Question 1

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

Since red-green color blindness is an X-linked recessive trait, a color-blind woman must have two copies of the allele (one on each of her X chromosomes) to express the trait. A man with normal vision has a normal X chromosome. Their son inherits one X chromosome from his mother (which carries the color-blind allele) and a Y chromosome from his father, making him color blind.

Question 2

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 3

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 the mother has normal vision, she must be heterozygous for the color-blindness gene (meaning she carries one normal X chromosome and one X chromosome with the color-blindness gene). The father, being color-blind, must have two copies of the color-blindness gene, one on each X chromosome.

Therefore, the mother has a 50% chance of passing on the normal X chromosome to her son, which would result in him having normal vision. Alternatively, she has a 50% chance of passing on the X chromosome with the color-blindness gene to her son, which would result in him being color-blind.

Since these two possibilities are equally likely, the probability that their son is color-blind is 0.50 (or 50%).

Question 4

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

Accepted Answer

Heterozygotes for sickle-cell anemia have some resistance to malaria. The sickle-cell gene is found in areas where malaria is prevalent, suggesting that it offers some protection against the disease. This is because the parasite that causes malaria cannot survive as well in the red blood cells of those who have the sickle-cell trait. As a result, individuals who carry one copy of the sickle-cell gene are less likely to get sick from malaria.

Question 5

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 two people without the trait can have offspring with the trait at a frequency of approximately one in four suggests that the trait is recessive. The equal frequency in males and females suggests that it is autosomal rather than X-linked or Y-linked. The trait is not caused by polyploidy as that refers to having extra sets of chromosomes. The fact that the trait appears in the offspring suggests that it is heritable and not a new mutation, ruling out dominant inheritance. Therefore, the best choice is B- recessive, autosomal inheritance.

Question 6

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 7

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 8

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 X chromosome, they do not have a backup copy on another X chromosome like females do. This makes them more susceptible to X-linked conditions.

Question 9

An autosomal recessive disorder:

Accepted Answer

An autosomal recessive disorder requires both parents to carry the gene for the disorder in order for it to appear in their children. If only one parent is a carrier, their children will not have the disorder but may be carriers themselves. The disorder is not limited to heterozygotes, as homozygotes for the recessive gene will also display the disorder. The frequency in males and females is not necessarily different, as it depends on the specific disorder. It is also not dominant in females, as dominance does not depend on gender.

Question 10

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 someone who carries a recessive gene for a genetic disorder but does not have the disorder themselves. This means they can transmit the gene to their offspring and, if their partner also carries the gene or has the disorder, their child may develop the disorder. Aneuploid refers to an abnormal number of chromosomes, aberration refers to a genetic error or deviation from the normal pattern, and hybrid refers to the offspring of two different species or breeds.

Question 11

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

Accepted Answer

Genes that are not found on the sex chromosomes are referred to as autosomal genes. These genes are found on the other 22 pairs of chromosomes that are not involved in determining an individual's sex.

Question 12

What is a recessive disorder?

Accepted Answer

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

Question 13

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.

Question 14

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 that the genes responsible for these conditions are located on the X chromosome. As a result, these conditions are more common in males, who only have one X chromosome, and are typically inherited from carrier females.

Question 15

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

Accepted Answer

X-linked disorders are caused by mutations on the X chromosome. Since females have two X chromosomes, they can be carriers of X-linked disorders if they inherit a nonfunctioning allele on one of their X chromosomes, but not on the other. Heterozygous females who inherit one normal and one nonfunctioning allele are carriers but do not express the disorder. Therefore, option B is the correct choice. The other options are incorrect because carriers do not have the disorder, and males only have one copy of the X chromosome, making them more susceptible to X-linked disorders.

Question 16

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 17

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

The hemophilia gene is carried on the X chromosome, and since women have two X chromosomes, if one of the X chromosomes carries the hemophilia gene, the other X chromosome can compensate for it. Therefore, carriers of the hemophilia gene usually do not have hemophilia. On the other hand, men have only one X chromosome, so if it carries the hemophilia gene, they will have hemophilia. In this case, since the mother is a carrier and the father does not have hemophilia, there is a 50% chance that each son will inherit the hemophilia gene and, therefore, have hemophilia. Since daughters inherit one X chromosome from each parent, there is also a 50% chance that each daughter will inherit the hemophilia gene. However, since carriers of the gene do not typically have the disease, the daughters who inherit the hemophilia gene will be carriers like their mother, rather than having the disease themselves. Therefore, the correct prediction is that half of the sons and none of the daughters will have hemophilia.

Question 18

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 19

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 20

Regarding the human sex chromosomes,which statement is correct?

Accepted Answer

The X chromosome carries more genes than the Y chromosome. The X chromosome contains over 1,000 genes, while the Y chromosome contains only about 78 genes.

Quiz 12: Units of Heredity: Chromosomes and Inheritance