Chapter 15 Questions Flashcards Preview

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Flashcards in Chapter 15 Questions Deck (79)

The chromosome theory of inheritance states that _____.

-genes occupy specific positions on chromosomes
-homologous chromosomes segregate from each other during meiosis
-chromosomes assort independently during meiosis


Why did Morgan choose Drosophila for his genetics experiments?

-A single mating can produce many offspring.
-Drosophila chromosomes can be easily distinguishable under a light microscope.


Wild type refers to _____.

the most common phenotype thought to be found in the natural population


Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics?

Among the F2 progeny, only males had white eyes. All of the females had red eyes.


What is the probability that a male will inherit an X-linked recessive allele from his father?



In an X-linked, or sex-linked, trait, it is the contribution of _____ that determines whether a son will display the trait

the mother


If a mother is heterozygous for a recessive sex-linked trait and her husband has the dominant allele, which one of the following is true about the probabilities for their children?

Half of their sons will have the recessive trait.

-All the sons will receive Y chromosomes from their father. The X must come from the heterozygous mother; therefore, each son has a 50% chance of inheriting the recessive allele.


In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?


-The female werewolf must be heterozygous, because her father has round ears. Each of her sons has a 50% chance of inheriting the round allele.


A woman is red-green color-blind. What can we conclude, if anything, about her father?

He is red-green color-blind.

-A normal male cannot father a red-green color-blind daughter.


A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind?



Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele.

-Moreover, males carrying the allele have less of an opportunity to have offspring.


Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia.


-The mother is XHXh, and the father is XhY. The daughter must receive Xh from the father and has a 50% chance of receiving Xh from the mother.


Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.


In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome?

Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.


A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by _____.

X chromosome inactivation


With a microscope, you examine some somatic cells from a woman and notice that each nucleus has two Barr bodies. What can you infer about the sex chromosomes in this individual?

She is XXX.


X-linked genes differ from Y-linked genes in which of the following ways?

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.


Which of the following best describes the function of the XIST gene in X chromosome inactivation?

The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.


If two genes are linked, _____.

they are on the same chromosome


In a particular species of mammal, black hair (B) is dominant to green hair (b), and red eyes (R) are dominant to white eyes (r). When a BbRr individual is mated with a bbrr individual, offspring are produced in a ratio of 5 black hair and red eyes:5 green hair and white eyes:1 black hair and white eyes:1 green hair and red eyes. Which of these explanations accounts for this ratio?

The genes for hair color and eye color are linked.


A gray-bodied, vestigial-winged fly is crossed with a black-bodied, normal-winged fly. The F1 progeny is testcrossed. Among the resulting offspring, _____ is a parental type, and _____ is a recombinant type.

black-bodied, normal-winged ... black-bodied, vestigial-winged


You perform a testcross using F1 dihybrid flies. If, in the resulting offspring, the percentages of parental and recombinant offspring are about the same, this would indicate that the two genes are _____.


-Two genes on different chromosomes assort independently.


The recombination frequency between two gene loci is _____.

greater as the distance between the two loci increases


Four genes (A, B, C, and D) are on the same chromosome. The recombination frequencies are as follows: A-B: 19%; B-C: 14%; A-C: 5%; B-D: 2%; A-D: 21%; C-D: 16%. Based on this information, which sequence of genes is correct?


-C must lie between A and B (5 +14 = 19). Similarly, D must be beyond B to be 21 units from A and 2 units from B.


In question 18, the observed distribution of offspring was as follows: black-red 1,070; black-white 177; green-red 180; green-white 1,072. Based on these data, what is the recombination frequency?

approximately 14%

-Recombination frequency = (number of recombinants)/(total offspring) × 100.


A linkage map _____.

orders genes on a chromosome based on recombination frequencies


Because the frequency of crossing over is not uniform along the length of a chromosome, _____.

map units do not necessarily correlate to physical distances along the chromosome


Which of the following would result in genetic variation by way of new combinations of alleles?

-independent alignment of homologous chromosomes during meiosis I
-the exchange of alleles between homologous chromosomes during meiosis I
-random fertilization increasing the number of possible allele combinations in an individual


need to add the concepts after 15.3.

this only has concepts 15.1,15.2, and 15.3


What can we observe in order to visualize Mendel's Law of Segregation?

homologous chromosomes separating during meiosis I

-Homologous chromosomes each carry an allele for every gene. Those alleles may be the same or different, but they are segregated during meiosis I and distributed to each gamete.


What name is given to the most common phenotype in a natural population?

wild type

-The most common phenotype is the wild type.


A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?

None of the females will have white eyes.

-All of the females will have red eyes because they will inherit the dominant red-eye allele from their male parent.


In humans, what determines the sex of offspring and why?

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome.

-In humans, the male produces both X- and Y-bearing sperm, whereas females only produce X-bearing eggs.


Which of the following is true of an X-linked gene, but not of a Y-linked gene?

The gene is present in both males and females.

-All cells have at least one functional X chromosome.


In general, the frequency with which crossing over occurs between two linked genes depends on what?

how far apart they are on the chromosome

-The farther apart two genes are, the greater the probability that a crossover will occur between them, and therefore the greater the recombination frequency.


Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?


-An aneuploid individual has either too many or too few chromosomes, usually as a result of nondisjunction.


What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?

an inversion


What phenomenon occurs when a particular allele will either be expressed or silenced, depending on whether it is inherited from a male or a female?

genomic imprinting

-The sex of the parent transmitting a given chromosome can affect the chromosome's expression in the offspring.


How are human mitochondria inherited?

from the mother only

-An individual's mitochondria are all derived from those found in the ovum.


Hemophilia is caused by a sex-linked recessive gene. I am sure that i do not have hemophilia. What genotype must i be?

X^H Y^0

-Since hemophilia is sex-linked, I must have only one copy of the gene, on my X chromosome. And since I don’t have the recessive disorder, I must have the dominant form of the gene.


Consider the hypothetical sex-linked recessive baldness gene. If a bald woman has a child with a normal male, what are the odds that their son will be bald?


-If a woman is bald, she must have two copies of the recessive gene, so she must pass one on to her children. Since her son would get his Y chromosome from his father and his X chromosome from his mother, he would inherit her baldness gene. That means that all of her sons will be bald.


What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

-Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.


When can nondisjunction occur?

-In mitosis, when sister chromatids fail to separate
-In meiosis, when sister chromatids fail to separate
-In meiosis, when homologous chromosomes fail to separate

--Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.


Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome

-Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.


What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell

-A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.


Of the following chromosomal abnormalities, which type is most likely to be viable in humans?


-Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.


If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

-When this error occurs in meiosis II, only half of the gametes are affected.


If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

-When this type of error occurs, half of the gametes receive one too many chromosomes, and the other half receive one too few. When all of the gametes are affected, the error probably occurred in meiosis I.


Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete?


-Meiosis cuts the number of chromosomal sets in half.


Humans are diploid and have 46 chromosomes. How many chromosomes are found in each human gamete?


-23 is one-half of 46


_____ is the process by which haploid gametes form a diploid zygote.


-The joining of haploid gametes produces a diploid zygote.


A particular diploid plant species has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have _____ set(s) of chromosomes.


-If self-fertilization occurs, and two gametes (each having 48 chromosomes) unite, the zygote will have 96 chromosomes (or 4 sets).


Which of these terms applies to an organism with extra sets of chromosomes?


-Polyploid individuals have more than two complete sets of chromosomes.


Mutant tetraploid plants _____.

are unable to interbreed with a diploid plant

-This is why polyploidy is a mechanisms of plant speciation.


Most polyploid plants arise as a result of _____.


- Most polyploid plants are the result of the hybridization of two different parental species.


Cystic fibrosis is an inherited disorder that affects which of the following?



How long can sperm be cryogenically stored and still be viable?

for more than 20 years


As an expecting mother of 42 years of age, you are saddened to learn that the results of a prenatal test came back positive for trisomy 21. Although you are distraught by your circumstances, you are somewhat relieved to find out that the Prenatally and Postnatally Diagnosed Conditions Awareness Act was enacted to _____.

require medical practitioners to provide up-to-date, evidence-based information to parents about any prenatal or postnatal diagnosis for a trisomy condition, and connect the parents with appropriate support services


Individuals with an extra X chromosome _____.

may have subnormal intelligence or be at risk for learning disabilities


During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.



In Klinefelter syndrome, individuals are phenotypically male, but they have reduced sperm production and may have some breast development in adolescence. The cells of Klinefelter individuals have two X chromosomes and one Y (they are XXY instead of XY). This occurs because of what meiotic error?



Cells that have a number of chromosomes different from the normal number for their species are known as _____.



_____ is usually less severe than _____, and _____ species have been observed in plants, fish, amphibians, and even mammals.

Polyploidy ... aneuploidy ... polyploid


Gene A is normally found on chromosome number 15 in humans. If amniocentesis reveals fetal cells containing gene A on chromosome 17, but not on 15, the best explanation would be that _____.

translocation occurred

-Fragments produced by chromosomal breakage may join nonhomologous chromosomes, a rearrangement known as a translocation.


The chromosomal abnormality in which a fragment of a chromosome breaks off and then reattaches to the original chromosome in the same place but in the reverse direction is called _____.



Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?

Extra copies of the other chromosomes are probably fatal to the developing embryo.


When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of _____ and results from _____.

aneuploidy ... nondisjunction of chromosome 21 during meiosis I


A person with two X chromosomes and one Y chromosome would appear to be _____.


-The presence of the Y chromosome determines maleness in humans. A male with an extra X chromosome has Klinefelter syndrome.


Which of the following is the only known viable human monosomy?



Which type of chromosomal alteration is responsible for the cri du chat syndrome?



What appears to be the mechanism for genomic imprinting?

-DNA methylation that silences particular genes
-DNA methylation that activates particular genes

--DNA methylation appears to be the major mechanism involved in genomic imprinting, but in come cases it silences a gene and in others it activates a gene.


Genomic imprinting in mammals appears to affect primarily genes involved in _____.

embryonic development

- Igf2 is an example of a growth factor required for normal prenatal development. Experiments have also shown that organisms with improperly imprinted genes often die before birth.


Both chloroplasts and mitochondria _____.

carry extranuclear genes


It is proposed that a certain disorder affecting the inner ear is caused by mitochondrial DNA. Which of the following observations would be the most decisive evidence against this idea?

Fathers with the disorder pass it on to all their children, but mothers with the disorder do not pass it along.

-Maternal inheritance is the rule for mitochondrial genes in mammals, because the mitochondria in the zygote all come from the cytoplasm of the egg.


A person's remains are found, and officials are trying to identify them. A couple believes that the remains belong to their missing daughter. Because the remains have decayed considerably, mitochondrial DNA is being used to determine the person's identity. In order to determine if the remains belong to someone in this couple's family, whose mitochondrial DNA should be used for comparison?

one of the couple's other children

-Although the husband would have inherited his mitochondrial DNA from his mother, he would not have passed it on to his children.


A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all four will be born with hemophilia?



Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.

Recessive; if the disorder were dominant, it would affect at least one parent of a child born with the disorder. The disorder's inheritance is sex-linked because it is seen only in boys. For a girl to have the disorder, she would have to inherit recessive alleles from both parents. This would be very rare, since males with the recessive allele on their X chromosome die in their early teens.


A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild-type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size?



What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?

The disorder would always be inherited from the mother.