?

Accepted Answer

Chromosome breakage and rejoining are necessary for both inversion and translocation. Meiosis is also involved, but it is not the primary requirement. Point mutation, immunological insufficiency, and advanced maternal age are not directly related to chromosome rearrangements.

Question 12

At which phase(s)is it preferable to obtain chromosomes to prepare a karyotype?

Accepted Answer

Chromosomes are most condensed and visible during late prophase and metaphase, making them ideal for karyotyping.

Question 13

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because 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?

Accepted Answer

In a balanced translocation, the individual is phenotypically normal, but during gamete formation, there is a risk of producing unbalanced gametes. In this case, 1/4 of the sperm will be normal, 1/4 will carry the balanced translocation, and 1/2 will have duplications and deletions due to improper segregation during meiosis.

Question 14

In humans, male-pattern baldness is controlled by an autosomal gene that occurs in two allelic forms. Allele Hn determines nonbaldness, and allele Hb determines pattern baldness. In males, because of the presence of testosterone, allele Hb is dominant over Hn. If a man and woman both with genotype HnHb have a son, what is the chance that he will eventually be bald?

Accepted Answer

The answer of In humans, male-pattern baldness is controlled by...

Question 15

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

Accepted Answer

The translocation may result in the inappropriate expression of gene products, such as oncogenes, which can promote tumor growth and progression. Non-disjunction, a decrease in mitotic frequency and death of the cancer cells in the tumor are unlikely to make the cancer worse. Sensitivity of the immune system is not directly related to the presence of abnormal chromosomes in tumor cells.

Question 16

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?

Accepted Answer

Inversions can result in abnormal gametes due to crossing over during meiosis. This can lead to chromosomal abnormalities in offspring, including deletions or duplications. However, it is important to note that not all inversions result in abnormal gametes or offspring.

Question 17

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

Accepted Answer

The most probable cause of Down syndrome in this case is nondisjunction in gamete production, specifically in meiosis I, where an extra copy of chromosome 21 is present in one of the gametes. This is more likely to occur in older mothers, as the risk of nondisjunction increases with age. A translocation (choice B) would involve a rearrangement of chromosomes, and the parents would have been aware of this prior to the birth of their child. Inheriting a tendency for Down syndrome (choice A) is not a known cause of the condition. Nondisjunction in somatic cell production (choice C) does not result in a viable embryo, so it would not be a possible explanation for the birth of a child with Down syndrome.

Question 18

In 1956 Tijo and Levan first successfully counted human chromosomes. The reason it would have taken so many years to have done so would have included all but which of the following?

Accepted Answer

The structure of DNA discovered by Watson and Crick in 1953 is unrelated to the ability to count chromosomes. The other options relate to technical challenges in visualizing and distinguishing chromosomes.

Question 19

A nonreciprocal crossover causes which of the following products?

Accepted Answer

A nonreciprocal crossover involves unequal crossing over between homologous chromosome pairs. This can result in deletion of one region and duplication of another region, hence the products are deletion and duplication. Nondisjunction is the failure of homologous chromosomes to separate during meiosis, resulting in abnormal chromosome number in daughter cells. Therefore, options A, B, and C are incorrect. Option E is incorrect because it describes duplications and nondisjunction, neither of which would occur during a nonreciprocal crossover.

Question 20

Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?

Accepted Answer

The phenomenon described is chloroplast inheritance, where the color of the leaves is determined by the chloroplasts, which are inherited only from the maternal parent. Mitochondrial inheritance is also maternally inherited, but it refers to the inheritance of mitochondrial DNA. Genomic imprinting refers to the unequal expression of certain genes based on their parental origin. Infectious inheritance describes the transmission of genetic material through infectious agents, such as viruses. Sex-linkage refers to genes that are located on the sex chromosomes and are therefore inherited differently between males and females.

Quiz 15: The Chromosomal Basis of Inheritance