Biology

Chromosome number is reduced during meiosis because the process includes

a cell division in which homologous chromosomes are separated from each other.

In sexually reproducing organisms, the diploid phase of the life cycle begins at

fertilization

In a diploid organism, zygotes are

diploid

Suppose members of a true-breeding strain of salamanders with yellow stripes are crossed with a true-breeding strain with red stripes. Red and yellow are two alleles of the same gene. The resulting offspring all have yellow stripes and red stripes. Which dominance pattern is most consistent with the observations?

Red and yellow stripes exhibit codominance.

In a population of hamsters, some individuals have the nucleotide G at one place in a gene and some have the nucleotide A in the same place. Stating that an individual has copies of both G and A characterizes that individual’s _______, and that individual is a _______.

genotype; heterozygote

If Mendel had performed experiments on cattle rather than on peas, the patterns of inheritance would not have been easily detectable, because cattle

have small numbers of offspring.

The concept of _______ describes the dual contribution of genetic and environmental factors to the phenotypic variation exhibited by many traits that are affected by multiple genes.

phenotypic plasticity

Very few chromosome abnormalities (extra or not enough chromosomes) are observed in the human population because

they are usually lethal and often cause spontaneous abortion of the embryo.

An individual with three copies of one chromosome has 27 chromosomes. What is the haploid chromosome number?

13

The haploid chromosome number of a human cell is 23. How many chromosomes will a trisomic individual have?

47

The copying of a DNA sequence to make an RNA sequence is called

transcription

The short “starter” strand used in DNA replication is called the _______. In most organisms, it is made of _______.

primer; RNA

The enzyme DNA ligase is required continuously during DNA replication because

fragments of the lagging strand must be joined together

Which statement about the semiconservative replication of DNA is true?

Each of the original strands acts as a template for a new strand.

The poly(A) tail added to a primary transcript

increases mRNA stability.

What is the sequence of the complementary strand of RNA made from the template DNA sequence 5′-CAGCGGTTCGCTGAAGTC-3′?

3′-GUCGCCAAGCGACUUCAG-5′

During transcription, what molecule unwinds the DNA?

RNA polymerase

The _______ facilitate the transport of processed mRNAs out of the nucleus.

poly(A) tails

Which statement about RNA is false?

Ribosomal RNA functions in translation.

The anticodon 3′'-AUC-5′ would pair with the codon

5′-UAG-3′.

Which statement about the genetic code is true?

The genetic code evolved in the common ancestor of all known life.

A stretch of 150 nucleotides in an exon of a gene would code for _______ codons and _______ amino acids.

50; 50

Suppose that a certain enzyme is not synthesized in bacteria whenever the solution in which the cells are growing contains substance Y. When substance Y is not present, the enzyme is produced. This phenomenon would most likely be an example of _______ gene regulation.

negative

A difference between promoters and operators is that

RNA polymerase binds within the promoter, while a repressor binds the operator.

Suppose that a certain enzyme is not synthesized in bacteria whenever the solution in which the cells are growing lacks substance X. When substance X is present, the bacteria produce the enzyme. This phenomenon would most likely be an example of _______ gene regulation.

positive

A triploid plant has

one extra set of chromosomes.

A silent mutation

would not affect the primary structure of a protein.

A point mutation causes a change in the amino acid sequence in the encoded protein. This is an example of a _______ mutation.

missense

Which of the following does not regulate gene expression after transcription?

Transcription factor binding

In the liver cells of a mouse, an enzyme contains exons 1, 3, and 5. In the mouse’s cardiac tissue, this same enzyme contains exons 1, 2, 4, and 5. These differences result in different catalytic functions of the enzyme. This is an example of

alternative splicing.

In eukaryotic cells, an enhancer

bound by transcription factors will result in increased transcription rates.

Evolution is the change in the genetic makeup of

populations of organisms over time.

The biological species concept emphasizes whether populations

can have gene flow between them.

Which is a key point in Darwin’s explanation of evolution?

Any trait that confers an increase in the probability of survival and reproduction will increase in frequency in the population.

Which definition describes a vestigial structure?

Structures that were once useful and functional but are no longer.

Which is a prezygotic isolating mechanism?

Incompatibility between gametes

Suppose individual robins with longer beaks have somewhat more offspring than those with shorter beaks, and that this has led to increases in beak length in the robin population over time. We can say that beak size is associated with the _______ of the robin, and that there is _______ selection operating on beak size.

fitness; directional

A lineage of fossil mammals shows unusual stability over time for size. Modeling and statistical analysis rule out genetic drift as an explanation for the pattern. What is the most likely cause for this pattern?

Stabilizing selection

What is genetic drift?

The random change in allele frequencies from generation to generation.

How can scientists conclusively measure when evolution has occurred?

By calculating allele or genotypic frequencies of different generations and noting any change.

Present day pythons have structures that are known as pelvic spurs. These are very small bones that resemble a pelvis and femur. They are not connected to the vertebrae of the snake, but rather lie within muscle tissue. They may protrude from the body like a claw covered with hard tissue. The spurs can be used by male pythons for clasping during mating. Based on this information, which could be a hypothesis regarding the purpose of the pelvic spur?

The pelvic spurs have developed over time as courtship and mating rituals among pythons has changed.

Which sequence gives the correct ordering of levels from smallest to largest?

Organism, population, community, ecosystem

Of these trophic levels, which one obtains all its nutrients from inorganic sources?

Primary producers

Grain is eaten by cows, and cows are eaten by humans. If the ecological transfer efficiency between each trophic level is 10 percent, how much grain is required to produce 70 kg of human biomass?

7,000 kg

In this food web, grizzly bears, coyotes, and ravens are all competing for which resource?

Berries

Breeding salmon use a combination of magnetic field detection and sense of smell to swim from the ocean to their upstream birthplace. After an accidental discharge of chemicals into a stream, researchers noted that the salmon stopped returning to this stream. Can you explain what likely occurred?

The chemical contaminants interfered with the navigation cues used by the salmon.

Lions often hunt together in packs. Which of the following observations would suggest that this behavior is an evolutionary adaptation?

Lions that hunt in packs can kill a greater mass of prey per capita than lions that hunt in isolation.

Which behavior is an example of operant conditioning?

Training a mouse to push a lever by rewarding it with food when the lever is pressed

Endotherms can live in a wider range of environments. With reference to this fact, which trade-offs do endotherms exhibit relative to ectotherms?

Endotherms must consume more food resources than ectotherms.

What type of organisms would be two trophic levels removed from autotrophs?

Secondary consumer

In an organism with a diploid number of 8, a gamete has _______ chromosomes and a liver cell has _______ chromosomes.

4; 8

Diploid cells of the fruit fly Drosophila have eight chromosomes. How many chromosomes does a Drosophila gamete have?

4

In a simple Mendelian monohybrid cross, true-breeding tall plants are crossed with short plants, and the F₁ plants, which are all tall, are allowed to self-pollinate. What fraction of the F₂ generation will be both tall and heterozygous?

1/2

Which statement about an individual that is homozygous for an allele is false?

Its parents were necessarily homozygous for that allele.

The fact that most monosomies (the inheritance of only one chromosome of a homologous pair) and trisomies (the inheritance of one extra chromosome) are lethal to human embryos illustrates the

importance of the orderly distribution of genetic material during meiosis.

Down syndrome (also known as trisomy 21) can be diagnosed by means of an examination of the individual’s

karyotype.

The haploid number in Drosophila melanogaster is 4. How many chromosomes would an individual with a trisomy have?

9

DNA carries genetic information in its

sequence of bases.

The short “starter” strand used in DNA replication is called the _______. In most organisms, it is made of _______.

primer; RNA

Although DNA is made up of only four different bases, it can encode the information necessary to specify the workings of an entire organism. It can do this because DNA

molecules are extremely long.

Which letter represents the leading strand?

a

If a template DNA strand has the base sequence 3′-GTC…CCA-5′, what would be the sequence of the corresponding mRNA? (Note: “…” represents an intervening sequence.)

5′-CAG…GGU-3′

Transcription is the process by which

an RNA molecule is synthesized from a DNA template.

During which stage would you expect promoters to play a role?

Initiation of transcription

All cells in a multicellular organism

contain the same genome.

If a codon is 5′-AAG-3′, the anticodon is

3′-UUC-5′.

An mRNA molecule has a coding region with 540 codons. This coding region has _______ nucleotides.

1620

In a bacterial operon, the binding of the inducer to the repressor causes the repressor to

stop binding to the operator.

In _______ regulation, a repressor binds a specific site in or near the promoter to _______ transcription.

negative; decrease

Suppose that a certain enzyme is not synthesized in bacteria whenever the solution in which the cells are growing lacks substance X. When substance X is present, the bacteria produce the enzyme. This phenomenon would most likely be an example of _______ gene regulation.

positive

In sickle-cell disease, a change in one base pair results in one amino acid being substituted for another in the β-globin protein. This type of mutation is referred to as a _______ mutation.

point

Which statement about mutations is correct?

Mutations can be induced by outside environmental factors.

Mutations

are alterations in an organism’s DNA.

A mutation in an enhancer for a specific gene reduces the enhancer’s ability to be bound by proteins. Which consequence is most likely?

The rate of transcription of this particular gene will be reduced, even when it is needed.

Which of the following does not regulate gene expression after transcription?

Transcription factor binding

Transcription factors

regulate how much RNA will be produced from DNA.

Suppose two species of morning glory flowers are reproductively isolated because one species blooms in early April and in the other species blooms in mid-May. This would be an example of _______ isolation, which is a form of _______ isolation.

temporal; prezygotic

Which of the following is required for natural selection to occur?

A trait must be heritable so that it is capable of being passed on to future generations.

If this population were subject to stabilizing selection for several generations, which, if any, of the distributions shown would be most likely to result?

a

A wildfire in Australia left only 10% of a population of koala bears. This event likely led to a shift in the allele frequencies of the population. This situation is known as

a bottleneck.

Suppose a hard frost in southern Florida kills nearly all of a population of plants. Even though the plant population recovers in numbers after a couple of decades, the genetic variation within that population remains much reduced. What is the most likely cause of the diminished genetic variation?

Population bottleneck

The RNA world hypothesis states that RNA was the original information-storage molecule in the earliest forms of life on Earth. What properties of RNA lead scientists to believe this hypothesis?

RNA can store and transmit information and facilitate chemical reactions.

Which is a prezygotic isolating mechanism?

Incompatibility between gametes

Mutations are a significant source of genetic variation that contribute to evolutionary change. How do mutations arise?

From random errors in the DNA replication process

Which statement about sexual selection is true?

Traits favored by sexual selection are often costly to males.

What is the main difference between innate and learned behavior?

Innate behaviors are instinctive; learned behaviors are acquired through experience.

Which is an example of an ecosystem with high resilience?

A temperate forest that quickly regrows following a severe wildfire

Which is a similarity between cellular respiration and carbon combustion?

Both processes break down large carbon molecules into CO₂.

The term population density is defined as the

number of individuals in an area divided by the size of the area.

Which example is a mutualistic interaction?

A bacterial species lives inside a plant’s roots and provides usable nitrogen to the plant, which in turn provides sugar nutrients to the bacteria.

Density dependent factors are commonly associated with

carrying capacities.

Each diploid cell of a human female contains how many of each type of chromosome?

46

As a result of fertilization, the number of chromosomes in the zygote _______ in comparison to that in each of the gametes.

stays the same in plants and animals

If a trait that is not expressed in the F₁ generation reappears in the F₂ generation, the inheritance of the trait in question is an example of

a recessive trait.

Which statement best expresses the concept of phenotypic plasticity?

A mutation affecting coat color exhibits recessive inheritance.
e. Light levels affect the rate of photosynthesis of genetically identical seedlings

DNA with a higher G and C content is more stable at high temperatures than DNA with a high A and T content. Why?

Each G-C pair forms three hydrogen bonds between antiparallel strands, whereas each A-T pair forms just two.

Although DNA is made up of only four different bases, it can encode the information necessary to specify the workings of an entire organism. It can do this because DNA

is eventually translated into proteins, which are made up of 20 different amino acids.

Purines include

adenine and guanine.

If pyrimidines could bind to other pyrimidines, and purines could bind to other purines, what would be the impact on the DNA double helix?

The width of the double helix would vary rather than having a fixed width.

You are least likely to see introns in a(n)

bacterial genome.