Question 1

Which disorder is characterized by a lack of the protein dystrophin?

Accepted Answer

Muscular dystrophy is characterized by a lack of the protein dystrophin, which is necessary for maintaining the structure and function of muscle fibers. Hemophilia is caused by a deficiency in blood clotting factors, color-blindness is caused by a genetic mutation affecting cone cells in the eye, Down syndrome is caused by an extra copy of chromosome 21, and cystic fibrosis is caused by a mutation affecting the CFTR gene, which is responsible for regulating the transport of salt and water in and out of cells.

Question 2

Which refers to the addition of a repeat segment of a chromosome?

Accepted Answer

Duplication refers to the addition of a repeat segment of a chromosome. This results in an extra copy of a segment within the chromosome. In contrast to deletion, which involves the loss of a segment of a chromosome, duplication involves the gain of genetic material.

Question 3

The chances of survival are greater when trisomy or monosomy involves the sex chromosomes.

Accepted Answer

This is because humans can often tolerate the loss or gain of a sex chromosome without severe consequences, unlike trisomy or monosomy involving autosomes.

Question 4

Which of the following conditions is due to a sex-linked gene?

Accepted Answer

All of the listed conditions are caused by sex-linked genes located on the X chromosome. Color-blindness, hemophilia, and muscular dystrophy are recessive traits that affect mostly males, who have only one X chromosome. Inability to see red or green is a type of color-blindness and is also an X-linked recessive trait. Therefore, all of the answer choices are sex-linked conditions.

Question 5

An individual who has an XXY combination of sex chromosomes is said to have

Accepted Answer

An XXY combination of sex chromosomes is a characteristic of Klinefelter syndrome.

Question 6

If an individual has a XYY genotype, they are classified as having

Accepted Answer

Individuals with a XYY genotype have Jacobs syndrome, which occurs when a male has an extra Y chromosome. This condition does not typically result in severe physical or intellectual disabilities, but may lead to taller stature and higher risk of certain behavioral and learning difficulties. Down syndrome, cri du chat syndrome, Turner syndrome, and Klinefelter syndrome all result from different chromosomal abnormalities.

Question 7

In fruit flies, bar eye is inherited by a dominant X-linked allele (B for bar). If a heterozygous bar-eyed female is mated to a non-bar-eyed male, what will be the expected ratio of phenotype given four offspring?

Accepted Answer

The heterozygous bar-eyed female would have one X chromosome with the dominant B allele and one X chromosome with the non-bar-eyed allele. The non-bar-eyed male would only have non-bar-eyed alleles. The expected ratio of phenotypes would be one bar-eyed female (with the dominant B allele on her X chromosome), one non-bar-eyed female (with the non-bar-eyed allele on her X chromosome), one bar-eyed male (with the dominant B allele on his X chromosome), and one non-bar-eyed male (with the non-bar-eyed allele on his X chromosome). Therefore, choice B matches this expected ratio.

Question 8

An XXX female would most likely result from nondisjunction in

Accepted Answer

Nondisjunction occurs when chromosomes fail to separate during meiosis, resulting in gametes with an abnormal number of chromosomes. In this case, an XXX female would result from the failure of the X chromosome to separate from one of the pairs during meiosis in the mother's egg cell. Therefore, the most likely scenario for nondisjunction resulting in an XXX female is during egg formation in the mother.

Question 9

Generally, it is not possible to determine whether nondisjunction failed to occur in oogenesis or spermatogenesis. However, it is possible to assert that XYY results from nondisjunction during

Accepted Answer

XYY syndrome is the result of nondisjunction during spermatogenesis, specifically when an extra copy of the Y chromosome fails to separate from the other copy during cell division in the father's testes.

Question 10

Considering that males can have Klinefelter (XXY) syndrome, XYY, and normal XY chromosomal combinations, and females can have Turner (XO) syndrome, poly-X (XXX, XXXX), and normal XX combinations, it is obvious that

Accepted Answer

Male characteristics result from the presence of the minimal amount of one Y chromosome. The Y chromosome contains the key gene SRY, which triggers the development of male gonads (testes) in the early stages of embryonic development. The X chromosome does not determine maleness, but rather contributes to other traits such as height, hair color, and immune function. Therefore, males can have a variety of chromosomal combinations as long as they have at least one Y chromosome to trigger male development.

Question 11

If a chromosomal segment is turned around 180°, the chromosomal mutation is termed a(n)

Accepted Answer

When a chromosomal segment is turned around 180°, it is undergoing an inversion. This is different from a translocation where a segment of one chromosome is moved to a different chromosome, a duplication where a segment is duplicated, a deletion where a segment is lost, or monosomy where there is only one copy of a chromosome instead of the normal two.

Question 12

If a person has a portion of number 5 chromosome missing, they may have

Accepted Answer

Cri du chat syndrome, also known as 5p- (5p minus) syndrome, is caused by a deletion of a portion of the short arm of chromosome 5. This results in developmental delays, intellectual disability, characteristic facial features, and a distinctive cry that sounds like a cat's meow. Down syndrome, Turner syndrome, Klinefelter syndrome, and Jacobs syndrome are all caused by different chromosomal abnormalities.

Question 13

Which of the following refers to the movement of a piece of one chromosome to another nonhomologous chromosome?

Accepted Answer

Translocation specifically refers to the movement of a piece of one chromosome to another nonhomologous chromosome. Inversion refers to the reversal of a segment of a chromosome, deletion refers to the loss of a segment of a chromosome, duplication refers to the repetition of a segment of a chromosome, and monosomy refers to when a cell is missing one copy of a chromosome.

Question 14

A person with an XO genotype is classified as having

Accepted Answer

An XO genotype typically refers to a person who has only one X chromosome, which is characteristic of Turner syndrome. Down syndrome is caused by an extra copy of chromosome 21, cri du chat syndrome is caused by a deletion on the short arm of chromosome 5, Klinefelter syndrome is characterized by an extra X chromosome in males (XXY), and a poly-X state refers to a person who has extra X chromosomes but is not necessarily limited to only having one X chromosome as in the case of XO.

Question 15

If a person inherits two X chromosomes, this individual will be

Accepted Answer

Inheriting two X chromosomes results in the individual being female.

Question 16

A female that has ovarian failure and does not undergo puberty may have

Accepted Answer

Turner syndrome is a genetic disorder that affects females and is caused by abnormalities in one of the two sex chromosomes. These individuals typically have a missing or partially missing X chromosome, leading to ovarian failure and lack of puberty.

Question 17

If a woman is a carrier for the color-blind recessive allele and her husband has normal vision, what are their chances that a son will be color-blind?

Accepted Answer

Color blindness is an X-linked recessive trait. Since the mother is a carrier (XcX), she has one normal allele (X) and one color-blind allele (c). The father, with normal vision, has only the normal allele (XY). A son inherits the Y chromosome from his father and one of the X chromosomes from his mother. If he inherits the X chromosome carrying the color-blind allele (c) from his mother, he will be color-blind. This gives a 50% chance, as the son could inherit either the mother's normal X or her color-blind X.

Question 18

The trait diagrammed in Figure 24.4 is inherited as a(n)

Accepted Answer

The trait is only expressed in males, indicating that it is on the X chromosome, and it skips generations, indicating that it is recessive. Therefore, the trait is a recessive X-linked trait.

Question 19

Which of the following refers to the loss of a portion of a chromosome?

Accepted Answer

Deletion refers to the loss of a portion of a chromosome, which can result in genetic disorders or abnormalities. Inversion, translocation, duplication, and monosomy all involve changes to the chromosome structure or number, but do not necessarily entail the loss of genetic material.

Question 20

Which of the following is true about a karyotype?

Accepted Answer

All of the answer choices are true about karyotypes. Homologous chromosomes are arranged in pairs, sex chromosomes are identified separately from autosomes, chromosome pairs are assorted by both size and shape, and banding patterns are used in pairing chromosomes.

Quiz 24: Chromosomal Basis of Inheritance