Ch. 9-12
What is the most common autosomal trisomy at birth?
Down syndrome, affecting chromosome 21 An extra copy of chromosome 21, a condition called trisomy 21, or Down syndrome, occurs in about 1:700 births. This rate varies tremendously with the age of the parents.
Metaphase
The mitotic spindle is fully formed and chromosomes are lined up in the center of the cell
Which of the following events occurs during prophase?
The spindle microtubules form. The spindle microtubules must form before DNA can be sorted and divided.
What do the three major checkpoints for cell division have in common?
They all focus on DNA and chromosomes. All three checkpoints focus on the readiness of the cell based on DNA replication and sorting of the chromosomes.
Homologous chromosomes migrate to opposite poles during _____.
anaphase I During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.
During which phase of the cell cycle do the alleles separate independently of one another (which is what Mendel called the law of independent assortment during meiosis)?
anaphase I Homologous chromosomes separate during anaphase I. During anaphase II, the sister chromatids (often identical to one another) become unlinked and separate from each other.
During which phase of meiosis does the law of segregation of alleles occur?
anaphase I Homologues separate during anaphase I. Sister chromatids separate during anaphase II.
The result of the following cross indicates that genotypically the offspring
are all Bb This cross indicates that the flat headtop allele is dominant to the wild-type headtop allele, so all offspring are indeed Bb.
_________________ reproduction occurs without the union of two reproductive cells.
asexual
A(n) ____________ is any chromosome other than a sex chromosome.
autosome
Scientists can perform a process called polymerase chain reaction in the lab to copy DNA inside a test tube. This method is part of creating a DNA fingerprint of a suspected criminal. Cells from the suspect's cheek are placed into a tube. They are popped open, and all the proteins and lipids are removed from the solution. The strands of DNA are separated by heating, and polymerase is added to copy the DNA. What necessary component of DNA replication has been left out of this description?
free nucleotides New DNA cannot be synthesized without the monomers from which it is built.
Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.
genetic drift Modern travel and migration decreases the chances of there being a small, isolated population.
The complete sequence of DNA in a given organism is called the __________.
genome The genome consists of all the nucleotides in the DNA. A genome may contain millions or billions of nucleotides.
An organism's genetic makeup--its actual combination of alleles--is known as its ______________.
genotype
An individual heterozygous for eye color, skin color, and number of eyes mates with an individual who is homozygous recessive for all three characters; what would be the expected phenotypic ratio of their offspring? [Hint: B = black eyes, b = orangeeyes; G = green skin, g = white skin; C = two eyes, c = one eye]
1 black eyes, green skin, two eyes : 1 black eyes, green skin, one eye : 1 black eyes, white skin, two eyes : 1 black eyes, white skin, one eye : 1 orange eyes, green skin, two eyes : 1 orange eyes, green skin, one eye : 1 orange eyes, white skin, two `eyes : 1 orange eyes, white skin, one eye This is a tough problem; you had to expand your Punnett square to accommodate another character. However, 1:1:1:1:1:1:1:1 ratio is the expected outcome of a BbGgCc x ooggcc cross.
The prokaryotic cell cycle has 5 distinct stages:
1.The single prokaryotic chromosome is usually attached to the plasma membrane of the cell 2.Chromosome replicates, producing two identical copies, that attach to plasma membrane at nearby, but separate, sites 3.As the cell increases in size, new plasma membrane is added, pushing chromosomes apart 4.The plasma membrane grows inward between the two chromosome copies 5.The parent cell divides into two daughter cells, with each one genetically identical to the parent cell and containing a single, circular chromosome
At the time of fertilization in humans, two gametes, each containing a unique combination of alleles, fuse to form a diploid offspring. If you ignore crossing over, a single person can produce gametes with roughly how many different chromosome combinations?
8 Million In humans, a single person can produce gametes with any of 8 million chromosome combinations.
Mendel performed crosses that involved two different genes, each with two different alleles. If he allowed a plant to self-fertilize that was heterozygote for these two traits, such as SsYy, what ratio of the plants did he find expressed the dominant trait for both genes in the resulting phenotype?
9 of 16 Mendel found that the ratio of a hybrid cross involving two traits follows the law of independent assortment. This will result in a phenotypic ratio of 9:3:3:1, where 9 out of 16 represents the ratio of the expression of the dominant trait for each of the two genes.
The prokaryotic cell cycle has five distinct stages. What would be the correct order of these five stages (from beginning to end) using the five statements below? A: As the cell increases in size, new plasma membrane is added, pushing chromosomes apart. B: The parent cell divides into two daughter cells, with each one genetically identical to the parent cell and containing a single, circular chromosome. C: The single prokaryotic chromosome is usually attached to the plasma membrane of the cell. D: The chromosome replicates, producing two identical copies that attach to plasma membrane at nearby, but separate, sites. E: The plasma membrane grows inward between the two chromosome copies.
C, D, A, E, B This would be the correct sequence of events for the prokaryotic cell cycle. Refer to Figure 9-4b in the textbook for more information.
The radioactive isotope 32P labels the T2 phage's _____.
DNA The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.
The copying of a DNA strand is said to be semiconservative. Why is this word used rather than calling it simply duplicated?
Each half of the original DNA strand is kept and used as the template or model strand for the polymerase enzyme to match the base pairs to complement the original side. This results in two new and identical copies of DNA replicated from half the strand of the original DNA molecule.
How are homologous chromosomes defined?
Homologous chromosomes contain the same genes but may contain different alleles. Homologous chromosomes have identical genes but may have different varieties of that gene called alleles (brown hair versus black hair).
Which of the following statements is false regarding homologous chromosomes?
Homologous chromosomes separate during anaphase II in meiosis II.
Which of the following is not true of human chromosomes?
Human gametes end up with two of each type of 23 chromosomes. This statement is incorrect because the process of meiosis produces haploid cells, which have one of each chromosome type (they are not in pairs) and in humans that number would be N = 23.
Cell Cycle (Two Main Phases and Key Stages)
Interphase (large blue area), Mitotic Phase (small orange part), Mitosis and Cytokinesis are apart of the Mitotic Phase, G1, S, and G2 Phase are apart of Interphase
Victoria Queen of England had several children, including those shown on the pedigree. Which of Victoria's children inherited the hemophilia allele from her?
Leopold Duke of Albany, Alice Princess of Hesse, and Beatrice Princess of Battenberg Sex chromosomes are XX in females and XY in males. Victoria Queen of England, the first carrier female on the pedigree, carried the hemophilia allele on one of her X chromosomes. She passed her affected X chromosome to several of her children, including Leopold Duke of Albany, Alice Princess of Hesse, and Beatrice Princess of Battenberg.Because Leopold only had one X chromosome, and it was affected, he exhibited the disease. But, because the disease is recessive (meaning that one normal allele will prevent the expression of the disease), and Alice and Beatrice both had one affected X chromosome and one normal X chromosome, they did not exhibit the disease.
Why do males suffer from sex-linked disorders more often than females?
Males can express single recessive alleles from their single X chromosome. A female would require two recessive alleles (one on each of her two X sex chromosomes for the 23rd pair) for any gene to express the recessive allele.
A BbGg x bbgg cross yields a phenotypic ratio of approximately 5 black eyes, green skin : 5 orange eyes, white skin : 1 black eyes, white skin : 1 orange eyes, green skin. Which of the following best explains these results?
Mendel's law of independent assortment is being violated. If the genes for eye color and skin color assorted independently, then the outcome of this cross would have been a 1:1:1:1 ratio.`
That each gamete contains a single allele of the eye color gene is an illustration of _________.
Mendel's law of segregation only Mendel's law of segregation is based on gametes getting only one copy of each allele of each gene.
The observed distribution of alleles into gametes is an illustration of _____.
Mendel's laws of segregation and independent assortment The events seen here illustrate both the law of segregation and the law of independent assortment.
What must happen before a cell can begin mitosis?
The chromosomes must be duplicated. Before mitosis can begin, the chromosomes, or genetic material, must be copied, which occurs during interphase.
Consider a disease allele that is both dominant and lethal to patients that possess it. How could such an allele be passed on from generation to generation?
The disease must be lethal later in life, after the patient has had children. All dominant lethal disorders, by definition, must strike after childbearing years. If the disorder were lethal to infants, it would never be passed on, as there could be no healthy carriers with a dominant disorder. Huntington disease would be an example of this because it manifests itself later in life, typically after age 40, when people have already had children.
How is it that the entire diversity of life can be spelled out using only four different bases?
The diversity is based on the unique sequence the bases are in. The diversity is based on the unique sequence the bases are in.
Why can't a color-blind father pass this condition on to his sons?
The father gives only his Y chromosome to his sons. The gene for color vision is contained on the X chromosome, which the father never gives to his sons.
A gene is moved from chromosome 12 to chromosome 15. What has happened to this gene?
The gene is in a new locus. Changing the physical position of a gene (such as in a transversion or translocation mutation event) changes the locus of the gene.
Many science fiction books and movies have suggested that human cloning will be a dominant mode of reproduction in the future. Cloning involves making genetically identical individuals from pre-existing genomes. Which of the following presents a good scientific argument against this practice?
The large percentage of species making use of sexual reproduction suggests that maintaining genetic variation is important for the evolutionary success of a species. The benefits of a genetically varied species have been shown to be true time and again. In fact, evidence has shown that genetic variation is more important than total number of individuals to the survival of an endangered species.
Which statement about DNA replication is CORRECT?
The leading strand is built continuously, and the lagging strand is built in pieces. The leading and lagging strands are the new strands of DNA made during DNA replication. The leading strand is built continuously, and the lagging strand is built in pieces.
If a person has two normal copies of the hemoglobin allele, which statements are true?
The person is susceptible to malaria. The person is homozygous at the hemoglobin locus. A person with two copies of any allele is homozygous. A person with two normal copies of the hemoglobin allele is more susceptible to malaria than someone with a sickle cell hemoglobin allele.
In replicating a DNA strand, polymerase makes a mistake and puts adenine across from guanine. If the base-pair mistake is retained, then this could change the shape of the resulting DNA molecule. How might a proofreading enzyme detect this mistake?
The two nucleotides are too large to fit across from each other because of the double-ring base structure. The enzyme will notice the bulge in the DNA structure and attempt to repair the mistake. Properly paired nucleotides create a DNA helix that is uniform in size. This bulge could be caused only by a mutation.
How can we best summarize the role of Watson and Crick in discovering the structure of DNA?
They created a key hypothesis for the structure of DNA. They did not perform experiments themselves; they created a correct hypothesis using data from multiple sources.
During _____ sister chromatids separate.
anaphase II Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.
Which of these phases is the most different between mitosis and meiosis?
anaphase and anaphase I In anaphase, of mitosis sister chromatids separate. In anaphase I, of meiosis, homologous pairs of chromosomes separate.
Match the events in this list with the appropriate stages in the answer: chromatids separate, chromosomes shortening and thickening, nuclear envelope starts to reform, chromosomes in a tug of war.
anaphase, prophase, telophase, metaphase This is the correct order that corresponds with the appropriate stages of mitosis.
There are three major checkpoints that regulate progress of the cell cycle. Which of the following would not be one of the valid checkpoints during the cell cycle?
at the juncture of G1 to G2 This is not a valid checkpoint. DNA synthesis occurs between the two checkpoints, so this is missing a major step during interphase.
What is the genotype of the parent with orange eyes and white skin? (Note: orange eyes are recessive.)
bbgg This result of the cross indicates that both orange eyes and white skin are recessive.
A phenotypic ratio of 9:3:3:1 in the offspring of a cross indicates that _____.
both parents are heterozygous for both genes Such a result indicates that the genes assort independently and that, for each gene, the alleles exhibit a dominant/recessive relationship.
How do cigarettes and radiation cause cancer?
by toxic chemicals (in smoke) or radiation that can damage the DNA in cells Chemicals in cigarettes and the free radicals generated by radiation cause sloppy DNA replication, resulting in mutations.
The ease with which humans travel across the globe is likely to increase _____.
gene flow When people travel or migrate, they take their alleles with them.
All the genes in a population are that population's _____.
gene pool All the alleles of all the genes of a population make up a gene pool.
Mutations are changes in the genetic code that can happen because of environmental factors such as toxins, but sometimes they also happen randomly. Which of the following describes the error rate of mistakes that occur in the replication of DNA under normal circumstances for a given DNA strand?
one mistake per every 100 million base pairs matched Although the number can be as high as one mistake for every 10 billion; because of repair mechanisms the replication rate is remarkably reliable.
Compare prokaryotic cells to eukaryotic cells. Which difference between these two cell types affects cell division the most?
one small chromosome versus numerous large chromosomes. The complexity of mitosis is based mostly off of the need to ensure that each cell gets one copy of each chromosome. Prokaryotes have only one chromosome to copy and sort.
Anaphase II
opposite poles
Through meiotic cell division, eggs are produced in the female _________________.
ovaries
At the end of _____ and cytokinesis there are four haploid cells.
telophase II At the end of telophase II and cytokinesis there are four haploid cells.
An old DNA strand is used as a _____ for the assembly of a new DNA strand.
template An old DNA strand is used as a template for the synthesis of a complementary new strand.
How do mutations affect an organism?
they may cause the development of a disease-causing allele, they may cause the development of a more beneficial allele, and they, in some cases, may have no noticeable affect
Meiosis I produces _____ cells, each of which is _____.
two ... haploid At the end of meiosis I there are two haploid cells.
Sexual and asexual reproduction are seen in many different organisms
-Bacteria and single-celled eukaryotic (Paramecium) organisms reproduce asexually -Some multicellular organisms reproduce asexually -Many plant and fungi reproduce both asexually and sexually -Groves of aspen may reproduce asexually by shoots growing up from the root system of a single parent tree Aspen may also reproduce sexually from seeds
If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the phenotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
1 black : 1 orange The heterozygous black-eyed MendAlien has the genotype Bb. The orange-eyed MendAlien has the genotype bb. The result of this cross is two Bb offspring and two bb offspring. This means that two of the offspring have black eyes and two of the offspring have orange eyes. This 2:2 ratio then reduces to 1:1.
If a diploid organism has a genome consisting of four pairs of chromosomes, it can produce __________ different combinations of maternal and paternal chromosomes (disregarding crossing over).
16 Because there are two possible homologues and 4 chromosomes, 2^4 = 16.
What is/are the possible genotypes of a person with type A blood?
Ao or AA A person that has type A blood may have a genotype of Ao, because A is dominant to the o allele. Type AA can only make A glycoproteins, and this person will also be type A.
Telophase
Chromosomes become less condensed and new nuclear envelopes form
__________________ is the stage of the cell cycle when the cytoplasm and organelles divide into two daughter cells and move apart.
Cytokinesis
Which of the following statements is true about dominant alleles?
Dominant alleles mask the presence of recessive alleles. Dominance has nothing to do with how frequent the allele is; all alleles have a 50/50 chance of being passed on to each offspring.
Which of the following is the correct sequence of stages in the mitotic cell cycle that produces a differentiated cell?
G1, S, G2, M, D G1, S, G2, M, D is the correct sequence of events in the mitotic cell cycle to produce a differentiated cell.
How do the genes in DNA control cell function?
Genes carry the instructions for making proteins. Genes control cells by controlling protein production.
How does Dr. Allison's work provide an example of natural selection in humans?
In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles. In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease. In different environments, natural selection favors different characteristics. In areas with malaria, the reproductive advantages of having one sickle cell allele (and some protection from malaria) kept the allele at high frequencies in the population. In areas without malaria, the reproductive disadvantages from sickle cell disease reduced the allele in populations.
Nucleotide
Made up of a phosphate, base, and sugar
Which of the following is a correct description of meiosis?
Meiosis is one round of DNA replication, before meiosis begins, followed by two rounds of cell division. Meiosis still involves DNA replication and relies on two divisions to reach the haploid number.
Considering all the genetic diseases covered in this chapter, what general conclusion can you draw about genetic diseases?
Most genetic diseases are pleiotropic. Very few diseases have just one symptom. The human body uses the same genes in multiple organs, so multiple organs are affected by any one mutation.
Interphase
Most of the cell's life is spent here, when growth occurs. Cells that are about to divide replicate their DNA
A purple-flowered pea plant self-fertilizes and produces both purple and white offspring. What is its genotype?
Pp This is similar to the F1 cross described in Mendel's work. In this genotype the recessive trait is retained and can be passed on in gametes.
A pea plant with purple flowers (and unknown genotype) is crossed with a pea plant with white flowers. One-half of the offspring have purple flowers, and one-half have white flowers. What are the genotypes of the parent plants?
Pp x pp The white plant is automatically recessive (pp), and the purple plant must be heterozygous (Pp) if any offspring have white flowers. This is also called a test cross.
The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?
Prophase Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the nuclear envelope breaks up.
Meiosis
Prophase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis, Meiosis II
Mitosis
Prophase, Metaphase, Anaphase, Telophase
The synthesis of a new strand begins with the synthesis of a(n) _____.
RNA primer complementary to a preexisting DNA strand The synthesis of a DNA strand begins with the formation of an RNA primer.
In the 1800s, it was commonly believed that the traits of both parents for any feature blended to create the offspring and that the blended trait was passed on. Which of the following observations was most important to Mendel's understanding of genes as unchanged units of information?
Recessive traits can disappear and then reappear in later generations.
When sequencing DNA, scientists usually determine the sequence of only one of the two strands. Why is this?
Sequencing one strand gives you the complementary sequence to the other strand. Unless something very strange is occurring, you can take the sequence of the first strand and determine the second strand by rules of base pairing.
What is the most important reason for sexual reproduction?
Sexual reproduction creates genetically unique individuals. The offspring of sexual reproduction are new individuals with unique genetic combinations. Genetic uniqueness allows a species to adapt better to its changing environment.
During DNA replication, which nucleotide will bind to an A nucleotide in the parental DNA?
T During DNA replication, A binds with T.
What is the complementary strand to the following sequence: ATTGCC . . . ?
TAACGG The A on the first strand would match a T on the complementary strand, and so on.
What is the function of the telomere?
Telomeres are protective caps at the end of the chromosome. These regions prevent loss of DNA during replication.
The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?
Telophase Telophase is the final phase of mitosis, when the chromosomes have arrived at the poles and the nuclear envelopes of the two new cells form.
How do cells fit long pieces of DNA into a compartment as small as the nucleus?
The DNA is wrapped around histones. The DNA is wrapped and coiled like a long extension cord around a cord reel.
Which statement would be accurate in describing the DNA of a prokaryotic organism?
The DNA of a prokaryotic cell is contained in a single, circular chromosome. The DNA of prokaryotic cells is not linear as in eukaryotic chromosomes. It is a single circular chromosome attached to the interior of the plasma membrane.
Consider the Hershey-Chase experiment using viruses that attack bacteria. Normally the virus coats stay outside the bacteria and only inject DNA. How would the experiment have been affected if the entire virus had entered the cells?
The bacteria would have been radioactive whether the viruses contained radioactive phosphate or sulfur. No conclusions could be drawn about genetic material. The experiment relied on one of the two molecules not entering the cell.
In a human female that has Turner syndrome, what would be her sex chromosome constitution (the 23rd pair)?
XO This would be a female that has Turner syndrome.
In a human male that has Klinefelter syndrome, what would be his sex chromosome constitution (the 23rd pair)?
XXY This would be a male with Klinefelter syndrome.
In a human male that has Jacob syndrome, what would be his sex chromosome constitution (the 23rd pair)?
XYY
A(n) __________ is any chromosome other than a sex chromosome.
autosome
A(n) __________ is a virus that infects bacteria.
bacteriophage
In the process known as _________________ a bacterium or other single-celled organism divides in half, producing two identical offspring.
binary fission
In a family pedigree, what does the following symbol stand for? (box that's blue on the left and white on the right)
carrier male This is the symbol (square) for a male who is unaffected by the disease but carries one recessive allele. A carrier female would be written as a half-filled-in circle.
______________ is a pattern of inheritance in which heterozygotes express phenotypes of both of the homozygotes.
codominance
Metaphase II
condense in middle
Meaphase I
condensed in middle
_____________ is the process of generating hypotheses from a well-supported generalization such as a scientific theory.
deductive reasoning
A cross between two individuals with black eyes and green skin which results in an individual with orange eyes and white skin is an example of a _____ cross.
dihybrid The cross is examining two characters.
After DNA replication is completed, _____.
each new DNA double helix consists of one old DNA strand and one new DNA strand DNA replication is semiconservative.
A(n) _____________ consists of all the organisms and their nonliving environment within a given area.
ecosystem
If a mutation in the DNA causes a regulator protein such as myostatin to be ineffective, __________ could explain the result.
enhanced cell growth or replication Myostatin specifically is controlling muscle growth and muscle cell replication.
A female that is planning to become pregnant is concerned about her exposure to environmental mutagens which may have caused DNA mutations. In order for these mutations to become heritable, they must affect the:
her egg cells The gametes are passed to the next generation.
An organism that has two different alleles of a gene for a given character (for example, Yy) is said to be ______________ for that character.
heterozygous
Errors in meiosis, called nondisjunction, can affect the number of sex chromosomes or autosomes in a gamete. When can nondisjunction occur?
meiosis I or meiosis II Nondisjunction can occur in meiosis I or meiosis II.
The equatorial plate of the mitotic spindle is formed during what stage?
metaphase During metaphase, the spindle apparatus becomes well defined and the chromosomes get arranged at the equatorial plate.
____________ is a failure of homologous chromosomes or sister chromatids to separate during cell division.
nondisjunction
DNA is composed of building blocks called _____.
nucleotides DNA is a composed of nucleotide units.
Anaphase I
opposide sides
DNA replication occurs at an unbelievably fast rate. Once replication is complete, we can expect to find a _____ number of mistakes.
small DNA polymerase makes few mistakes.
Prophase I
spread out
A thymine base is replaced by a cytosine in a DNA molecule. What type of mutation is this?
substitution Substitution mutations exchange one base pair for another.
Telphase I and Cytokinesis
two cells start forming
Prophase II
two groups spread out
What is the final result of DNA replication of one chromosome?
two new strands, each bound to a parent strand This means that each cell gets one new strand and one parent strand.
Bacteria are _____________, or single-celled, organisms. In contrast, most fungi, plants, and animals are many-celled, or _____________.
unicellular, multicellular
The pointer is indicating the _____.
viral protein coat The viral protein coat surrounds its genome.
What did Wilkins and Franklin discover?
DNA is a helix with repeating subunits. However, they didn't know that DNA was a double helix or that the subunits were bonded in pairs.
Which of these facts, if he had known them, might have led Mendel to formulate different rules for inheritance?
Genes may be linked on the same chromosome, which can cause them to not separate independently. Mendel may have modified his rule of independent assortment if he had known this.
Who demonstrated that DNA is the genetic material of the T2 phage?
Hershey and Chase Hershey and Chase did a series of classic experiments demonstrating that DNA is the genetic material of the T2 phage.
Compare the cells of a woman's leg muscle to the cells of a baby growing inside her womb. What is the most important difference between them?
The chromosomes in the cells of the woman's leg muscle are genetically identical to the rest of her body. The baby's cells contain only half of the mother's chromosomes; the other half come from the father. A baby is genetically unique from its mother. The cells of a muscle contain the same DNA found in the rest of the body.
All human cells are _________________ (2n) except for gametes, which are _________________ (n).
diploid, haploid
______________ is a pattern of inheritance in which the heterozygous phenotype is intermediate between either of the homozygous phenotypes.
incomplete dominance
A pure-breeding plant with red flowers is crossed with a pure-breeding plant with white flowers. The offspring all have pink flowers. The resulting heterozygote results in an intermediate form, an expression unlike either parent phenotypically. What pattern of inheritance does this involve?
incomplete dominance Here the heterozygote has its own phenotype, halfway between both parental phenotypes.
Which processes lead to most genetic variation in sexually reproducing organisms?
independent orientation of chromosomes in meiosis, random fertilization, and crossing over
Cytokinesis
The cytoplasm divides
What word is used to describe the exact position of a gene on a chromosome?
locus The locus of a gene is its exact position on the chromosome.
Homologous pairs of chromosomes are lined up independently of other such pairs during _____.
metaphase I This describes metaphase I.
During _____ chromosomes align single file along the equator of a haploid cell.
metaphase II Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.
What are the monomers of DNA called?
nucleotides The monomers of DNA are composed of a phosphate group, a deoxyribose carbohydrate, and a base.
When cells experience a mutation in the DNA that controls growth checkpoints, this may result in cancerous cells. What is the name given to genes that are associated with cancer that results from uncontrolled cell division?
oncogenes The term "oncogenes," quite literally means "genes that cause cancer." Mutated oncogenes are often associated with cells that are not responding to normal checkpoints.
A(n) __________ is a diagram showing genetic relationships among a group of individuals, usually with respect to a specific genetic trait.
pedigree
A statement describing an expected observation or outcome of a scientific experiment is known as a(n) _____________.
prediction
A(n) _____________ cell lacks a nucleus. A(n) _____________ cell has a "true" membrane-enclosed nucleus.
prokaryotic, eukaryotic
During _____ a spindle forms in a haploid cell.
prophase II Prophase II is essentially the same as mitotic prophase except that the cells are haploid.
Which type of mutation affects the sequence of multiple nucleotides at one time and occurs between chromosomes rather than only in the double helix of one chromosome?
translocation mutations Translocation mutations occur between chromosomes and not just within the same DNA helix.
Stem cells have two important characteristics: self-renewal, and the ability to differentiate into a variety of cell types ("wildcards")
-Can "self-renew" because they retain the ability to divide, perhaps for the entire life of the organism -Include most of the daughter cells formed by the first few cell divisions of a fertilized egg, as well as a few adult cells -When a stem cell divides, usually one daughter remains a stem cell, thus continuing the line; the other daughter eventually differentiates -Some stem cells in early embryos can produce any of the specialized cell types of the entire body
Cell division is required for growth and development
-Process by which organism's cells grow larger or increase in number is called mitotic cell division -Daughter cells may differentiate, becoming specialized for specific functions -The repeating pattern of divide, grow, differentiate, and then divide again is called the cell cycle -Most multicellular organisms have three categories of cells 1.Stem cells 2.Permanently differentiated cells 3.Other cells capable of dividing
Cell division is required for sexual and asexual reproduction
-Sexual reproduction in eukaryotic organisms occurs when offspring are produced by the fusion of gametes (sperm and eggs) from two adults -reproductive cells undergo a specialized type of cell division called MEIOSIS ("reduction division") -gametes have exactly half the genetic information of their parent cells and reestablish the full genetic complement when they fuse -Asexual reproduction forms offspring from a single parent, without having a sperm fertilize an egg
Some cells other than stem cells are capable of continuing to divide, but typically differentiate into only one or two different cell types
-i.e. Dividing liver cells can only become more liver cells
Permanently differentiated cells differentiate and never divide again
-i.e., most heart and brain cells cannot divide -Once they die, they are gone forever
If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the genotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
0 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) The heterozygous black-eyed MendAlien has the genotype Bb. The orange-eyed MendAlien has the genotype bb. The result of this cross is two Bb offspring and two bb offspring. This 2:2 ratio reduces to 1:1.
Black eyes are dominant to orange eyes, and green skin is dominant to white skin. Sam, a MendAlien with black eyes and green skin, has a parent with orange eyes and white skin. Carole is a MendAlien with orange eyes and white skin. If Sam and Carole wereto mate, the predicted phenotypic ratio of their offspring would be _____.
1 black eyes, green skin : 1 black eyes, white skin : 1 orange eyes, green skin : 1 orange eyes, white skin Sam's genotype is BbGg, and Carole's genotype is bbgg.
In human gamete production there is an average of _____ crossover events per chromosome pair.
2-3 These crossover events increase the genetic variation among gametes.
How many pairs of autosomes do humans have?
22 Humans have 22 pairs of autosomes and one pair of sex chromosomes.
In the laboratory fruit fly, the haploid number is 4 (n = 4). How many different chromosome sets can be produced by one fly, excluding crossing over?
2^4 variations Among each chromosome pair, a choice can be made. This means 2 to the power of n unique combinations exist.
Hershey and Chase used _____ to radioactively label the T2 phage's proteins.
35S Hershey and Chase used radioactive sulfur to label the phage's proteins.
A mother has two X chromosomes. A father has an X and a Y. What are the odds that they produce a female child?
50% Because the father passes an X and a Y at equal frequency, that results in only half of the offspring having XX. In humans, the type of sex chromosome the sperm is carrying when it fertilizes the female egg determines the sex of the child.
Let's consider meiosis in mosquitoes, which have three pairs of homologous chromosomes (n = 3, 2n = 6). At the conclusion of meiotic cell division, a mosquito can produce how many different gametes with unique sets of chromosomes (excluding crossing over).
8 At the conclusion of meiotic cell division, a mosquito can thus produce gametes with any one of eight unique sets of chromosomes.
In some plants there are more than two copies of each homologous chromosome, a condition known as polyploidy. In a hexaploid plant, if the total chromosome count is 48, what is the haploid value (n)?
8 Eight chromosomes times six sets of chromosomes derives the total value of the number of homologous chromosomes in this situation.
Every cell of the body that contains a nucleus has the same exact genetic code in the DNA, yet not all cells are the same. How is a differentiated cell able to make only the proteins it requires for its specific needs?
A cell accesses the portions of the DNA code, that is, genes required to make the proteins that it needs, rather than reading the entire code and making unnecessary proteins. The sequence of the DNA that codes for necessary proteins is the portion accessed by differentiated cells.
Which of these is a testcross?
A? x aa A testcross is used to determine whether an individual expressing the dominant phenotype is homozygous dominant or heterozygous.
Which of these individuals is a homozygous genotype?
AA When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.
You wish to demonstrate that DNA replication is semiconservative. You choose to work with bacteria because they have only a single chromosome. You have a very special device that can measure radiation in individual cells. Which radioactive element or compound should you add to the cells prior to division, and what do you expect to see?
Add radioactive phosphate, and expect each cell to contain a radioactive chromosome. Because replication is semiconservative, each cell should receive a strand of the new, radioactive DNA.
Suppose that every few years, all people over 6 feet tall do not have any children. How will this affect the human population?
Alleles that promote "tallness" will decrease in frequency. A reduction in "tallness" alleles is the change expected as a result of this type of selection.
The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?
Anaphase Sister chromatids separate and start their migration toward opposite poles during anaphase.
What is the most important difference between asexual reproduction and sexual reproduction?
Asexually produced cells are genetically identical (excluding mutational events). Sexual reproduction involves the fusion of gametes resulting in new genetic combinations. Sexual reproduction occurs from the fusion of egg and sperm. Asexual reproduction does not involve gametes.
Which of these gametes contains one or more recombinant chromosomes?
B and C Each of the chromosomes in gametes B and C are composed of material derived from both parents.
Which of these gametes contain one or more recombinant chromosomes?
B, C, F, and G These gametes carry chromosomes produced as a result of crossing over.
The result of the following cross indicates that the genotype of the male (offspring has all flat head)
BB Since all of the offspring have flat headtops, it is reasonable to conclude that the allele for flat headtop is dominant to the wild-type headtop allele.
In the following cross the genotype of the female parent is BbGg. What is the genotype of the male parent? [Hint: B = black eyes, b = orange eyes, G = green skin, g = white skin]
BBGg All of the offspring have black eyes, and there is a 3:1 ratio of skin color.
If a mutation occurred in the gene that codes for making DNA polymerase, disabling the ability of this enzyme to be formed properly, then which of the following effects would you expect to occur in a somatic cell?
Base pairing would not occur during DNA replication, and the creation of the daughter strand would be interrupted. One of the many jobs of the DNA polymerase is to do the base-pair matching using free nucleotides during DNA replication.
Two healthy parents give birth to a child with cystic fibrosis, an autosomal recessive disorder. What can we say about both parents in terms of the genotype and/or phenotype?
Both parents are heterozygous for the disease allele. Both parents must be heterozygous and carry the recessive allele for the child to have received two recessive copies.
Which of the following statements is not associated with meiosis?
Cell division takes place in body (somatic) cells In meiosis, cell division is responsible for producing gametes.
Telophase II and Cytokinesis
Cells form
DNA is compacted and condensed to make it easier to proceed through the cell cycle. What is the correct sequence from loosely compacted DNA to highly condensed DNA?
DNA double helix, histone, chromatin, chromosome This is the correct sequence of components when the DNA is compacted and condensed.
Which of the following is not true about the structure of DNA?
DNA is composed of nucleotides with base pairs that are loosely joined together by covalent bonds. DNA bases are attracted by hydrogen bonds, not covalent bonds.
Which statement about DNA replication is FALSE?
DNA ligase adds nucleotides to the lagging strand. You're right! This statement is FALSE. DNA ligase seals the gaps between segments of DNA in the lagging strand. It does not add nucleotides to the lagging strand.
The molecule that seals the gaps between the pieces of DNA in the lagging strand is
DNA ligase. DNA ligase seals the gaps between the pieces of DNA in the lagging strand, turning it into a continuous strand.
Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
DNA polymerase can assemble DNA only in the 5' to 3' direction Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled in short 5' to 3' segments, which are later joined together by ligase.
Which of the following build(s) new strands of DNA?
DNA polymerases DNA polymerases build new strands of DNA by adding DNA nucleotides one at a time.
Which of the following statements about the daughter cells of prokaryotic fission is true?
Daughter cells are genetically identical to each other. Daughter cells of prokaryotic fission are genetically identical.
How did Dr. Allison test his hypothesis that sickle cell disease was connected to malaria?
He evaluated blood samples for malaria parasites and the presence of sickle cells. He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected. Dr. Allison gathered blood samples from more than 5,000 children in East Africa. He analyzed the samples to identify malaria parasites and sickle cells. He found that children carrying the sickle cell character (or trait) had a lower parasite count, as if they were partially protected against malaria.
In 1949, Dr. Tony Allison observed a high frequency of Kenyans carrying the sickle cell allele in coastal areas and near Lake Victoria, but a lower frequency in the highlands. What did he hypothesize?
He hypothesized that there was a connection between malaria and sickle cell disease. On the basis of this hypothesis, Dr. Allison predicted high frequencies of sickle cell disease only in areas where malaria is common.
The next two generations of the royal family are shown on the expanded pedigree below. Using the pedigree and your knowledge of hemophilia inheritance, determine which predictions can be made about the hemophilia status of future generations.
If Alfonso Crown Prince has children with an unaffected female, all of their daughters would be carriers of the hemophilia allele. If Irene has children with an unaffected male, approximately 50% of their sons would be hemophiliacs. Hemophilia is a recessive and sex-linked disease, which means that the affected allele is carried on the X chromosome. A carrier female would have the hemophilia allele on one of her two X chromosomes. If a carrier female had children with an unaffected male, she would have a 50% chance of passing the hemophilia allele to her daughters and a 50% chance of passing the hemophilia allele to her sons.
In some populations, 1 in 500 people have sickle cell disease. What reason does the film give for why a potentially deadly, inherited disease is found at such high frequencies?
Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population. People with one sickle cell allele are protected from malaria, but do not have sickle cell disease. Protection from malaria comes at the cost of more sickle cell disease in the population.
Stages of Mitosis
Interphase, Prophase, Metaphase, Anaphase, Telophase and Cytokenesis
__________________ is the second phase of mitosis, in which chromosomes line up along the equator of the cells. This phase is followed by anaphase, when sister chromatids separate.
Metaphase
The chromosomes line up in the center of the cell during which phase of mitosis?
Metaphase Metaphase occurs in the middle of mitosis, when the chromosomes line up in the middle of the cell.
Prophase
Microtubules form the mitotic spindle, and the nuclear envelope breaks up
Key Events in Mitosis
Mitotic spindle forming, sister chromatids centered, chromosomes separating, nuclear envelopes forming
Mules are the hybrid offspring of a cross between a horse and a donkey, two distinctive species with different chromosome counts. Why are mules virtually always sterile?
Mules have an odd set of chromosomes (63), thus preventing proper alignment of homologous chromosome lineup in meiosis I. Important genes will be missing in the gametes produced, resulting in lack of reproductive success because fertilized eggs will be unable to continue development. Correct, this is an issue with meiosis. Mules may have the ability and drive to mate, but their offspring will be unsuccessful and likely never be born because of chromosome count issues and missing genes.
Which of the following sentences uses the words "chiasma," "recombination," and "crossing over" correctly?
Recombination occurs when homologous chromosomes with different alleles exchange DNA by crossing over at a point called a chiasma. Remember that different alleles must be involved before crossing over can be called recombination, which generates new combinations of alleles on the resulting chromosome.
Which of these phases of the cell cycle is most similar between a cell that will divide by mitosis and one that will divide by meiosis?
S phase In either case, the DNA must be duplicated to divide the cells.
Centrioles duplicate during the cell cycle. Given your knowledge of the cell cycle, when would you guess that the duplication of centrioles occurs?
S phase Soon after the cell makes the decision to divide, the centrioles are duplicated along with the chromosomes during the S phase.
Compare sickle cell disease and malaria.
Sickle cell disease and malaria are both potentially lethal diseases. Though malaria is an infectious disease and sickle cell disease is inherited, both can cause life-threatening conditions.
Anaphase
Sister chromatids separate and become full-fledged chromosomes that move to opposite poles
Gene duplication is a type of mutation where one gene is copied to a second location within the genome. The original location still contains the same gene, but now there are two locations with the gene. Evidence shows that this event has happened many times throughout the evolution of life. Why might gene duplication be advantageous to an organism undergoing adaptation?
The second gene can be mutated to new functions without losing the function of the original gene. This creates new and unnecessary material that can be mutated with little penalty.
Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.
The sickle cell allele will decrease in frequency. Without malaria, selection for the sickle cell allele decreases. As a result, the frequency will likely decrease.
A person is heterozygous for hair texture. Which of these statements is correct about this person's DNA?
This person has two different alleles at the locus for hair texture. Heterozygotes for a particular trait carry two different alleles.
How many major checkpoints are there in the cell cycle that regulates the progress of the cell cycle?
Three They are at the juncture of G1 to S, at the juncture of G2 to mitosis, and between metaphase and anaphase.
Stem cells have two important characteristics: self-renewal and the ability to differentiate into a variety of cell types ("wildcards"). Which of the statements below would not be a valid characteristic of stem cells?
When a stem cell divides, both resulting daughter cells become stem cells, thus continuing the line. This is not a correct statement for stems cells. When a stem cell divides, usually one daughter remains a stem cell, thus continuing the line while the other daughter eventually differentiates.
Which of the following would indicate a base pairing mutation in DNA?
a G paired with a T G and T should not pair.
On the molecular level, what exactly is a mutation?
a change in the sequence of DNA bases The information in DNA is contained in the base sequence, so if this is changed, the information is changed.
In agriculture there are numerous strains of crops that are considered "hybrids," which are intentionally selected for a specific trait that is considered desirable such as a preferred height or color. In genetics, which of the following is consistent with how a genetics researcher would use this word?
a cross-fertilization where the contributing parents differ in at least one genetically determined trait Correct, in this case the hybrid is synonymous with heterozygous. The desired trait is typically dominant.
Which of the following is most likely to be passed on to the next generation (i.e., parent to offspring)?
a mutation in the DNA in cells in the ovaries Eggs in females are produced by the specialized division process called meiosis, which takes place in the ovaries. If the DNA of the ovaries is mutated, the egg will be mutated as well.
Which of the following is the most important for generating the most genetic variability in a species?
ability to fuse haploid gametes from separate parents to form a new individual, that is, form a diploid individual with two sets of homologous chromosomes The ability to combine different sets of alleles into one individual is most important to generating diversity.
At a very low frequency, the single-ringed pyrimidine cytosine can spontaneously lose its amino group (NH2) and form the base shown. Which nucleotide will this deaminated cytosine pair with?
adenine The pattern of charges matches very closely with thymine, so this nucleotide will pair with adenine when replication occurs.
The result of the following cross indicates that the genotype of the female (offspring has all flat head)
bb The result of this cross indicates that the flat headtop allele is dominant to the wild-type headtop. Thus, the only way to express a wild-type headtop is to be homozygous recessive.
In order to determine the genotype of a MendAlien with black eyes and green skin, you would cross this individual with a(n) _____ individual.
bbgg This is an extension of the single character testcross you worked with in the activity on monohybrid crosses.
_____________ is the study of living things.
biology
Which cellular structure contributes to the biggest difference between mitosis in plants and mitosis in animals?
cell wall The cell wall of plants is rigid, preventing the cell from being pinched in half by a microfilament belt.
Which of the following components related to chromosome anatomy connect two sister chromatids after DNA replication?
centromere The role of the centromere is to attach the two sister chromatids, after DNA replication, often near the middle portion of the chromatids.
Which specific structure must separate during anaphase for sister chromatids to begin moving toward opposite poles?
centromeres
A(n) ________________ consists of a very long DNA molecule associated with many proteins. During the cell cycle, this structure is duplicated and the copies are distributed to separate cells.
chromosome
Prokaryotic fission would not occur if which of the following items or processes were missing or not completed properly?
chromosome duplication All other things in the cell can be replaced, but the DNA must be duplicated or one of the daughter cells will be useless.
What is a test cross in the context of Mendelian genetics?
crossing an organism with a dominant phenotype (and unknown genotype) with one that has a recessive phenotype This is the easiest way to determine whether the organism with the dominant phenotype is homozygous or heterozygous.
Which of the following is produced in response to growth factors binding to surface receptors?
cyclins Cyclins are produced after surface receptors bind growth factors.
At the end of the mitotic (M) phase, the cytoplasm divides in a process called _________________.
cytokinesis Cytokinesis is the division of the cytoplasm that occurs in conjunction with telophase, the last phase in mitosis.
UV rays can strike two thymine bases sitting beside each other on the same strand, causing them to become linked tightly to one another. This pulls the thymines closer together, altering the spacing of the nucleotides. What kind of error during replication is this likely to cause?
deletion Polymerase is likely to put only a single adenine across from one of the thymines and skip the other due to the altered spacing.
In diploid life cycles of most animals, the majority of the cycle is spent as what type of cell?
diploid In most animals, virtually the entire diploid life cycle is spent in the diploid state.
DNA has the appearance of a _____.
double helix Eukaryotic DNA is organized as a double helix.
Which of the following factors of genetic recombination occurs after meiosis I?
fertilization Genetic recombination from fertilization from the union of two haploid gametes creates a situation of a totally unique individual.
Meiosis II typically produces _____ cells, each of which is _____.
four ... haploid At the end of meiosis II there are typically 4 haploid cells.
Meiosis starts with a single diploid cell and produces View Available Hint(s)
four haploid cells
The enzyme DNA __________ helps unwind the DNA double helix during DNA replication.
helicase
The first step in the replication of DNA is catalyzed by _____.
helicase The first step of DNA replication is unwinding the DNA double helix.
__________ is a recessive sex-linked disorder in which the blood fails to clot normally.
hemophilia
____________ is a recessive sex-linked disorder in which the blood fails to clot normally.
hemophilia
Considering pea flowers, where purple is dominant to white, describe the genotype of a plant with the alleles Pp.
heterozygous A heterozygous plant is one with two different alleles for a particular gene.
The proteins that coil with DNA producing the "beads on a string," or nucleosomes, are called which of the following?
histones These are the specialized proteins that the DNA will wrap around to assist in the compacting.
Diploid cells have matched pairs of chromosomes, called _________________ chromosomes. One member of each pair is inherited from the father, the other from the mother.
homologous
Which of the following are separated during anaphase I?
homologous chromosomes Homologous chromosomes are separated in anaphase I, and sister chromatids are separated in anaphase II (when they split at the location of the centromere).
During prophase I of meiosis,
homologous chromosomes stick together in pairs. Homologous chromosomes stick together in pairs during prophase I.
An organism that has two identical alleles of a gene for a given character (for example, YY or yy) is said to be ______________ for that character.
homozygous
In pea plants, purple flower color is dominant to white flower color. Describe the genotype of a white flower.
homozygous recessive
Which of the following is most responsible for DNA forming a double helix instead of a single-strand helix structure?
hydrogen bonding between bases The hydrogen bonds between bases hold the two DNA strands together to form a double helix.
__________________ is the stage of the cell cycle between cell divisions, in which the cell acquires nutrients, grows, and duplicates its chromosomes.
interphase
A cell preparing to undergo meiosis duplicates its chromosomes during
interphase Chromosomes are duplicated during interphase.
A chromosomal __________ occurs when a chromosomal fragment breaks off and reattaches to the chromosome in a flipped orientation.
inverison
After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that theycontained _____, which demonstrated that _____ is the phage's genetic material.
labeled DNA ... DNA Since the phage DNA entered the infected cell, it makes sense that DNA is the genetic material.
During which stage of mitosis is the nuclear membrane broken into fragments?
late prophase During late prophase, the nuclear membrane is broken into fragments.
The enzyme DNA __________ creates a continuous single strand of DNA by bonding the terminal sugar in one DNA fragment to the terminal phosphate in another fragment.
ligase
Short segments of newly synthesized DNA are joined into a continuous strand by _____.
ligase Ligase joins DNA segments into a continuous strand.
Which of the following represents an exception to the law of independent assortment?
linkage Two genes that are linked on the same chromosome do not assort independently.
Of the following cell types which is not considered to be in the category of permanently differentiated cells?
liver cells Liver cells that are differentiated still have the capacity to divide to replace damaged liver cells.
What is the definition of cross-fertilization in Mendel's pea plant experiments?
mating two plants to produce offspring Cross-fertilization just means that offspring are the result of two parents. Self-fertilization is the opposite.
The process of _________________ reduces the number of chromosomes in a diploid cell by half, producing four haploid cells.
meiosis
The overall process of nuclear division is known as __________________
mitosis
When three or more alleles of the same gene exist in a population (as with human blood types), they are known as ______________.
multiple alleles
Crossing over, resulting in an increase in genetic variation, occurs between _____.
nonsister chromatids of homologous chromosomes This process produces chromosomes containing genes inherited from both parents.
What type of mutation occurs, during replication, when a base pair is mismatched and a wrong base is placed into the daughter strand, for example, when C is paired with C?
nucleotide substitution Exchanging one base pairing for another is a nucleotide substitution change.
What are the basic building blocks that are used to construct a gene?
nucleotides A gene is a string of nucleotides. Most genes are hundreds or thousands of nucleotides long.
A(n) ____________ is a diagram showing genetic relationships among a group of individuals, usually with respect to a specific genetic trait.
pedigree
This is an image of a _____. (creepy spider looking thing)
phage This is a T2 phage, a type of phage that infects E. coli.
An organism's traits--including its outward appearance, behavior, and other observable or measurable features--is known as its ______________.
phenotype
__________ is a situation in which a single gene influences more than one phenotypic characteristic.
pleiotropy
The enzyme DNA __________ synthezises new DNA strands by matching bases on a preexisting template strand with complementary free nucleotides and bonding them together.
plymerase
In __________ inheritance, the interactions of two or more functionally similar genes determine inheritance.
polygenic
______________ is a form of inheritance in which the interaction of multiple genes contributes to a single phenotype, such as skin color.
polygenic inheritance
__________________ is the first phase of mitosis, in which chromosomes condense and spindle microtubules begin to form.
prophase
Synapsis occurs during _____.
prophase I Synapsis, the pairing of homologous chromosomes, occurs during prophase I.
Major gene reshuffling takes place during what phase of meiosis?
prophase I This is the stage at which crossing over takes place.
The correct order of events during meiosis is
prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II.
During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?
prophase I. Segments of nonsister chromatids trade places during prophase I, resulting in recombination.
The result of the following cross indicates the orange eyes are _____ black
recessive to The result of this cross indicates that both parents are heterozygous for eye color.
Crossing over results in _________ -- the formation of new combinations of different alleles on a chromosome.
recombination
Crossing over results in ____________ -- the formation of new combinations of different alleles on a chromosome.
recombination
The action of helicase creates _____.
replication forks and replication bubbles A replication fork is the transition region between paired and unpaired DNA strands.
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium The bacterium ruptures and phages are released.
The process of DNA replication is __________ , meaning tat it conserves one parental DNA strand and produces one newly synthesized strand.
semiconservative
Natural selection can enhance the frequency of beneficial mutations in a population. In which type of cells must the mutations occur to have an effect on future generations?
sex cells/gametes If the mutation occurs in sperm or eggs, the mutation can be passed on assuming reproduction occurs. If reproduction does not occur, any beneficial mutations will not be passed on to subsequent generations.
Which of the following functions would not use the process of mitosis?
sexual reproduction Sexual reproduction would use the process of meiosis, not mitosis.
What forms the backbone of a DNA molecule?
sugar rings and phosphates All DNA molecules, regardless of their sequence of bases, have the same sugar and phosphate backbone.
__________________ is the final stage of mitosis, in which spindle fibers disappear and cytokinesis occurs.
telophase
Which phase of mitosis comes last during cell division?
telophase Cytokinesis is part of M phase, but not part of mitosis. M phase consists of nuclear division (mitosis) and cytoplasmic division (cytokinesis). Telophase is part of mitosis, so it's in M phase too.
At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
telophase I At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.
Which of the following components or tests is unnecessary when evaluating a gene with incomplete dominant inheritance?
test cross A test cross is specifically used to determine whether an individual with the dominant phenotype is a homozygote (i.e., "RR") or a heterozygote (i.e., "Rr"). Genes that show incomplete dominance have a different phenotype for the heterozygote, so this test is unnecessary.
As a result of the lytic cycle, _____.
the host cell's DNA is destroyed The host cell's DNA is destroyed, and ultimately, the host cell itself is destroyed in the lytic cycle.
If a cell was unable to properly manufacture cyclins or Cdks, which of the following processes would most directly be affected and unable to proceed?
the initiation of DNA replication during interphase The initiation of S phase is under regulation of cyclins and their associated Cdks.
What feature controls how tightly linked two genes are?
the physical distance between the two genes Genes that are physically close to each other on the same chromosome are more tightly linked than genes that are physically far apart.
Genetic drift is a process based on _____.
the role of chance Genetic drift requires a small sample size.
In mitosis, the number of chromosome sets in daughter cells is which of the following?
the same as in the parent cell There is the same number of chromosome sets in daughter cells as in parent cells.
A mutation occurs when _____.
there is a change in the DNA sequence of a gene This is the definition of mutation.
In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.
thymine ... cytosine This is referred to as specific base pairing.
A chromosomal __________ occurs when two nonhomologous chromosomes exchange pieces, leaving each with improper gene sequences.
translocation
Down syndrome is also called ____________ 21 because the cells of affected individuals contain three copies of chromosome 21.
trisomy