Question 1

What degree of relationship to each other are half-siblings?

Accepted Answer

B

Question 2

If an uncle has children with his niece, which of the following genetic terms is used to describe this relationship?

Accepted Answer

Consanguinity refers to the genetic relationship between individuals who share a common ancestor, making it the correct term to describe the genetic relationship between an uncle and his niece when they have children together.

Question 3

What is the term used to describe the patient who first brings a family to a geneticist's attention?

Accepted Answer

Proband is the term used to describe the individual who first brings a genetic disorder to the attention of the medical community, often by being the first diagnosed case in a family.

Question 4

Which of the following is a likely explanation that a male could survive an X-linked dominant, male lethal disorder?

Accepted Answer

A male with 47, XXY karyotype has an extra X chromosome, which could allow him to survive an X-linked dominant, male lethal disorder because the presence of the second X chromosome can compensate for the lethal mutation.

Question 5

In certain proteins, expansion of a tract of which amino acid is associated with various genetic forms of progressive neurodegeneration?

Accepted Answer

Expansion of a tract of glutamine (due to CAG repeat expansion in the DNA) is associated with various genetic forms of progressive neurodegeneration, such as Huntington's disease. This phenomenon is known as a polyglutamine (polyQ) disease.

Question 6

Which of the following terms refers to the fact that different people with the same genotype can have variation in phenotype?

Accepted Answer

Variable expressivity refers to the phenomenon where individuals with the same genotype may display a range of phenotypes, indicating that the expression of the genotype can vary in degree or kind among individuals.

Question 7

Trinucleotide repeat alleles that are not associated with the disease phenotype but that can expand during meiosis are known as:

Accepted Answer

Permutations in the context of genetic terminology are often referred to as "premutations," a term used to describe trinucleotide repeat alleles that are not yet large enough to cause disease but can expand in future generations to a full mutation, which is disease-causing.

Question 8

For an autosomal dominant disease, if two affected parents have a child, what is most likely the risk of passing on the disorder?

Accepted Answer

In an autosomal dominant disease, each affected parent has at least one dominant allele for the disease. When both parents are affected, their genotypes could be either heterozygous (Aa) or homozygous dominant (AA). The possible offspring genotypes are AA (affected), Aa (affected), and aa (unaffected). The only way for the child to not inherit the disease is if both parents pass on the recessive allele (a), which occurs in 1 out of 4 scenarios if both parents are heterozygous. Therefore, there is a 75% chance (3 out of 4 scenarios) that the child will inherit the disease.

Question 9

Which of the following are true about mitochondrial inheritance?

Accepted Answer

All of the statements about mitochondrial inheritance are true. Heteroplasmy refers to the presence of more than one type of mitochondrial DNA within a cell. Mitochondria do segregate randomly during cell division, which can affect the distribution of different mitochondrial genotypes among cells. Mitochondrial inheritance is primarily maternal, meaning that the mitochondria in the offspring come from the mother's egg cell. Lastly, it is accurate that there are approximately 1000 mitochondrial DNA molecules per cell, though this number can vary depending on the cell type and its energy demands.

Question 10

A process that can greatly affect the presentation of an X-linked phenotype in carrier females is:

Accepted Answer

X-inactivation is a process that occurs in females where one of the two X chromosomes is randomly inactivated in each cell. This can greatly affect the presentation of an X-linked phenotype in carrier females because if the X chromosome carrying the mutant allele is inactivated, the phenotype may not be expressed, whereas if the X chromosome with the normal allele is inactivated, the phenotype may be expressed.

Question 11

Which of the following terms refers to a set of alleles that is inherited together on a chromosome?

Accepted Answer

Haplotype refers to a set of alleles on a chromosome that are inherited together from a single parent, indicating a specific combination of genetic markers closely linked on a chromosome.

Question 12

Unstable trinucleotide repeat alleles can be observed to expand in which of the following situations?

Accepted Answer

The answer of Unstable trinucleotide repeat alleles can be observed...

Question 13

Genetic anticipation is associated with:

Accepted Answer

Genetic anticipation is associated with trinucleotide repeat instability, where the length of a repeated sequence in the DNA increases with each generation, often leading to earlier onset and more severe manifestation of genetic disorders.

Question 14

When a set of parents has a child affected by an autosomal recessive disorder, the most likely recurrence risk is:

Accepted Answer

In autosomal recessive disorders, both parents must be carriers of the defective gene. Each child has a 25% chance of inheriting both copies of the defective gene, one from each parent, which would result in the disorder.

Question 15

What genetic force leads to the variability in the percentage of mutant mtDNA molecules that are present in the children of a mother who exhibits heteroplasmy for the mutation?

Accepted Answer

Genetic bottleneck refers to the sharp reduction in the size of a population due to environmental events or other changes, leading to a limited number of individuals passing on their genetic material to the next generation. In the context of mitochondrial DNA (mtDNA), during the process of oogenesis (egg formation), a reduction in the number of mitochondria occurs, which can lead to a significant variation in the proportion of mutant versus normal mtDNA molecules passed on to the offspring. This phenomenon explains the variability in the percentage of mutant mtDNA molecules in children of a mother with heteroplasmy, as only a subset of the mother's mtDNA is transmitted, potentially altering the ratio of mutant to wild-type mtDNA in the next generation.

Question 16

What is the most likely explanation for a set of unaffected parents having two children with a highly-penetrant, autosomal dominant disorder?

Accepted Answer

Germline mosaicism in one of the parents is the most likely explanation for unaffected parents having two children with a highly-penetrant, autosomal dominant disorder. This condition occurs when some of the parent's germ cells (sperm or eggs) carry a genetic mutation, but the mutation is not present in the parent's somatic (body) cells, making the parent unaffected by the disorder but capable of passing the mutation to their offspring.

Question 17

Which type of mitochondrial mutation is NOT passed from an affected mother to her child when the mother exhibits heteroplasmy for the mutation?

Accepted Answer

The answer of Which type of mitochondrial mutation is NOT...

Question 18

What is the risk for hemophilia A in the grandsons if their paternal grandfather is a hemophiliac?

Accepted Answer

Hemophilia A is an X-linked recessive disorder. A paternal grandfather cannot pass his X chromosome to his grandsons; he passes it to his daughters, who may become carriers. The grandsons inherit their X chromosome from their mother, not their paternal grandfather.

Question 19

Anticipation is the finding in a genetic disorder that:

Accepted Answer

Anticipation refers to the phenomenon where, in certain genetic disorders, the severity of the disorder increases and the age of onset decreases in successive generations. This is often observed in disorders caused by trinucleotide repeat expansions, such as Huntington's disease and myotonic dystrophy.

Question 20

Heteroplasmy is associated with:

Accepted Answer

Heteroplasmy refers to the presence of more than one type of mitochondrial DNA within a cell or individual, making it challenging to predict the exact mitochondrial DNA composition in offspring, thus complicating prenatal diagnosis.

Quiz 7: Patterns of Single-Gene Inheritance