Third Test

The blending hypothesis, but not the _______________, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity.

particulate hypothesis

If a plant variety is true-breeding for a dominant trait, the ___________

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

A=big apples; R=red apples; a=small apples; r=yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and hal produce big yellow apples. What are the genotypes of the parents?

AArr and aaRr

Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will be ______


The F1 generation differed from the F2 in Medel's experiments in that ________

all of the F1 showed the dominant phenotype, but only three-fourths of the F2 did

Physically, what are different alleles?

Different alleles are different DNA sequences found at the same locus on homologous chromosomes

In a certain plant, the alleles, A, B and C are completely dominant to the alleles a, b and c. A plant with the genotype AABbcc will have the same phenotype as a plant with the genotype ____________


Pea plants are tall if they have the genotype TT or Tt, and they are short if they have the genotype tt. A tall plant is mated with a short plant. What would the outcome be that would indicate that the tall parents plant was heterozygous?

The ratio of tall offspring to short offspring is 1:1

What is indicated when a single character testcross yields offspring that all have the dominant phenotype?

The parent with the dominant phenotype was homozygous

If an organism that is homozygous dominant is crossed with a heterozygote for that trait, the offspring will be ________

all of the dominant phenotype

In Mendel's monohybrid cross of purple-flowered and white-flowered peas, all members of the F1 generation had the ______ phenotype because their genotype was _ at the flower-color locus.

purple flowered, heterozygous

If the two traits that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located near each otheron the same chromosome, then the F2 generation ______________

would have deviated from 9:3:3:1 phenotype ratio that is predicted by the law of independant assortment.

The law of indepentant assortment _

the first, second and third answers are correct

Homologous paris of chromosomes often

contain different alleles

If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?


Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What portion of the offspring from the cross PpRr xPpRr will have white flowers and wrinkled seeds?


An AABbccDdEeFF individual is crossed with an individual with the genotype AaBBCCDdEeff. What is the probability that their offspring will have the genotype AaBBCcddEEFf?


If a heterozygous plant is aallowed to self-pollinate, what proportion of the offspring will also be heterozygous?


An individual with the genotype AABbCcDD can make how many different kinds of gametes?


A red bull is crossed with a white cow and all of the offspring are roan, an intermediate color that is caused by the presence of both red and white hairs. This is an example of genes that are _________


Flower color in snapdragons is an example of incomplete dominance. When a red-flowered plant is crossed with a white-flowered, the F1 generation has pink flowers. If a pink flowered plant is crossed with another pink-flowered plant, the progeny plants will be _____

25% red, 50% pink and 25 % white

What best describes the expression of Tay-Sachs disorder in humans at the biochemical level?

incompletely dominant

Human blood groups are governed by three alleles, A, B and O. A and B are codominant while O is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

A, B, AB or O

What mating cannot produce a child with a blood type O? The letters refer to blood types (phenotypes)

O x AB

A woman with type O os expecting a child. Her husband is type A. Both the woman's father and her husband's father had type B blood. What is the probability that the child will have type O blood?


A single genetic locu that controls more than one trait is said to be


Color in squash is controlled by epistastic interactions in which color is recessive to no color. At the first locus white squash (W) is dominant to colored squash (w). At the second locus (Y) is dominant to green (y). What is the phenotype of a squash with the genotype wwYy?


Tail length in a certain species of armadillo falls along a continuum, following a normal distribution. Assuming that environmental do not play an important roll in determining tail length, this type of variation probably reflects ______________

polygenic inheritence

Mendel's theory of particulate inheritance can explain ___________

inheritance patterns for virtually every sexually-reproducing organism but does not explain multifactorial characters

Tay-Sachs disease runs in Rebecca's family. On a family pedigree, she saw a shaded circle. This represented __

female with Tay-Sachs

A man who can roll his tongue and a woman who can roll her tongue have a sonb who can roll his tongue (R=can roll tongue;r= can't roll tongue). The son is curious aout whether is father is homozygous or heterozygous for the tongue-rolling trait. What would allow him to know?

His father's mother cannot roll her tongue.

Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder. If alkaptonuria is like most other human hereditary disorders, the probability of their next child beign born with the disease is ________--


Tom's brother suffers from phenylketonuria (PKU), a recessive disorder. The brothers' parents do not have PKU. What are the chances that Tom, who is normal for this trait is a carrier for PKU?


A couple, both descended from eastern European Jews, visit a genetic councelor before trying to have children. in view of their ethnic background, the councelor recomends that they be tested to see if they are carriers for _______________


Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Why do cases continue to arise, even though people with the disease rarely live to reproduce?

Because the harmful allele "hides" within heterozygous individuals, one fourth of the offspring of two heterozygotes would be afflicted

The genetic disease cystic fibrosis is caused by a defective allele that

encodes a defective chloride-channel membrane transport protein

In people with sickle cell disease, red blood cells break down, clump and clog the blood vessels. The blood vessels and tghe broken cells accumulate in the spleen. Among other things this leads to physical weakness, heart failure, joint pain, and brain damage. Such a suite of symptoms can be explained by ___________

the pleiotropic effects of the sickle cell allele

When two average height parents give birth to a child exhibiting achondroplasia, it is most likely due to a new mutaiotn. This is because _

achondroplasia is caused by an allele that is always expressed, therefore the parents must not have the allele

It is more common to find human genetic disease caused by ________ alleles than nby ____________ alleles because _______

recessive; dominant; hamrful recessive alleles can survive in the heterozygote without any selection pressure against them.

Huntington's disease is an example of a genetic disorder caused by ________

a lethal dominant allele that afflicts an individual later in life

Heart disease, diabetes, cancer, alcoholism and many mental illnesses can best be described as _______________

multifactoral disorders with a possible polygenic componant

Fetal cells may be removed laong with fluid from the womb by a process known as _________________


What genetic testing procedure would a physician remove a small tissue sample from a membrane of fetal genetic origin?

chorionic villus sampling

The chromosome theory of inheritance states that _________

The first, second and third answers are correct

Why did Morgan choose Drosphilia for his genetics experiments?

both b and d (A single mating can produce many offspring/Drosphilia 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

What result of Thomas Hunt Morgan's experiments with white eyes 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

In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (SEx determination is 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?


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

He is red-green color blind

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

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


Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which one 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.

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

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 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 explainations 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 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 _________


The recombination frequency between two gene loci is _________

greater as the distance between the two loci increases

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

During meiosis, homologous chromosomes sometimes :stick together" and do not seperate 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 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 occured

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; nondisjuntion of chromosome 21 during meiosis I

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


What 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?

both a and c

Genomic imprinting in mammals appears to affect primarily genes involved in ___________

embryonic development

Both chloroplasts and mitochondria ____________

carry extranuclear genes

Viruses can vary with respect to all of the following characteristics except ___________

the presence or absence of metabolic machinery

A microbiologist analyzes chemicals obstained from an enveloped RNA virus that infects monkeys. He finds that the viral envelope contains a protein characteristic of monkey cells. What is the most likely explanation?

The viral envelope forms as the virus leaves the host cell

Which, if any, may be a componant if a virus?

all of the above

Viruses that infect bacteria are called __________


HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _________

the virus binds to specific receptors that are only present on certain immune cells

Cancer cells often have protein receptor molecules on their surfaces that differ from those on normal body cells. Given this fact, how might viruses be used to treat cancer?

viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells

Why are phages useful in treating bacterial infections in humans?

The first three answers are correct

Which of the following can a virus do without a host cell?

none of the above

When a virus infects an E. coli, what part of the virus enters the bacterial cytoplasm?

only the nucleic acid

The phage reproductive cycle that kills the bacterial host cell is a _______ cycle, and a phage that always reproduces this way is a __________

lytic; virulent

In the lytic cycle of phages __________

the cell typically dies, releasing many copies of the virus

Restriction enzymes help defend bacteria against viral infections by ___________

cutting viral DNA once it has entered the cell

A phage that inserts itself into the host DNA is called __________


A prophage is a __________

viral genome that has been incorporated into a bacterial cell's chromosome

In the lysogenic cycle of phages _________

all of the above

Why can flare-ups of the herpes virus recur throughout a person's life?

Herpes can leave its DNA behind as minichromosomes in nerve cell nuclei. Stree can trigger another round of virus production, producing characteristic blisters and sores.

How do retroviruses, such as HIV differ from other viruses?

They contain the enzyme reverse transcriptase

Reverse transcription, carried out by retroviruses, is the process by which ___________

RNA information is copied into DNA

What statement is a correct comparison of a "regular" RNA virus and a RNA retrovirus?

Both produce protein coats via translation of mRNA

When comparing DNA and RNA viruses, which mutate more quickly, and why?

RNA viruses because no proofreading is done on RNA molecules

The symptoms of a viral infection in a person can by caused by _________

all of the above

Vaccines for viral diseases are _____ and help prevent infection by _______

harmless derivatives of pathogenic viruses; stimulating the immune system to mount a defense against the actual pathogen

What is an example of vertical transmission of a virus in plants?

an infected plant produces seeds that contain the virus, giving rise to infected progeny

Prions are __ that are thought to cause disease by _________

abnormally shaped proteins; inducing similar but normally shaped proteins in the brain to adopt the abnormal form

A heritable feature that varies among individuals is called ______________

a character

Each variant for a characteristic is called a ______________


The mating or crossing of two true-breeding varieties is called


True-breeding parents are referred to as the

P generation

Hybrid offspring from two true-breeding parents are called ______. The self-pollinated offspring of these are called _____________

F1; F2

Mendel's first law, stating that the two alleles in a pair segregate into different gametes during gamete formation

The Law of Segregation

Mendel's second law states that each pair of alleles segregates independently of each other pair during gamete formation.

Law of Independent Assortment

Alleles are _____________

alternative versions of a gene

An organism that has a pair of identical alleles for a character is said to be _______________- for the gene controlling that character


An organism that has two different alleles for a gene is said to be ________________ for that gene


Observable traits are called an organism's


An organism's genetic makeup is called its


The genotypic ratio is


The phenotypic ratio is


breeding an organism of unknown genotype with a recessive homozygote is called a _______________