Question 1

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 disease is a dominant neurological disorder that leads to progressive degeneration of neurons in the brain.

Question 2

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

If the female is homozygous dominant, all of her daughters will have the dominant traits, so they will also have red eyes.

Question 3

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

A woman who is color-blind must have received one recessive allele from both her parents. Because her mother has two copies of the gene, she could be either color-blind or a carrier. However, her father only has one copy, so he must exhibit red-green color blindness.

Question 4

Vitamin-D resistant rickets is a sex-linked dominant trait, which leads to softening of the bones, which can cause fractures and deformities. Rickets is often due to a deficiency of vitamin D; however, with vitamin- D resistant rickets, ingestion of vitamin D is ineffective. Maria's mother is normal and does not display any symptoms of this disease. Maria's father, however, has the disease. Maria marries a man that does not have the disease. What is the probability that they will have a son that has the disease?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Maria must be heterozygous for the trait because her mother did not have the disease. Thus, there is a 50% chance that any of her sons will have the disease.

Question 5

Which is not true according to Mendel's law and meiosis?
A) One factor must be dominant and one factor recessive in each individual.
B) Each individual contains two factors for each trait.
C) Factors separate from each other during gamete formation.
D) Each gamete contains one copy of each factor.
E) Fertilization restores the presence of two factors.

Accepted Answer

While one allele may be dominant over another, it is not necessary for the individual to contain one of each choice. The individual could have two dominant alleles homozygous dominant) or two recessive alleles homozygous recessive).

Question 6

A woman with type AB blood marries a man with 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 man could be I^Bi or I^BI^B. Thus, any of these are possible.

Question 7

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

Polygenic inheritance would mean that there were multiple genes at different locations and possibly on different chromosomes all controlling one trait. Simple Mendelian genetics would indicate a simple dominant/ recessive relationship, whereas codominance would be a system where alleles both show in the offspring. Incomplete dominance would be a case where heterozygotes would show a different phenotype than either of the homozygotes.

Question 8

A blue-eyed, left-handed woman marries a brown-eyed, right-handed man who is heterozygous for both of his traits. 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

If B = brown eyes and b = blue eyes, and R = right-handed while r = left-handed, then the mother's genotype is bbrr and the father is BbRr. For a cross between an individual that is homozygous recessive for two traits and an individual that is heterozygous for those two traits, there would be a ratio of one dominant for both traits to one dominant for the first trait and recessive for the second to one recessive for the first trait and dominant for the second to one recessive for both traits, yielding four different phenotypes.

Question 9

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

The female must be heterozygous for the trait. Thus, there is a 50% chance that she will pass this trait on to any of her male children.

Question 10

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

Accepted Answer

X-linked refers to genes carried on the X chromosome. Males will only have one X chromosome so they are always considered homozygous.

Question 11

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 a single chromosome.

Accepted Answer

Linked genes are on the same chromosome and tend to be passed together.

Question 12

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 of any one child possessing a particular phenotype does not depend on the genotype of any sibling. The parents still have the same genotype, and the eggs and sperm are created from germ cells which contain both allele choices that the parents have. Therefore, the probability is the same for each child to have any one particular genotype. With two heterozygotes, this would mean a 75% chance of a normal phenotype and a 25% chance of a recessive phenotype.

Question 13

Which of the following is true?
A) Females can be heterozygous for sex-linked traits.
B) All traits on the sex chromosomes are associated with sexual development.
C) Males are heterozygous for 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 so THEY can be heterozygous. Males have only one copy of the X chromosome so they cannot be heterozygous for an X-linked trait.

Question 14

Unattached earlobes EE or Ee) are dominant over attached earlobes ee). A couple both have unattached earlobes. Both notice that one of their parents on both sides have 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 chance of any one child possessing a particular phenotype does not depend on the genotype of any sibling. The parents still have the same genotype, and the eggs and sperm are created from germ cells which contain both allele choices that the parents have. Therefore, the probability is the same for each child to have any one particular genotype. In this case, the probabilities would be 75% chance of unattached earlobes and a 25% chance of attached earlobes.

Question 15

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

Phenylketonuria PKU) is associated with the lack of the enzyme necessary for the metabolism of phenylalanine. Marfan syndrome is associated with a defect in the elastic connective tissue protein called fibrillin. Huntington disease is caused by a mutation to the protein huntingtin. Sickle-cell disease is an irregular shape of the red blood cells. Cystic fibrosis CF) is associated with a faulty protein channel in the cell membrane.

Question 16

Vitamin-D resistant rickets is a sex-linked dominant trait, which leads to softening of the bones, which can cause fractures and deformities. Rickets is often due to a deficiency of vitamin D; however, with vitamin- D resistant rickets, ingestion of vitamin D is ineffective. Maria's mother is normal and does not display any symptoms of this disease. Maria's father, however, has the disease. Maria marries a man that does not have the disease. What is the probability that they will have a daughter that has the disease?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Accepted Answer

Maria must be heterozygous for the trait because her mother did not have the disease. Thus, there is a 50% chance that any of her daughters will have the disease because only one copy of the gene is required.

Question 17

Amy has wavy hair and 6 fingers an autosomal dominant trait). Wavy hair is inherited through incomplete dominance. Which of the following combinations are possible for her parents? 
A) 5 only
B) 1 and 2
C) 1, 3, and 4
D) 2, 4, and 5
E) 2 and 4

Accepted Answer

At least one parent must have six fingers. Wavy hair is an intermediate trait so must have two different alleles.

Question 18

Ryan has type A blood and is color-blind an X-linked recessive trait). Which of the following combinations are possible for his parents? 
A) 1, 2, and 3
B) 1 and 2
C) 1, 3, and 4
D) 1, 2, 3, 4, and 5
E) 1, 3, 4, and 5

Accepted Answer

If the mother has normal vision, she could still be a carrier for the color-blind trait. The son inherits this trait from his mother, so it does not matter whether his father is color-blind or not; it will not affect the son. Ryan could have either AO or AA blood, so many of the blood type combinations expect both parents type B) are possible.

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 units between white eyes and hairy body is four units, while the map units between red eyes and a normal body is two units. The alleles have to be on the same chromosome to measure the map units.

Question 20

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 an irregular shape of the red blood cells. Marfan syndrome is associated with a defect in the elastic connective tissue protein called fibrillin. Huntington disease is caused by a mutation to the protein huntingtin. Phenylketonuria PKU) is associated with the lack of the enzyme necessary for the metabolism of phenylalanine. Cystic fibrosis CF) is associated with a faulty protein channel in the cell membrane.

Quiz 10: Patterns of Inheritance

Which of the following is an autosomal dominant disorder?

A homozygous red-eyed female Drosophila mates with a red-eyed male Drosophila. What proportion of the female offspring will have white eyes?

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

Which is not true according to Mendel's law and meiosis?

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

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

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 male is always homozygous for a trait that is

Linked genes

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?

Which of the following is true?

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

Amy has wavy hair and 6 fingers an autosomal dominant trait) . Wavy hair is inherited through incomplete dominance. Which of the following combinations are possible for her parents?

Ryan has type A blood and is color-blind an X-linked recessive trait) . Which of the following combinations are possible for his parents?

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