Question 1

The genetic disease blue sclera is determined by an autosomal dominant allele.The eyes of individuals with this allele have bluish sclera.These same individuals may also suffer from fragile bones and deafness.This is an example of
A) incomplete dominance.
B) linkage.
C) epistasis.
D) codominance.
E) pleiotropy.

Accepted Answer

This is an example of pleiotropy because a single allele affects multiple traits: bluish sclera, fragile bones, and deafness.

Question 2

One true-breeding line of mice is obese and dark, and the other true-breeding line is lean and light.Dark is dominant to light, but obese and lean exhibit incomplete dominance.The two genes involved are on separate chromosomes.What proportion of offspring from a dihybrid cross should be dark and obese?
A) 1/16
B) 3/16
C) 1/4
D) 3/8
E) 9/16

Accepted Answer

The answer of One true-breeding line of mice is obese...

Question 3

Suppose a woman has blood type AB.From this, we can infer that
A) her mother was also blood type AB.
B) her father was also blood type AB.
C) her father was type A, and her mother was type B.
D) her mother was type A, and her father was type B.
E) neither of her parents was type O.

Accepted Answer

Blood type AB can be inherited only if at least one parent has an A allele and the other has a B allele. Since type O lacks both A and B alleles, neither parent can have type O.

Question 4

A population of Drosophila simulans carries three alleles at the white locus: the wild-type allele at 86 percent, w₁ at 9 percent, and w₂ at 5 percent.What can we say about this population? A) There must be other alleles that have not been sampled. B) The population is polymorphic. C) w₁ must be dominant to w₂. D) w₂ must be dominant to w₁. E) The white locus has pleiotropic effects.

Accepted Answer

The fact that there are three alleles present in the population indicates that it is polymorphic, meaning that there is more than one allele at the locus. Option A is not necessarily true, as it is possible that these are the only three alleles present in the population. The information given does not provide sufficient evidence to determine whether one allele is dominant to the other, so options C and D are not necessarily true. Option E is not supported by the information given.

Question 5

One true-breeding line of mice is obese and dark, and the other true-breeding line is lean and light.Dark is dominant to light, but obese and lean exhibit incomplete dominance.The two genes involved are on separate chromosomes.What proportion of offspring from a dihybrid cross should be dark and be intermediate between obese and lean?
A) 1/16
B) 3/16
C) 1/4
D) 3/8
E) 9/16

Accepted Answer

The dihybrid cross can be written as:

DDOO x ddoo

where D represents the dominant allele for dark color, d represents the recessive allele for light color, O represents the dominant allele for obese, and o represents the recessive allele for lean.

The gametes produced by the first parent are all DO, and the gametes produced by the second parent are all do. The possible genotypes and phenotypes of the offspring are:

DdOo (dark and intermediate) 	9/16
Ddoo (dark and lean) 		3/16
ddOo (light and intermediate) 	3/16
ddoo (light and lean) 		1/16

Therefore, the proportion of offspring that are dark and intermediate between obese and lean is 9/16, which corresponds to choice D.

Question 6

Suppose a man is blood type O.From this, we can infer that
A) at least one of his parents must be type O.
B) his daughters must be type O.
C) his sons must be type O.
D) none of his children can be type AB.
E) none of his children can be type B.

Accepted Answer

Blood type O is recessive, meaning both alleles in the person are O. While a child can inherit an O allele from this man and any allele from the other parent, they cannot inherit an A and a B allele together to form AB blood type, as this man can only pass on an O allele.

Question 7

In a plant, a single locus affects both berry color and berry size.There are two mutant alleles (R₁ and R₂) in addition to the wild-type allele (R₀).Individuals that are R₀R₀ have large, white berries.Individuals that are R₁R₁ or R₀R₁ have red berries, individuals that are R₂R₂ or R₀R₂ have small berries, and R₁R₂ individuals have berries that are both red and small.What are the expected phenotypic ratios if you crossed R₁R₂ individuals to homozygous wild type? A) All would have small white berries. B) All would have large red berries. C) Half would have small white berries, and half would have large red berries. D) One-third would have wild-type berries, one-third would have small white berries, and one-third would have large red berries. E) One-quarter would have wild-type berries, one-half would have small white berries, and one-quarter would have large red berries.

Accepted Answer

The phenotype of the heterozygous parental crosses are R₁R₂ x R₀R₀. The Punnett square for this cross would be: | R₁ | R₂ --|----------------|---------------- R₀ | RrSs | RrSs R₀ | RrSs | RrSs Therefore, the expected phenotypic ratio is 1:1 for large red (RRss and Rrss) and small white (rrSS and rrSs) berries, resulting in half the offspring having small white berries, and half the offspring having large red berries.

Question 8

Refer to the figure showing a family pedigree in which several individuals develop a neurodegenerative disease late in life.  If individual A (in generation III) has children with an unaffected woman, what is the probability that their first child will be affected?
A) 0 percent
B) 25 percent
C) 33 percent
D) 50 percent
E) 100 percent

Accepted Answer

The answer of Refer to the figure showing a family...

Question 9

Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait.  What is the probability an individual in generation IV will have the disease?
A) 0.03125
B) 0.0625
C) 0.125
D) 0.375
E) 0.5

Accepted Answer

In order for an individual in generation IV to have the disease, they must inherit the trait from both parents. Since the mother in generation III is a carrier of the trait, there is a 50% chance she will pass it on to each of her offspring. The father in generation III does not carry the trait, so none of his offspring will inherit the trait from him. Therefore, the probability of an individual in generation IV inheriting the trait from both parents is 0.5 x 0.5 = 0.25 (or 1/4). However, only half of the children of the carrier mother in generation III will be affected, so the final probability is 0.25 x 0.5 = 0.125 (or 1/8).

Question 10

What distinguishes the phenotypes of the different ABO groups?
A) Different proteins on the surfaces of red blood cells
B) Different proteins inside red blood cells
C) Different nucleic acids on the surfaces of red blood cells
D) Different oligosaccharides inside red blood cells
E) Different oligosaccharides on the surfaces of red blood cells

Accepted Answer

The ABO blood group system is determined by the presence or absence of certain oligosaccharides on the surfaces of red blood cells. Group A individuals have the A antigen, which is made up of the A oligosaccharide, group B individuals have the B antigen, which is made up of the B oligosaccharide, group AB individuals have both A and B antigens, and group O individuals have neither A nor B antigens. These differences in oligosaccharides on the surfaces of red blood cells are what distinguish the phenotypes of the different ABO groups.

Question 11

A certain species of fish has alleles for red scales and for blue scales.Mating a red-scaled fish to a blue-scaled fish yields fish with a patchwork of red and blue scales.Mating one of these patchwork fish to a blue-scaled fish yields half patchwork and half blue-scaled fish.What can you conclude about the red and blue alleles?
A) The blue allele is dominant.
B) The red allele is dominant.
C) The red and blue alleles show incomplete dominance.
D) The red and blue alleles are codominant.
E) The alleles are pleiotropic.

Accepted Answer

The fact that both red and blue alleles are expressed in the patchwork fish suggests that they are codominant. This means that when both alleles are present, they are both expressed equally in the phenotype. The half patchwork and half blue-scaled fish from the second mating also supports this idea, as it indicates that the patchwork allele and the blue allele have equal chances of being inherited. None of the other answer choices are supported by the information given.

Question 12

Which transfusion is most likely to cause an immune reaction?
A) A transfusion of O type blood to a person with A type blood
B) A transfusion of A type blood to a person with O type blood
C) A transfusion of B type blood to a person with AB type blood
D) A transfusion of O type blood to a person with O type blood
E) A transfusion of AB type blood to a person with AB type blood

Accepted Answer

A person with O type blood has both anti-A and anti-B antibodies in their blood, so if they receive a transfusion of A type blood (which contains A antigens), their antibodies will recognize the antigens as foreign and mount an immune response, potentially leading to a transfusion reaction. The other options either involve a person receiving their own blood type (D) or receiving a blood type that their body is already compatible with (A, C, E).

Question 13

Which statement about phenylketonuria is false?
A) It arises from a defective enzyme.
B) The allele that causes phenylketonuria has pleiotropic effects.
C) It can lead to mental retardation.
D) It can lead to skin disorders.
E) The allele that causes phenylketonuria has incomplete dominance.

Accepted Answer

The statement that the allele that causes phenylketonuria has incomplete dominance is false. PKU is an example of a recessively inherited disorder, meaning an individual must inherit two copies of the defective gene (one from each parent) to express the condition. The defective gene codes for an enzyme called phenylalanine hydroxylase, which is responsible for converting the amino acid phenylalanine to another amino acid called tyrosine. Without this enzyme, phenylalanine builds up in the body and can cause neurological damage, leading to mental retardation. Additionally, phenylalanine can be converted into other harmful compounds in the body, leading to skin disorders, among other symptoms.

Question 14

In the ABO blood type system,
A) A, B, and O are codominant.
B) A, B, and O are incompletely dominant.
C) A is dominant to B, and B is dominant to O.
D) O is incompletely dominant to A and B.
E) A and B are codominant.

Accepted Answer

In the ABO blood type system, A and B are codominant, meaning that if an individual inherits both the A and B alleles, both types of antigen will be expressed on the red blood cells. This is different from incomplete dominance, where a heterozygote exhibits a phenotype that is intermediate between the two homozygous phenotypes. O blood type is recessive to A and B, meaning that an individual must inherit two copies of the O allele to exhibit the O blood type phenotype.

Question 15

Which statement about pleiotropy is true?
A) It involves the expression of an allele.
B) It is observed only after dihybrid crosses.
C) It is observed only after test crosses.
D) It must involve several genes.
E) It is caused by incomplete dominance.

Accepted Answer

Pleiotropy involves a single gene affecting multiple traits, and therefore involves the expression of an allele.

Answer: D
 Pleiotropy can involve multiple traits controlled by a single gene, and therefore must involve several genes.

Answer: E
 Pleiotropy is not caused by incomplete dominance, which involves a blending of traits.

Question 16

Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait.  What is the probability that a member of generation III will be a carrier of this trait?
A) 0.1
B) 0.25
C) 0.5
D) 0.75
E) 1

Accepted Answer

The answer of Refer to the figure showing a family...

Question 17

Human geneticists assume that any allele that causes an abnormal phenotype is
A) dominant.
B) recessive.
C) pleiotropic.
D) rare.
E) common.

Accepted Answer

Human geneticists often assume that any allele causing an abnormal phenotype is rare because most populations have undergone natural selection that tends to eliminate or reduce the frequency of alleles that cause harmful or disadvantageous traits.

Question 18

In Mendel's experiments, if the allele for tall (T) plants was incompletely dominant over the allele for short (t) plants, what offspring would have resulted from crossing two Tt plants?
A) ¼ tall; ½ intermediate height; ¼ short
B) ½ tall; ¼ intermediate height; ¼ short
C) ¼ tall; ¼ intermediate height; ½ short
D) All tall offspring
E) All intermediate-height offspring

Accepted Answer

In incomplete dominance, the heterozygous phenotype (Tt) is a blend of the two homozygous phenotypes. Crossing two Tt plants would produce offspring with a 1:2:1 ratio of TT:Tt:tt, translating to ¼ tall (TT), ½ intermediate height (Tt), and ¼ short (tt).

Question 19

What do geneticists call stable inherited changes in genetic material?
A) Genes
B) Pedigrees
C) Mutations
D) Antigens
E) Wild-type alleles

Accepted Answer

Geneticists call stable inherited changes in genetic material mutations. Genes refer to specific stretches of DNA that contribute to a specific trait or function. Pedigrees are diagrams that show the inheritance pattern of a specific trait or disease within a family. Antigens are molecules that stimulate an immune response. Wild-type alleles are the most common form of a gene found in a population.

Question 20

In a plant, a single locus affects both berry color and berry size.There are two mutant alleles (R₁ and R₂) in addition to the wild-type allele (R₀).Individuals that are R₀R₀ have large, white berries.Individuals that are R₁R₁ or R₀R₁ have red berries, individuals that are R₂R₂ or R₀R₂ have small berries, and R₁R₂ individuals have berries that are both red and small.Thus, A) R₁ is dominant to R₂. B) R₂ is dominant to R₁. C) R₁ and R₂ exhibit incomplete dominance. D) R₁ and R₂ exhibit pleiotropy. E) R₁ and R₂ exhibit codominance.

Accepted Answer

The answer of In a plant, a single locus affects...

Quiz 12: Inheritance, Genes, and Chromosomes

The genetic disease blue sclera is determined by an autosomal dominant allele.The eyes of individuals with this allele have bluish sclera.These same individuals may also suffer from fragile bones and deafness.This is an example of

Suppose a woman has blood type AB.From this, we can infer that

A population of Drosophila simulans carries three alleles at the white locus: the wild-type allele at 86 percent, w1 at 9 percent, and w2 at 5 percent.What can we say about this population?

Suppose a man is blood type O.From this, we can infer that

Refer to the figure showing a family pedigree in which several individuals develop a neurodegenerative disease late in life. If individual A (in generation III) has children with an unaffected woman, what is the probability that their first child will be affected?

Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait. What is the probability an individual in generation IV will have the disease?

What distinguishes the phenotypes of the different ABO groups?

Which transfusion is most likely to cause an immune reaction?

Which statement about phenylketonuria is false?

In the ABO blood type system,

Which statement about pleiotropy is true?

Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait. What is the probability that a member of generation III will be a carrier of this trait?

Human geneticists assume that any allele that causes an abnormal phenotype is

In Mendel's experiments, if the allele for tall (T) plants was incompletely dominant over the allele for short (t) plants, what offspring would have resulted from crossing two Tt plants?

What do geneticists call stable inherited changes in genetic material?

A population of Drosophila simulans carries three alleles at the white locus: the wild-type allele at 86 percent, w₁ at 9 percent, and w₂ at 5 percent.What can we say about this population?