Question 1

A trait such as albinism is seen with equal frequency in males and females. Two people who do not have the trait might have offspring who do have the trait, at a frequency of approximately one in four. What can you conclude about the inheritance of this trait?

Accepted Answer

The fact that the trait is seen with equal frequency in males and females suggests that it is not X-linked. The fact that two unaffected parents can have affected offspring at a frequency of approximately one in four suggests that the trait is recessive rather than dominant. Therefore, the inheritance pattern of this trait is likely to be recessive and autosomal.

Question 2

What is a recessive disorder?

Accepted Answer

A recessive disorder is a genetic disorder that will express itself only in the presence of two recessive alleles. This means that an individual must inherit two copies of the defective gene, one from each parent, to develop the disorder. If a person inherits only one defective allele, they are said to be a carrier of the disorder but will not develop symptoms.

Question 3

A person with an inherited disorder has children with a person who does not have the condition. Half the children have the disorder, both sons and daughters. How is this condition inherited?

Accepted Answer

The pattern described indicates an autosomal dominant inheritance because the disorder is present in both sons and daughters (indicating it's not sex-linked) and it's passed from a single parent, which is characteristic of dominant inheritance patterns.

Question 4

Genes not found on the sex chromosomes will be found on:

Accepted Answer

Autosomes are the chromosomes that are not sex chromosomes (X and Y). These chromosomes contain most of an individual's genetic information and are found in both males and females.

Question 5

If a disease is caused by a dominant allele, it means that a person with the disease:

Accepted Answer

If a disease is caused by a dominant allele, a person with the disease could have one copy of the allele (heterozygous) or two copies (homozygous dominant). Both scenarios would result in the expression of the disease, as only one copy of a dominant allele is needed for its phenotype to be expressed.

Question 6

What is the connection between sickle-cell anemia and malaria?

Accepted Answer

Heterozygotes for sickle-cell anemia have a higher resistance to malaria due to the fact that sickle cell trait causes red blood cells to be less hospitable to the malaria parasite. This is why sickle-cell anemia is more prevalent in areas where malaria is common.

Question 7

Red-green color blindness is an X-linked recessive trait in humans. A color-blind woman and a man with normal vision have a son. What is the probability that the son is color blind?

Accepted Answer

The answer of Red-green color blindness is an X-linked recessive...

Question 8

What do hemophilia, Duchenne muscular dystrophy, and red-green color blindness have in common?

Accepted Answer

Hemophilia, Duchenne muscular dystrophy, and red-green color blindness are all X-linked disorders, which means the genes responsible for these disorders are located on the X chromosome. As females have two X chromosomes, they can carry a mutated gene and still have a normal copy on the other X chromosome, while males only have one X chromosome, and if it carries a mutated gene, they will develop the disorder.

Question 9

What percent of males have some degree of color blindness?

Accepted Answer

According to the National Eye Institute, approximately 8 percent of males have some degree of color blindness.

Question 10

A woman who is a carrier for the hemophilia gene has a child with a man who does not have hemophilia. Which prediction is correct?

Accepted Answer

Hemophilia is an X-linked recessive disorder. Females have two X chromosomes, while males only have one X chromosome and one Y chromosome. If a female is a carrier for hemophilia, she has one X chromosome with the normal allele and one X chromosome with the mutant allele. When she has a child with a male who does not have hemophilia, there are several possibilities.

Each child has a 50% chance of inheriting the X chromosome with the mutant allele and a 50% chance of inheriting the X chromosome with the normal allele. 
- Daughters: If a daughter inherits only the normal allele, she will not have hemophilia. If a daughter inherits the mutant allele, she will be a carrier like her mother. Therefore, half of the daughters will be carriers for hemophilia.
- Sons: If a son inherits the normal allele, he will not have hemophilia. However, if a son inherits the mutant allele, he will have hemophilia because there is no second X chromosome to compensate for the defective one. Therefore, half of the sons will have hemophilia.

Therefore, the correct prediction is that half of the sons and none of the daughters will have hemophilia. Choice D is the correct answer.

Question 11

An autosomal recessive disorder:

Accepted Answer

An autosomal recessive disorder requires that both parents carry a copy of the mutated gene for it to appear in their children. Therefore, it will appear only in children of parents who both carry the gene.

Question 12

Regarding the human sex chromosomes, which statement is correct?

Accepted Answer

The X chromosome carries more genes than does the Y chromosome. In humans, the X chromosome carries over 1,000 genes, while the Y chromosome carries only about 50-60 genes.

Question 13

If a daughter expresses an X-linked recessive gene, she probably inherited the trait from:

Accepted Answer

For a daughter to express an X-linked recessive trait, she must inherit one copy of the recessive gene from each parent, as females have two X chromosomes (one from each parent).

Question 14

Color blindness is caused by an X-linked recessive gene. A color-blind man and a woman with normal vision whose father was color blind have a son. The probability that their son is color blind is:

Accepted Answer

Since color blindness is X-linked recessive, the son can only inherit the X-linked gene from his mother (since he gets a Y chromosome from his father). Therefore, if his mother is a carrier for the color blindness gene (since her father was color blind), there is a 50% chance that she will pass on the gene to her son. This means there is a 50% chance that their son will be color blind.

Question 15

A person who has a recessive disorder but does not have the disorder him or herself is said to be a/an:

Accepted Answer

A carrier is a person who has one normal gene and one mutated gene for a recessive disorder. While they do not exhibit symptoms of the disorder, they can potentially pass the mutated gene on to their offspring. Aneuploid refers to having an abnormal number of chromosomes, aberration refers to a deviation from what is normal or expected, and hybrid usually refers to the offspring of two different species or varieties.

Question 16

Why do X-linked conditions appear more frequently in males than in females?

Accepted Answer

Males only have one X chromosome, so if they inherit a nonfunctioning allele on that chromosome, they have no backup copy to compensate. Females, on the other hand, have two X chromosomes, so if one X chromosome has a nonfunctioning allele, the other X chromosome can often compensate.

Question 17

A woman who does not carry the color-blindness allele has children with a man who is color blind. What proportion of their children will be color blind?

Accepted Answer

Color blindness is typically inherited in an X-linked recessive manner. Since the woman does not carry the allele for color blindness, all her children will inherit a normal X chromosome from her. The sons will inherit their Y chromosome from their father and thus cannot be color blind, while the daughters will inherit an unaffected X chromosome from their mother and a color-blind X from their father, making them carriers but not color blind themselves.

Question 18

A person who is heterozygous for the Huntington disease (HD) allele has offspring with someone who does not have HD. What proportion of their children will have HD?

Accepted Answer

Huntington's disease (HD) is an autosomal dominant disorder, meaning that only one copy of the defective gene (heterozygous condition) is sufficient for an individual to be affected. If one parent is heterozygous for HD and the other parent does not have the HD allele, each child has a 50% (1/2) chance of inheriting the HD allele and thus the condition.

Question 19

Who is a "carrier" of X-linked disorders, such as hemophilia and color blindness?

Accepted Answer

A carrier of an X-linked disorder is typically a heterozygous female who carries one nonfunctioning allele on one X chromosome and one functioning allele on the other X chromosome. This means that she does not exhibit the disorder herself, but can pass the nonfunctioning allele on to her offspring.

Question 20

What condition is caused by a dominant allele of a single gene?

Accepted Answer

Huntington disease is caused by a dominant allele of a single gene on chromosome 4. The presence of one copy of the mutated gene is enough to cause the disease.

Quiz 12: Units of Heredity: Chromosomes and Inheritance