8/9
translocation
(1) During protein synthesis, the movement of a tRNA molecule carrying a growing polypeptide chain from the A site to the P site on a ribosome. (The mRNA travels with it.) (2) A change in a chromosome resulting from a chromosomal fragment attaching to a nonhomologous chromosome; can occur as a result of an error in meiosis or from mutagenesis.
During anaphase II, _____.
sister chromatids separate and migrate toward opposite poles
An example of a cell that is 2n is a __________.
somatic cell
An example of a cell that is 2n is a(n) _____.
somatic cell
Mitosis occurs in _____; meiosis occurs in _____.
somatic or body cells ... germ cells in the testes or ovaries
Looking through a light microscope at a dividing cell, you see two separate groups of chromosomes on opposite ends of the cell. New nuclear envelopes are taking shape around each group. The chromosomes then begin to disappear as they unwind. You are witnessing ______.
telophase
At a critical point in meiosis, the chromosomes do not replicate. This occurs between _____.
telophase I and prophase II
Since there is a genetic explanation for short sleepers, you would expect
that this trait appears more frequently among family members.
DNA replication occurs in _____.
the S phase of interphase
A large and increasing number of genetic tests are available to prospective parents and children. Even as these testing methods become more and more sophisticated, what is one thing technology will never solve?
the ability to prescribe the correct course of action based on test results
One event occurring during prophase is _____.
the beginning of the formation of the mitotic spindle
Crossing over is _____.
the exchange of homologous portions of nonsister chromatids
Hemophilia appears rarely in females. This is because _____.
the female must possess the hemophilia gene on both X chromosomes
Cystic fibrosis is inherited in an autosomal recessive pattern. Males who have cystic fibrosis are usually sterile. Furthermore, the disease is often lethal before the age of reproduction. Even though people with the disease rarely reproduce, cases continue to arise because __________.
the harmful allele "hides" inside heterozygous individuals and one-fourth of the offspring of two heterozygotes should be afflicted
Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Even though people with the disease rarely reproduce, cases continue to arise because _____.
the harmful allele "hides" inside heterozygous individuals and one-fourth of the offspring of two heterozygotes should be afflicted
In a monohybrid cross, F2 refers to __________.
the second filial generation, or the "grandchildren" of the original mating pair
The discovery of a gene associated with short sleepers means that
there is potential to manipulate sleep pathways with medication.
During mitosis, the chromosomes move because _____.
they attach to a dynamic, precisely regulated mitotic spindle
Individual chromosome placement is usually observed with a light microscope during mitosis, even though cells spend more time in interphase. This is because _____.
they have uncoiled to form long, thin strands
Meiosis is typically accomplished in _____.
three steps. All of the chromosomes are duplicated in a diploid cell, and then there are two cell divisions to produce a total of four haploid gametes.
As we now understand it, the Law of Independent Assortment applies _____.
to pairs of genes that are on different chromosomes, but NOT to pairs of genes that are close together on the same chromosome
The major contribution of sex to evolution has been _____.
to provide a method that creates greater genetic variation
Mitosis and cytokinesis result in the formation of _____; meiosis and cytokinesis result in the formation of _____.
two diploid cells ... four haploid cells
At the end of telophase I of meiosis, as cytokinesis occurs, there are _____.
two haploid cells
Mendel's view of the mechanism of heredity was radically different from the prevailing view of the time because he saw heredity working through _____.
unchanging (immutable), heritable factors that were contributed by each parent and never mixed
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 crossed with a short plant. Half the offspring are tall, and half are short. This allows us to conclude that the tall plant _____.
was heterozygous
In Labrador retrievers, a common breed of dogs, black coat is dominant to chocolate, normal vision is dominant to progressive retinal atrophy (PRA), and normal hip joint is dominant to hip dysplasia. All these genes assort independently. Two dogs that are heterozygous for alleles of all three genes are crossed. Using rules of probability (not a Punnett square), what is the chance that the first pup born to these dogs will be chocolate, have normal vision, and have normal hip joints?
9/64
A human bone marrow cell in the prophase stage of mitosis contains 46 chromosomes. Therefore, there are a total of __________ sister chromatids in this cell.
92
A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. There are _____ chromatids.
92
Imagine that a human skin cell went through mitosis but did not undergo cytokinesis. How many chromosomes would be in the cell?
92
inversion
A change in a chromosome resulting from reattachment of a chromosome fragment to the original chromosome, but in the reverse direction. Mutagens and errors during meiosis can cause inversions.
cell cycle control system
A cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle.
Your uncle has prostate cancer. Which of the following indicates improvement in his condition?
A decreasing PSA
cancer
A disease characterized by the presence of malignant tumors (rapidly growing and spreading masses of abnormal body cells) in the body.
karyotype
A display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere position. Karyotypes may be used to identify certain chromosomal abnormalities.
cell plate
A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.
mitotic spindle
A football-shaped structure formed of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis and meiosis.
Chromosomes
A gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell. A chromosome consists of one very long DNA molecule and associated proteins.
trisomy 21
A human genetic disorder resulting from the presence of an extra chromosome 21; characterized by heart and respiratory defects and varying degrees of mental retardation.
binary fission
A means of asexual reproduction in which a parent organism, often a single cell, divides into two genetically identical individuals of about equal size.
Achondroplasia is a common cause of dwarfism and is an autosomal dominant condition. If a male individual has achondroplasia, which statement below must be true?
At least one of this man's parents must have shown signs of dwarfism.
What is the difference between a benign tumor and a malignant tumor?
Benign tumors do not metastasize; malignant tumors do.
Which of the following is true?
Both women and men can be carriers for genetic disorders.
In lentils, the C gene has two different alleles. CSCS homozygotes have spotted seeds, CDCD homozygotes have dotted seeds, and CSCD heterozygotes have seeds with both spots and dots. This indicates that _____.
CS and CD are codominant
In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?
Cancer cells continuously secrete growth factors into the cell culture medium.
Which of the following occurs during mitosis?
Chromatids separate. Two daughter nuclei, one at each pole of the cell, are generated.
An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype _____.
EEGgcc
Two normal parents have three normal children: one son and two daughters. Their son and one of their daughters marry and also have normal children. Their second daughter, Mary, marries a man with a rare, recessive blood disorder. They have two children, and both children develop the blood disorder. What were the genotypes of Mary's parents?
Either one of her parents or both of her parents were heterozygous for the trait.
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.
Consider the cell cycle shown below. Cells will usually divide if they receive the proper signal at a checkpoint in the _____ phase of the cell cycle.
G1
When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. This observation can be explained if this cell's cell cycle halted at checkpoint _____.
G1
Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct cell cycle sequence of events for these reactivated cells?
G1, S, G2, M
Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct sequence of events?
G1, S, G2, M
The chromosome theory of inheritance is based upon which of the following sets of observations?
Genes segregate; chromosomes come in pairs.
Which of the following is a leading cause of sudden death among young athletes?
HCM
A couple who both have the ability to roll their tongues have a son who is also a tongue-roller. Tongue-rolling is a dominant characteristic. The son is curious about whether he is homozygous or heterozygous for tongue-rolling. How could he find out?
Have children with a woman who is a non-roller. If any of their children is a non-roller, then he is heterozygous for the trait.
Two individuals decide to have children. The expected blood group genotypes are 50% of blood type A, and 25% each of blood types AB and B. What genotypes are the parents?
IA i x IA IB
Two individuals decide to have children. The expected blood group genotypes are 50% of blood type A, and 25% each of blood types AB and B. What genotypes are the parents?
IAi x IAIB
meiosis
In a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter nuclei. Meiosis and cytokinesis produce haploid gametes from diploid cells in the reproductive organs of the parents.
diploid
In an organism that reproduces sexually, a cell containing two homologous sets of chromosomes, one set inherited from each parent; a 2n cell.
haploid
In the life cycle of an organism that reproduces sexually, a cell containing a single set of chromosomes; an n cell.
You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?
In trisomy there would be one extra chromosome; in a duplication, the number of chromosomes would be normal, but one chromosome would have two copies of a portion of the chromosome.
In breeding pure-breeding large and small strains of mice, you cross individuals of each strain and note that their offspring are intermediate in size. Two models (explanations) to account for this result are (1) that body size in these strains is due to one gene with alleles that show incomplete dominance and (2) that body size is a polygenic trait. How could you distinguish between these models?
Intercross the F1 and see if the F2 contains three size classes (consistent with the incomplete dominance model) or if there is a range of sizes (consistent with the polygenic model).
During binary fission, each copy of the duplicating chromosome moves to opposite ends of the cell. What does this achieve?
It ensures that each daughter cell receives one copy of the chromosome.
During binary fission, one copy of the duplicating chromosome moves to the opposite end of the cell. What does this achieve?
It ensures that each daughter cell receives one copy of the chromosome.
You cross two fruit trees. One tree produces lemons with spiky leaves. The other produces limes with smooth leaves. Your F1 generation produces lemons with smooth leaves and spiky leaves. What are the genotypes of the parents? L = lemons; l = limes; S = smooth leaf; s = spiky leaf.
LLss and llSs
Why are lethal dominant alleles so much more rare than lethal recessive alleles?
Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles.
Akin to urban legends, there are curious genetics legends—things like eye color being determined by one gene, with a brown eye allele being completely dominant to blue. The problem comes when simple myth meets the complex reality of how eye color and many other traits are transmitted. Why is the inheritance of so many traits difficult to explain using only Mendel's view of genetics?
Mendel was correct for the traits he investigated, but his principles must be extended (not discarded) to explain many more complex patterns of inheritance.
Which of the following is a correct representation of an event that occurs in mitosis?
Metaphase—chromosomes line up on the equatorial plane.
In an individual of genotype Aa, where are the A and a alleles physically located?
One allele is on one chromosome, and the other is in the same position (locus) on the homologous chromosome.
sister chromatid
One of the two identical parts of a duplicated chromosome in a eukaryotic cell. Prior to mitosis, sister chromatids remain attached to each another at the centromere.
Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the X chromosome is not. What is the explanation for this difference?
Only one copy of the X chromosome is functional, regardless of the total number of X chromosomes.
How have Mendel's laws fared as we have learned more about cell biology and processes such as meiosis?
Our new knowledge has helped to explain some of the exceptions to Mendel's laws of inheritance.
Imagine a particular character (such as flower color) that is determined by a single gene. If this gene is present in two forms, how can you tell which allele is dominant and which is recessive?
Perform a cross between two true-breeding individuals and observe the trait or traits expressed by the F1 individuals.
Suppose we have a pea plant with purple flowers, determined by the dominant allele P. How might you determine whether the plant is homozygous (PP) or heterozygous (Pp)?
Perform a testcross: Cross the plant with a white one, which must be homozygous recessive (pp).
Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr x PpRr will have white flowers and wrinkled seeds?
1/16
In a standard monohybrid cross between purple-flowered and white-flowered peas, what fraction of the purple-flowered peas in the F2 generation would you expect to be true-breeding?
1/3
Assume that in cattle a spotted coat is dominant to an even coat, short horns are dominant to long horns, and the traits for coat type and horn length assort independently. In a cross between cattle that are each heterozygous for both traits, what proportion of their offspring are expected to have long horns?
1/4
Hypercholesterolemia is a disorder in which blood cholesterol levels are elevated. The H allele is incompletely dominant to the h allele, with hh homozygotes having extremely high levels of blood cholesterol. A husband and wife are both Hh heterozygotes. What is the chance that their first child will have normal levels of blood cholesterol?
1/4
A cross is made between two heterozygous pea plants, and observations are made about three characteristics: flower color, seed color, and seed shape. What is the probability that the offspring will be heterozygous for all three characteristics?
1/8
If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?
10,000
A cell biologist carefully measured the quantity of DNA in grasshopper cells growing in cell culture. Cells examined during the G2 phase of the cell cycle contained 200 units of DNA. What would be the amount of DNA in one of the grasshopper daughter cells?
100 units
Vitamin D-resistant rickets is an X-linked dominant bone disorder. A man with this form of rickets marries a normal woman. What proportion of the couple's daughters is expected to have vitamin D-resistant rickets?
100%
There are over 100 alleles known for the gene associated with cystic fibrosis. With current technology, it is possible to determine exactly which allele or alleles is/are carried by a person. What is the maximum number of different alleles that any person can carry?
2
How many pairs of autosomes do humans have?
22
Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder that causes urine to turn black when exposed to air. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is _____.
25%
Flower color in snapdragons is an example of incomplete dominance. If a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with another pink-flowered plant, the expected progeny plants will be __________.
25% red, 50% pink, and 25% white
In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing _____ different gametes.
2^23
In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes.
2^23
An AABb individual is mated with another AABb individual. The possible number of genetically different kinds of offspring is _____.
3
How many loci are shown on the homologous chromosomes in the figure below?
3
An organism has a haploid chromosome number n = 4. How many tetrads will form during meiosis?
4
A human somatic cell contains _____ chromosomes.
46
Each cell in an individual with Down syndrome contains _____ chromosomes.
47
In a cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing _____ chromosomes.
5
Huntington's disease is caused by an autosomal dominant allele. If a heterozygous male were to marry a female not carrying the disease, what percentage of the offspring will have Huntington's?
50%
Shown in the figure below are a number of traits that are found in humans to be either dominant or recessive. A woman with freckles has children with a man who has no freckles. Their first child has no freckles. What is the probability of her having a child with freckles with the same man?
50%
A woman who is a carrier of hemophilia marries a man affected with hemophilia. What percentage of their sons and daughters is expected to have hemophilia?
50% of sons and 50% of daughters
Snapdragons show incomplete dominance in their flowers. A pink snapdragon is crossed with a red snapdragon. What color(s) are the offspring?
50% red, 50% pink
Which events occur during prophase?
The nuclear envelope breaks down, Chromosomes condense and are attached to spindle fibers.
Imagine that a mutant strain of Drosophila undergoes crossing over at half the normal rate. How would a genetic map prepared for this mutant differ from a genetic map prepared for a normal (wild type) fly?
The order of genes would be the same in both strains, but the distances measured between genes in the mutant would be half those of the wild type.
The M phase of mitosis and M phase of meiosis both occur after interphase. However, the two processes differ in the arrangement and behavior of their chromosomes. How?
The pairing up of homologous chromosomes and crossing over only occur during meiosis.
What is indicated when a single-character testcross yields offspring in a 1:1 phenotypic ratio?
The parent with the dominant phenotype was heterozygous.
mitotic phase (M phase)
The part of the cell cycle when the nucleus divides (via mitosis), its chromosomes are distributed to the daughter nuclei, and the cytoplasm divides (via cytokinesis), producing two daughter cells.
You are an oncologist. A patient presents with advanced prostate cancer and you follow standard protocol. What do you do?
The patient is treated with chemical castration.
interphase
The period in the eukaryotic cell cycle when the cell is not actually dividing. Interphase constitutes the majority of the time spent in the cell cycle. See also mitotic phase (M phase).
genetic recombination
The production, by crossing over and/or independent assortment of chromosomes during meiosis, of offspring with allele combinations different from those in the parents. The term may also be used more specifically to mean the production by crossing over of eukaryotic or prokaryotic chromosomes with gene combinations different from those in the original chromosomes.
centromere
The region of a duplicated chromosome where two sister chromatids are joined (often appearing as a narrow "waist") and where spindle microtubules attach during mitosis and meiosis. The centromere divides at the onset of anaphase during mitosis and anaphase II during meiosis.
Cell Division
The reproduction of a cell through duplication of the genome and division of the cytoplasm
anchorage dependence
The requirement that to divide, a cell must be attached to a solid surface.
prometaphase
The second stage of mitosis, during which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids.
Within one chromosome, what is the relationship between the sequence of bases in DNA of one sister chromatid compared to the other?
The sequences are identical.
When two average-height parents give birth to a child exhibiting achondroplastic dwarfism, it is most likely due to a new mutation. This is because _____.
achondroplasia is caused by an allele that is always expressed, so the parents couldn't have the allele
Previously, it was thought that the blending hypothesis explained inheritance. The blending hypothesis maintained that _____.
after a mating, genes of the two parents are mixed in the offspring and lose their individual identities
Assume tall (T) is dominant to dwarf (t). If a homozygous dominant true-breeding individual is crossed with a homozygous true-breeding dwarf, the offspring will _____.
all be tall
If a homozygous dominant (AA) is crossed with a homozygous recessive (aa) for a given character, the offspring will be _____.
all of the dominant phenotype
Crossing over is important because it _____.
allows the exchange of genes between homologous chromosomes
Fetal cells may be removed along with fluid from the womb by a process known as _____.
amniocentesis
What is an allele?
an alternative version of a gene
While it is estimated that less than 5% of the population are short sleepers,
an estimated 30% of the population sleep only 6 hours per night or less.
If a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction, the resulting chromosomal abnormality is called _____.
an inversion
Unless the chromosomes were stained to show band patterns, a karyotype would usually be unable to show _____.
an inversion
The phase of mitosis during which the chromosomes move toward separate poles of the cell is _____.
anaphase
Single sister chromatids are found in cells at mitotic _____.
anaphase and telophase
The function of mitosis is to produce daughter cells that _____.
are genetically identical to the parent cell (assuming no mutation has occurred)
In many organisms, including humans, chromosomes are found in homologous pairs. Homologous chromosomes _____.
are identical in the arrangement of their genes, but some versions of the genes may differ between the chromosomes
Human genetic disorders _____.
are most often recessive
The kinetochores _____.
are sites at which microtubules attach to chromosomes
In sexually reproducing multicellular organisms, the main functions of mitosis are ______.
b and c, but not a
A cell replicates its entire chromosomal DNA only _____.
before it is about to divide
In the picture below, the chromosomal region where the nonsister chromatids are crossing over is called a(n) _____.
chiasma
Most of an organism's DNA is carried by its _____.
chromosomes
Homologous pairs of chromosomes frequently _____.
contain different alleles
Meiosis differs from mitosis in that _____ only occurs in meiosis.
crossing over
A cleavage furrow forms in an animal cell during _____.
cytokinesis
A cell is treated with a drug that prevents the formation of vesicles. Which of the following processes depends on the formation of vesicles and would therefore be blocked?
cytokinesis in a plant cell
Meiosis starts with _____ cells and produces _____ gametes.
diploid ... haploid
In bacterial cells, binary fission involves _____.
distribution of a copy of the single parental chromosome to each daughter cell
In bacterial cells, binary fission involves __________.
distribution of a copy of the single parental chromosome to each daughter cell
Cytokinesis refers to _____.
division of the cell outside the nuclear material
Observations of cancer cells in culture support the hypothesis that cancer cells _____.
do not exhibit density-dependent inhibition
Chromatids form _____.
during the S phase
The diploid phase of the human life cycle begins with _____.
fertilization
Cytokinesis _____.
finishes mitosis by diving the cytoplasm and organelles of the original parent cell into two separate daughter cells.
How long can sperm be cryogenically stored and still be viable?
for more than 20 years
Cytochalasin B is a chemical that disrupts microfilament formation. This chemical would interfere with _____.
formation of a cleavage furrow
Consider the photograph shown below. You can determine this is a plant cell rather than an animal cell because it has _____.
formed a cell plate
The function of meiosis is to make _____.
four cells with a haploid number of chromosomes
What is the typical result when a diploid cell undergoes meiosis?
four haploid cells
In sexually reproducing multicellular organisms, the main functions of mitosis are _____.
growth and development; tissue repair/replacement of damaged cells
At the conclusion of meiosis I, the daughter cells are _____.
haploid and the sister chromatids are joined
Fertilization joins _____ to produce a _____.
haploid gametes ... diploid zygote
The results of a testcross (that is, the offspring of this cross) were 50% phenotypically dominant and 50% phenotypically recessive. The genotype of the phenotypically dominant parent in this cross was _____.
heterozygous
Consider the two mice shown below. They have the same chromosomes, carrying genes for the same traits in the same loci, but specifying different versions of the same traits—for example, coat and eye color. These chromosomes are called _____.
homologous chromosomes
Mendel observed that pairs of alleles were separated or segregated in gametes and that they were rejoined in fertilization. We know that pairs of _____ are segregated in _____ and then are rejoined through fertilization.
homologous chromosomes ... meiosis
The _____ separate in meiosis I; the _____ separate in meiosis II.
homologous chromosomes ... sister chromatids
In anaphase I, _____.
homologous chromosomes move toward opposite poles
During anaphase I, _____.
homologues separate and migrate toward opposite poles
Chromatids are _____.
identical copies of each other if they are part of the same chromosome
When you cross two heterozygotes (Aa), the F1 generation will be _____.
in the ratio 1:1 homozygotes to heterozygotes
Mendel's principle of independent assortment applies to the __________.
independent assortment of alleles of one gene relative to the alleles of any other gene
During _____, the cell carries out its normal functions and the chromosomes are thinly spread out throughout the nucleus.
interphase
A fragment of chromosome 21 reattaches to chromosome 21, but in the reverse direction. What is the name given to this change?
inversion
A child with cystic fibrosis can be born to two parents who do not have the disease. This is because the disease _____.
is caused by a recessive allele
Our understanding of the role played by genes in many human characteristics is advancing rapidly in, for example, body size, performance on IQ tests, and personality traits. In this new genetic era, the role of the environment __________.
is to work with genes in complex and often unknown ways in the development of these traits
John and Jane are planning a family, but each has a brother who has sickle-cell disease, so they are concerned that their children may develop sickle-cell disease. Neither John, Jane, nor their respective parents have the disease. They consult a genetic counselor who tells them that __________.
it's possible that none of their children will have the disease, but blood tests on them both will be required to make sure
John and Jane are planning a family, but since each has a brother who has sickle-cell disease, they are concerned that their children may develop sickle-cell disease. Neither John, Jane, nor their respective parents have the disease. They consult a genetic counselor who tells them that _____.
it's possible that none of their children will have the disease, but blood tests on them both will be required to make sure
When we say that an organism is haploid, we mean that _____.
its cells each have one set of chromosomes
In some organisms such as certain fungi and algae, cells undergo mitosis repeatedly without subsequently undergoing cytokinesis. What would be the consequence of this?
large cells containing many nuclei
Cystic fibrosis is an inherited disorder that affects which of the following?
lungs
In humans, the _____ determines the sex of the offspring because _____.
male ... the male can contribute either an X or a Y chromosome
If it weren't for _____, chromosome number would double with every generation of sexual reproduction.
meiosis
Variation occurs when chromosomes are shuffled in _____.
meiosis
Looking through a light microscope at a cell undergoing meiosis, you see that the chromosomes have joined into XX-shaped tetrads. These tetrads are lined up along a plane that runs through the center of the cell. This cell is in _____.
meiosis I
At which stage of mitosis are chromosomes lined up in one plane in preparation for their separation to opposite poles of the cell?
metaphase
Which of the following shows mitosis in the correct chronological order?
prophase, prometaphase, metaphase, anaphase, telophase
deletion
The loss of one or more nucleotides from a gene by mutation; the loss of a fragment of a chromosome.
growth factor
A protein secreted by certain body cells that stimulates other cells to divide.
gamete
A sex cell; a haploid egg or sperm. The union of two gametes of opposite sex (fertilization) produces a zygote.
centrosome
A structure found in animal cells from which microtubules originate and that is important during cell division. A centrosome has two centrioles.
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 the offspring trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents? A = big apples; a = small apples; R = red apples; r = yellow apples.
AArr and aaRr
In a certain plant, the alleles A, B, and C are dominant to the alleles a, b, and C. A plant with the genotype AABbcc will have the same phenotype as the plant with the genotype _____.
AaBBcc
benign tumor
An abnormal mass of cells that remains at its original site in the body.
tumor
An abnormal mass of rapidly growing cells that forms within otherwise normal tissue.
malignant tumor
An abnormal tissue mass that can spread into neighboring tissue and to other parts of the body; a cancerous tumor.
nondisjunction
An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.
cell cycle
An ordered sequence of events (including interphase and the mitotic phase) that extends from the time a eukaryotic cell is first formed from a dividing parent cell until its own division into two cells.
somatic cell
Any cell in a multicellular organism except a sperm or egg cell or a cell that develops into a sperm or egg.
chiasma
The microscopically visible site where crossing over has occurred between chromatids of homologous chromosomes during prophase I of meiosis.
Imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the long-finned fish, how can she tell which, if any, of these are homozygous for the trait?
Cross the long-finned fish with short-finned fish; if the offspring are all long-finned, the long-finned parent is homozygous.
In Morgan's testcross of a gray-bodied, long-winged heterozygous female Drosophila with a homozygous recessive black-bodied, vestigial-winged male, the following offspring were obtained: 965 gray body, long wing; 944 black body, vestigial wing; 206 gray body, vestigial wing; 185 black body, long wing. Focusing only on the recombinant classes (gray body, vestigial wing and black body, long wing), the numbers of offspring of each type are similar (206 and 185). What accounts for the similar number of offspring of each recombinant phenotype?
Crossing over between chromosomes is reciprocal, so whenever a recombinant chromosome of one type is produced, there's a recombinant of the opposite type that is also produced.
During meiosis I, homologous chromosomes form a tetrad and crossing over occurs. What is the outcome of crossing over?
Crossing over creates new combinations of genes present on a single chromosome.
Which of the following statements correctly describes the timing of DNA synthesis?
DNA is synthesized in the S phase of interphase.
duplication
Repetition of part of a chromosome resulting from fusion with a fragment from a homologous chromosome; can result from an error in meiosis or from mutagenesis.
Down syndrome
See trisomy 21.
Which of the following is a key difference between meiosis and mitosis?
Synapsis occurs.
Which event occurs only during prophase I of the first meiotic division?
Synapsis of homologous pairs occurs.
The existence of rare XY individuals who are phenotypically normal women was instrumental in learning about human sex determination. Maleness is determined by the SRY gene found on the Y chromosome. How is it possible to be an XY woman?
The SRY locus of the Y chromosome is deleted.
density-dependent inhibition
The ceasing of cell division that occurs when cells touch one another.
What would be the immediate consequence of destroying a cell's centrosomes?
The mitotic spindle would not form.
In corn, blue kernels are produced by a dominant allele of a coloration gene, and white kernels are produced in individuals homozygous for a recessive allele of the same coloration gene. Another gene has two alleles for shape, with smooth kernels being dominant to wrinkled. A plant heterozygous for both genes is testcrossed (crossed to a homozygous recessive white, wrinkled strain). The testcross offspring consist of the following types: 1,447 blue smooth; 1,436 white wrinkled; 150 blue wrinkled; 145 white smooth. Explain the inheritance of the coloration and shape traits.
The coloration and shape genes are linked on the same chromosome.
In corn, blue kernels are produced by a dominant allele of a coloration gene, and white kernels are produced in individuals homozygous for a recessive allele of the same coloration gene. Another gene has two alleles for shape, with smooth kernels being dominant to wrinkled. A plant heterozygous for both genes is testcrossed (crossed to a homozygous recessive white, wrinkled strain). The testcross offspring consist of the following types: 1,447 blue smooth; 1,436 white wrinkled; 150 blue wrinkled; 145 yellow smooth. Explain the inheritance of the coloration and shape traits.
The coloration and shape genes are linked on the same chromosome.
chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes; often used to refer to the diffuse, very extended form taken by chromosomes when a cell is not dividing.
asexual reproduction
The creation of genetically identical offspring by a single parent, without the participation of sperm and egg.
sexual reproduction
The creation of genetically unique offspring by the fusion of two haploid sex cells (gametes), forming a diploid zygote.
zygote
The diploid fertilized egg, which results from the union of a sperm cell nucleus and an egg cell nucleus.
mitosis
The division of a single nucleus into two genetically identical nuclei. Mitosis and cytokinesis make up the mitotic (M) phase of the cell cycle.
cytokinesis
The division of the cytoplasm to form two separate daughter cells. Cytokinesis usually occurs in conjunction with telophase of mitosis. Mitosis and cytokinesis make up the mitotic (M) phase of the cell cycle.
life cycle
The entire sequence of stages in the life of an organism, from the adults of one generation to the adults of the next.
crossing over
The exchange of segments between chromatids of homologous chromosomes during synapsis in prophase I of meiosis; also, the exchange of segments between DNA molecules in prokaryotes.
telophase
The fifth and final stage of mitosis, during which daughter nuclei form at the two poles of a cell. Telophase usually occurs together with cytokinesis.
cleavage furrow
The first sign of cytokinesis during cell division in an animal cell; a shallow groove in the cell surface near the old metaphase plate.
prophase
The first stage of mitosis, during which the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still intact.
anaphase
The fourth stage of mitosis, beginning when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell.
metastasis
The spread of cancer cells beyond their original site.
metaphase
The third stage of mitosis, during which all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle.
Prior to this new technique, how were mice given cancerous tumors?
The tumors were implanted under the skin.
homologous chromosomes
The two chromosomes that make up a matched pair in a diploid cell. Homologous chromosomes are of the same length, centromere position, and staining pattern and possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother.
fertilization
The union of the nucleus of a sperm cell with the nucleus of an egg cell, producing a zygote.
If the diploid number of chromosomes in a certain animal is 6 (2n = 6), there are three sets of two homologous chromosomes each, or three pairs. How do these three pairs align and separate in meiosis?
They align and assort independently to form any of eight different combinations.
Which of the following is true regarding prostate cancer cells?
They can activate and inactivate certain genes.
What defines a short sleeper?
They can function well on 6 hours of sleep or less.
During cell division, what role do centrosomes play?
They organize the microtubules.
Imagine you're counseling a couple who have undergone carrier screening for Tay-Sachs disease. The man is a carrier, and the woman does not carry the Tay-Sachs allele. How should you advise them?
They should be informed that if they have a child, the child will not have Tay-Sachs disease but will have a 50% chance of being a carrier of the Tay-Sachs allele.
Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?
Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.
In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?
Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.
Who wrote that "every cell originates from another existing cell like it."?
Virchow
If the gene for seed color that Mendel studied exhibited pleiotropy, how might a green pea be different from a yellow pea?
With pleiotropy, there would be other differences between the peas - for example, green peas may also be larger, ripen earlier, and be more sensitive to frost.
If the gene for seed color that Mendel studied exhibited pleiotropy, how might a green pea be different from a yellow pea?
With pleiotropy, there would be other differences between the peas—for example, green peas may also be larger, ripen earlier, and be more sensitive to frost.
A woman and her male partner have normal color vision. However, her father and her first son are colorblind. What is her genotype? Use C as the gene for colorblindness.
XCXc
Which of the following indicates Turner syndrome?
XO
Which of the following is a normal human female?
XX
You are an endocrinologist studying new treatments for prostate cancer. You have a patient with an unusually large level of dihydrotestosterone. Which of the following is true?
Your patient's cancer has become resistant to the standard treatment.
Tay-Sachs disease runs in Rebecca's family. On a family pedigree, she saw a shaded circle. This represented _____.
a female with Tay-Sachs
Huntington's disease is an example of a genetic disorder caused by _____.
a late-acting lethal dominant allele
Consider the photograph of a karyotype. This is _____.
a photograph of all a person's chromosomes
If you are a male, the Law of Independent Assortment indicates that your gametes contain _____.
a random mix of the chromosomes you inherited from each parent
Which of the following conditions would prevent cell division due to density-dependent factors?
being completely surrounded by other cells
Which of these factors inhibit(s) cell division?
being completely surrounded by other cells
Asexual and sexual reproduction differ in that sexual reproduction _____.
can produce great variation among the offspring
The risks of sleep deprivation include ____.
cardiovascular disease, memory problems, obesity
A benign and a malignant tumor differ in that _____.
cells of a benign tumor remain within the tumor, whereas cells of a malignant tumor can spread to other body tissues
Looking through a light microscope at a cell undergoing division, you see that the condensed chromosomes have lined up along the midline of the cell. The homologous pairs are NOT joined in tetrads. Each chromosome takes its own place in line, independent of its homolog. You are witnessing _____.
metaphase of mitosis
After fertilization, the resulting zygote begins to divide by _____.
mitosis
During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.
nondisjunction
Down syndrome can be the result of _____.
nondisjunction of chromosome 21 during meiosis
Mendel formulated his principles of inheritance based on _____.
observations on the outcomes of breeding experiments. The underlying processes were unknown at the time.
Duplication of the chromosomes to produce sister chromatids _____.
occurs in both mitosis and meiosis
When applied to Mendel's experiments, the term true-breeding means a self-fertilization of two plants that produces _____.
offspring identical to the parent
The scientist Jean Baptiste Lamarck proposed that if an individual acquired a particular characteristic, such as strength from lifting weights, this characteristic would be inherited by the organism's offspring. This same idea is also part of a more ancient idea, the idea of __________.
pangenesis
Several inherited disorders are much more common in close-knit religious communities, such as the Amish, than in the general population. This is at least partly due to the fact that _____.
people in such communities are more likely to marry relatives
The inheritance of height and weight can best be described as __________.
polygenic and multifactorial
Phenylketonuria (PKU) is an autosomal recessive disorder that can lead to mental retardation and seizures. Using P and p to represent the alleles, what is the genotype of a phenylketonuric person?
pp
Asexual reproduction _____.
produces offspring genetically identical to the parent
The term binary fission is best applied to _____.
prokaryotes
At which point do centrosomes begin to move apart to the opposite poles of the cell in a dividing human liver cell?
prophase
In the telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in _____.
prophase
Crossing over occurs during _____.
prophase I
Synapsis occurs during _____.
prophase I
In Mendel's monohybrid cross of true-breeding purple-flowered and white-flowered peas, all members of the F1 generation were of the _____ phenotype because their genotype was _____ for the flower-color gene.
purple-flowered ... heterozygous
Because it is passed essentially intact from father to son, Y chromosome research has been particularly useful in improving our understanding of __________.
recent human evolution
It is far more common to find human genetic disease caused by _____ alleles than by _____ alleles because _____.
recessive ... dominant ... harmful recessive alleles can survive in the heterozygote without causing any adverse effects on the phenotype
The exchange of parts between nonhomologous chromosomes is called _____.
reciprocal translocation
Benign tumors differ from malignant tumors in that the cells of a benign tumor _____.
remain confined to their original site
The function(s) of meiosis is/are _____.
reproduction (production of gametes)
The cross-fertilization of two different, but true-breeding, varieties of pea plants will _____.
result in hybrid plants
In meiosis II, _____.
sister chromatids are separated