Question 1

Alport syndrome, a dominantly inherited X-linked disorder, is characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. A mother with alport disease, whose father was unaffected, marries an unaffected man. What are the chances that she would give birth to a son with alport syndrome?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Since Alport syndrome is an X-linked dominant condition, a mother with the disease has a 50% chance of passing the affected X chromosome to each child. Sons who inherit the affected X chromosome will have the disease, so there's a 50% chance a son will be affected.

Question 2

Which genetic disorder is associated with an irregular shape of the red blood cells?
A) sickle-cell disease
B) Marfan syndrome
C) Huntington disease
D) phenylketonuria (PKU)
E) cystic fibrosis (CF)

Accepted Answer

Sickle-cell disease is caused by a mutation in the gene that codes for hemoglobin, which results in an irregular shape of the red blood cells. This can lead to blockages in blood vessels, causing pain, organ damage, and increased risk of infections.

Question 3

Both parents are heterozygous for Tay-Sachs disease (an autosomal recessive disorder). Three children in a row were born with Tay-Sachs disease. What is the chance that a fourth child will have Tay-Sachs disease?
A) 25%
B) 0%
C) 50%
D) 75%
E) 100%

Accepted Answer

The chance that a child will inherit Tay-Sachs disease when both parents are heterozygous is 25% for each pregnancy, independent of previous outcomes.

Question 4

In fruit flies, red-eyes are dominant to white-eyes. In addition, eye color is a sex-linked trait. If a homozygous red-eyed female Drosophila mates with a red-eyed male Drosophila. What proportion of the female offspring will have white eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Since the trait is sex-linked and the female is homozygous for the dominant red-eye trait, all female offspring will inherit a red-eye allele from her and thus cannot have white eyes.

Question 5

Which of the following is an autosomal dominant disorder?
A) Huntington's disease
B) sickle-cell disease
C) alkaptonuria
D) cystic fibrosis
E) methemoglobinemia

Accepted Answer

Huntington's disease is an autosomal dominant disorder, meaning that only one copy of the defective gene, inherited from one parent, is necessary for the disease to develop.

Question 6

A blue-eyed, left-handed woman marries a brown-eyed, right-handed man who is heterozygous for both of histraits. If blue eyes and left-handedness are recessive, how many different phenotypes are possible in their children?
A) four
B) three
C) two
D) one
E) five

Accepted Answer

The children can have four different phenotypes regarding eye color and handedness: blue-eyed and left-handed, blue-eyed and right-handed, brown-eyed and left-handed, and brown-eyed and right-handed. This is because each trait has two possible phenotypes (dominant and recessive), and they assort independently.

Question 7

Red-green color blindness is a recessive X-linked trait. If a female is red-green color-blind, which of the following is true?
A) Her mother must be color-blind.
B) Both her parents must be color-blind.
C) Both her parents are carriers of the recessive allele.
D) Her father must be color-blind.
E) Women cannot exhibit red-green color blindness because they have two X chromosomes.

Accepted Answer

Since red-green color blindness is a recessive X-linked trait, a female (XX) must inherit two copies of the recessive allele to express the trait. She inherits one X chromosome from her mother and one from her father. If she is color-blind, she must have received the recessive allele on the X chromosome from her father, making him color-blind. Her mother can be a carrier or color-blind, but must at least carry one recessive allele.

Question 8

A woman with type AB blood marries a man who is heterozygous for type B blood. If they have children, what are all the possible blood types for the children?
A) AB only
B) AB, AA, AO, and BO
C) AB, BB, AO, and BO
D) BB only
E) AA, BB, and AB

Accepted Answer

The woman with AB blood can contribute either an A or a B allele, and the man with heterozygous type B blood (genotype BO) can contribute either a B or an O allele. Therefore, their children could have AB, BB, AO, or BO blood types.

Question 9

In fruit flies, red-eyes are dominant to white-eyes. In addition, eye color is a sex-linked trait. A red-eyed male Drosophila mates with a red-eyed female Drosophila. One of the female's parents had white eyes. What proportion of the male offspring will have white eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Since eye color is a sex-linked trait located on the X chromosome and the female has a red eye but one parent with white eyes, she must be heterozygous (X^RX^w). The male, having red eyes and only one X chromosome, has the genotype X^RY. When they mate, half of the male offspring will inherit the X^w from the mother and the Y from the father, resulting in white eyes. Therefore, 50% of the male offspring will have white eyes.

Question 10

Linked genes
A) always assort independently.
B) undergo crossing-over of sister chromatids at a high rate.
C) are found on homologous chromosomes.
D) never cross over during prophase I.
E) tend to be close together on the same chromosome.

Accepted Answer

Linked genes are typically close together on the same chromosome, which means they tend to be inherited together more often than genes that are located far apart. This proximity reduces the likelihood of recombination between them during meiosis.

Question 11

Which of the following is true in regards to an autosomal recessive pedigree?
A) Heterozygotes have a normal phenotype.
B) Affected children will have at least one affected parent.
C) Heterozygotes are affected.
D) Males are affected more often than females.
E) The trait is carried on the Y chromosome.

Accepted Answer

Heterozygotes in an autosomal recessive pedigree carry one copy of the mutated gene and one copy of the normal gene, but they typically do not show symptoms of the disorder, displaying a normal phenotype instead.

Question 12

A male is always homozygous for a trait that is
A) codominant.
B) X-linked.
C) autosomal.
D) dominant.
E) dihybrid.

Accepted Answer

A male is always homozygous for X-linked traits because males have only one X chromosome. Any gene located on the X chromosome will be expressed in males, whether it is recessive or dominant, because there is no corresponding allele on the Y chromosome to potentially mask its expression.

Question 13

Unattached earlobes (EE or Ee) are dominant over attached earlobes (ee). A couple both have unattached earlobes but each one has a parent with attached earlobes (ee). Therefore, they correctly assume that they are carriers for attached earlobes (Ee). If the couple proceeds to have four children, then
A) they can be certain that three will be heterozygous and one homozygous recessive.
B) if the first three are heterozygous, the fourth must be homozygous recessive.
C) the children must repeat the grandparents' genotype (Ee).
D) all children must have unattached earlobes since both parents possess the dominant gene for it.
E) two heterozygous, one homozygous dominant, and one homozygous recessive is a likely outcome, but all heterozygous, or two, three, or all four homozygous is also possible.

Accepted Answer

The couple are both heterozygous (Ee), so each child has a 25% chance of being homozygous dominant (EE), a 50% chance of being heterozygous (Ee), and a 25% chance of being homozygous recessive (ee). Therefore, various combinations of genotypes are possible among the four children.

Question 14

Hydrangeas are a flowering plant with large showy blooms. When a plant is grown in acidic soil, it has blue flowers; if the same plant is transplanted into soil that is alkaline, the flowers produced will be pink. This is an example of
A) environmental influence.
B) codominance.
C) incomplete dominance.
D) polygenetic inheritance.
E) monohybrid inheritance.

Accepted Answer

The color change in hydrangea flowers from blue to pink depending on the soil pH is an example of environmental influence on the phenotype of the plant. The soil's acidity or alkalinity affects the availability of aluminum ions, which in turn affects the color of the flowers. This is not a genetic change but an environmental effect on the expression of genes.

Question 15

Traits that are controlled by several sets or pairs of alleles, such as skin color and height in humans, are the result of what form of inheritance?
A) polygenic
B) incomplete dominance
C) multiple allele systems
D) simple Mendelian inheritance
E) codominance

Accepted Answer

Traits that are controlled by several sets or pairs of alleles are the result of polygenic inheritance, where multiple genes contribute to the overall expression of the trait. This differs from multiple allele systems, which refer to genes that have more than two possible alleles, and incomplete dominance and codominance, which refer to how alleles interact with each other. Simple Mendelian inheritance refers to traits that are controlled by one set or pair of alleles.

Question 16

Which of the following is a true statement?
A) Females can be heterozygous for sex-linked traits.
B) All traits on the sex chromosomes are associated with sexual development.
C) Males inherit two copies of the SRY gene.
D) The X and Y chromosomes are homologous.
E) Men pass their X-linked traits to their sons.

Accepted Answer

Females have two X chromosomes, allowing them to be heterozygous for traits that are linked to the X chromosome. This means they can carry two different alleles for a trait, one on each of their X chromosomes.

Question 17

What genetic disorder is associated with the lack of an enzyme necessary for the normal metabolism of the amino acid phenylalanine?
A) phenylketonuria (PKU)
B) Marfan syndrome
C) Huntington disease
D) sickle-cell disease
E) cystic fibrosis (CF)

Accepted Answer

The genetic disorder associated with the lack of an enzyme necessary for the normal metabolism of the amino acid phenylalanine is phenylketonuria (PKU). This disorder is caused by mutations in the PAH gene, which codes for the enzyme phenylalanine hydroxylase. Without this enzyme, phenylalanine and its byproducts build up in the body, leading to intellectual disability and other health problems if left untreated.

Question 18

Hunter syndrome is a rare genetic disorder in which large sugar molecules called glycosaminoglycans build up in body tissues. Hunter syndrome causes abnormalities in many organs, including the skeleton, heart, and respiratory system. In severe cases, this leads to death during the teenage years. Hunter syndrome is caused by a recessive gene on the X chromosome. If a woman who is normal (but had a father with the disease) marries a normal man, what are the chances of having a daughter affected by the disease?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Hunter syndrome is an X-linked recessive disorder, meaning it is carried on the X chromosome. Since females have two X chromosomes, a daughter would need two copies of the affected gene to show symptoms of the disease. In this scenario, the mother is a carrier (her father had the disease, so she must have one affected X chromosome), but the father can only pass on a Y chromosome to daughters, making it impossible for a daughter to inherit the affected X chromosome from him. Therefore, daughters cannot be affected by the disease in this genetic cross.

Question 19

On one chromosome, the allele for white eyes is located at loci 12 and the allele for a hairy body is located at loci 16. On a second chromosome, the allele for red eyes is located at loci 15 and the allele for a normal body is located at loci 17. Which allele combination has the greater map distance?
A) white eyes and hairy body
B) white eyes and normal body
C) red eyes and normal body
D) red eyes and hairy body
E) white eyes and red eyes

Accepted Answer

The map distance between alleles is determined by the physical distance between their loci on a chromosome. For white eyes (loci 12) and a hairy body (loci 16), the distance is 4 loci, which is greater than the distances between any other given pair of alleles.

Question 20

Which of the following is a sex-linked recessive disorder?
A) color blindness
B) Marfan syndrome
C) sickle-cell disease
D) cystic fibrosis
E) alkaptonuria

Accepted Answer

Color blindness is a sex-linked recessive disorder, meaning it is often carried on the X chromosome. Since males have only one X chromosome, they are more frequently affected by this condition.

Quiz 10: Patterns of Inheritance

Which genetic disorder is associated with an irregular shape of the red blood cells?

Both parents are heterozygous for Tay-Sachs disease (an autosomal recessive disorder) . Three children in a row were born with Tay-Sachs disease. What is the chance that a fourth child will have Tay-Sachs disease?

In fruit flies, red-eyes are dominant to white-eyes. In addition, eye color is a sex-linked trait. If a homozygous red-eyed female Drosophila mates with a red-eyed male Drosophila. What proportion of the female offspring will have white eyes?

Which of the following is an autosomal dominant disorder?

A blue-eyed, left-handed woman marries a brown-eyed, right-handed man who is heterozygous for both of histraits. If blue eyes and left-handedness are recessive, how many different phenotypes are possible in their children?

Red-green color blindness is a recessive X-linked trait. If a female is red-green color-blind, which of the following is true?

A woman with type AB blood marries a man who is heterozygous for type B blood. If they have children, what are all the possible blood types for the children?

In fruit flies, red-eyes are dominant to white-eyes. In addition, eye color is a sex-linked trait. A red-eyed male Drosophila mates with a red-eyed female Drosophila. One of the female's parents had white eyes. What proportion of the male offspring will have white eyes?

Linked genes

Which of the following is true in regards to an autosomal recessive pedigree?

A male is always homozygous for a trait that is

Hydrangeas are a flowering plant with large showy blooms. When a plant is grown in acidic soil, it has blue flowers; if the same plant is transplanted into soil that is alkaline, the flowers produced will be pink. This is an example of

Traits that are controlled by several sets or pairs of alleles, such as skin color and height in humans, are the result of what form of inheritance?

Which of the following is a true statement?

What genetic disorder is associated with the lack of an enzyme necessary for the normal metabolism of the amino acid phenylalanine?

Which of the following is a sex-linked recessive disorder?