Question 1

Which of the following is an example of an X-linked recessive genetic trait?

Accepted Answer

Red-green colorblindness is an X-linked recessive genetic trait, meaning that the gene responsible for the trait is located on the X chromosome and a female carrier has a 50% chance of passing the trait on to her male offspring, who only inherit one X chromosome. Porphyria, familial hypercholesterolemia, Marfan syndrome, and achondroplasia are not X-linked recessive genetic traits.

Question 2

Which of the following is true about the genetic disease cystic fibrosis (CF)?

Accepted Answer

Cystic fibrosis (CF) demonstrates autosomal recessive inheritance. This means that an individual must inherit two copies of the mutated gene (one from each parent) to develop CF. If an individual inherits only one mutated gene, they are a carrier of the disease but do not have symptoms.

The other choices are incorrect: 
B) CF does not increase the risk of skin cancer, although individuals with CF may have increased sensitivity to sunlight due to medications taken for treatment. 
C) CF does not directly produce abnormal blood cells. 
D) CF does not cause excessive accumulation of phenylalanine in the blood; this is a symptom of another genetic disease called phenylketonuria. 
E) CF does not cause improper metabolism in nerve cells.

Question 3

What is the distinctive pattern of inheritance found for X-linked recessive traits?

Accepted Answer

X-linked recessive traits are carried on the X chromosome, and because males only have one X chromosome (hemizygous) and females have two, the inheritance pattern is distinct. Hemizygous males (with only one X chromosome) and homozygous females (with two affected X chromosomes) are affected, while heterozygous females are usually carriers and not affected. Carriers have one affected X chromosome and one normal X chromosome, and they do not show the trait unless they have two copies of the recessive allele.

Question 4

Which of the following is true about the genetic disease familial hypercholesterolemia (FH)?

Accepted Answer

Familial hypercholesterolemia (FH) is a condition characterized by very high levels of cholesterol in the blood.

Answer: E
 FH is inherited as an X-linked dominant or X-linked recessive trait depending on the specific genetic mutation involved. However, X-linked dominant inheritance is the most common form.

Question 5

Mendel's law of independent assortment states that

Accepted Answer

Mendel's law of independent assortment states that each pair of alleles segregates independently of other pairs of alleles during meiosis. This means that the inheritance of one gene does not affect the inheritance of another gene, and the assortment of alleles for one gene is independent of the assortment for another gene. This also means that the combination of alleles a gamete receives for one gene is random and does not depend on the combination the gamete receives for other genes.

Question 6

Genetic counselors typically construct pedigrees

Accepted Answer

Genetic counselors typically construct pedigrees when an individual requests genetic counseling, as it helps identify patterns of inheritance and assess the risk of passing on genetic conditions in the family. Pedigrees are not only limited to families with members who have cystic fibrosis, and they are not used in criminal trials.

Question 7

A phenotype is

Accepted Answer

A phenotype is the physical appearance of an organism, which is determined by both its genetic make-up and its environment.

Question 8

A trait

Accepted Answer

A trait is a characteristic that can be passed from parent to offspring through genes, so A is the correct answer. B is incorrect because traits can be inherited from both parents, regardless of their sex. C is false because traits can have multiple forms or variations. D and E are both false because traits can be expressed in individuals who are either homozygous or heterozygous for that trait.

Question 9

Huntington disease (HD)

Accepted Answer

Huntington disease is caused by a dominant inheritance pattern, meaning if a person inherits the abnormal gene from one parent, they will develop the disease. It usually manifests in middle age, but can sometimes affect individuals in their 20s or 30s. HD is a progressive disease that can lead to death, usually within 10 to 30 years after onset.

Question 10

A recessive allele is

Accepted Answer

A recessive allele is an allele that is only expressed in the phenotype of an individual when it is paired with another identical recessive allele. In other words, its presence can be hidden or masked by the presence of a dominant allele.

Question 11

Mendel's law of segregation states that

Accepted Answer

Mendel's law of segregation states that the two copies of a gene separate from each other during meiosis. This means that each gamete will receive only one copy of the gene.

Question 12

A genotype is

Accepted Answer

A genotype refers to the genetic make-up of an organism, including all of its inherited genes and variations. It can be expressed in terms of alleles, which are different versions of the same gene. This is distinct from phenotype, which refers to the observable physical or behavioral characteristics of an organism. Genotypes can be influenced by a variety of factors, including genetic mutation, environmental factors, and genetic recombination during reproduction.

Question 13

Which of the following properties is characteristic of an autosomal recessive pattern of inheritance?

Accepted Answer

Autosomal recessive disorders affect male and female children in roughly equal numbers. This is because individuals must inherit two copies of the disease allele (one from each parent) in order to be affected. Each parent who is a carrier (has one copy of the disease allele and one normal allele) has a 50% chance of passing on the disease allele to each of their children, regardless of the child's sex. Therefore, the likelihood of a male or female child being affected is the same.

Question 14

Which of the following is an example of an autosomal recessive genetic disorder?

Accepted Answer

Cystic fibrosis is an example of an autosomal recessive genetic disorder. It is caused by mutations in the CFTR gene, and individuals must inherit two copies of the mutated gene (one from each parent) to develop the disease. Hemophilia A is an X-linked recessive disorder, Duchenne muscular dystrophy is an X-linked recessive disorder, Marfan syndrome is an autosomal dominant disorder, and brachydactyly can be caused by multiple genetic factors.

Question 15

Sickle-cell is

Accepted Answer

Sickle-cell is caused by abnormal hemoglobin molecules. Other options are incorrect, as sickle-cell is more commonly found in people of African descent, is inherited as a recessive disorder, is associated with various health problems, and occurs equally in males and females.

Question 16

Which of the following is an example of an autosomal dominant genetic disorder?

Accepted Answer

Porphyria is an example of an autosomal dominant genetic disorder, in which a single copy of the mutated gene is enough to cause the disease.

Question 17

Which of the following statements is true concerning a homozygote?

Accepted Answer

A homozygote is an individual that has the same two alleles for a particular gene. This means that both copies of the gene are the same, which is represented by the term "homozygous." Therefore, statement A is true. Statement B is incorrect because homozygotes have two copies of the same gene. Statement C is also incorrect because there is no gender bias in heterozygosity/homozogosity. Statement D is incorrect because a homozygote has two of the same alleles, not two different alleles. Statement E is not always true because the phenotype of an individual depends on the specific traits and alleles involved.

Question 18

A dominant allele is

Accepted Answer

A dominant allele is one that is expressed even when only one copy is present in a heterozygous individual. It masks the presence of a recessive allele. So, option A is the correct answer.

Question 19

Huntington disease is caused by

Accepted Answer

Huntington disease is caused by the accumulation of a defective protein called huntingtin, which damages and ultimately kills nerve cells in the brain. It is inherited in an autosomal dominant manner, meaning that only one copy of the defective gene is needed for the disease to develop.

Question 20

Which is of the following statements is true about sex-linked traits?

Accepted Answer

Fathers donate their Y chromosome to their sons and their X chromosome to their daughters, meaning sons cannot inherit an X chromosome from their father.

Quiz 4: How Genes Are Transmitted From Generation to Generation