Flashcards in Chapter 13 Questions Deck (89)
A human cell containing 22 autosomes and a Y chromosome is
Which life cycle stage is found in plants but not animals?
Homologous chromosomes move toward opposite poles of a dividing cell during
Meiosis II is similar to mitosis in that
the daughter cells are diploid
If the DNA content of a diploid cell in the G1 phase of the cell cycle is x, then the DNA content of the same cell at metaphase of meiosis I would be
If we continued to follow the cell lineage from question 5, then the DNA content of a single cell at metaphase of meiosis II would be
How many different combinations of maternal and paternal chromosomes can be packaged in gametes made by an organism with a diploid number of 8 (2n = 8)?
Asexual reproduction _____.
produces offspring genetically identical to the parent
-Only one individual makes a genetic contribution to the offspring.
What number and types of chromosomes are found in a human somatic cell?
44 autosomes and 2 sex chromosomes
-Human somatic cells contain 22 pairs of autosomes and either two X chromosomes (in females) or an X and a Y chromosome (in males).
For what purpose(s) might a karyotype be prepared?
-for prenatal screening, to determine if a fetus has the correct number of chromosomes
-to determine whether a fetus is male or female
-to detect the possible presence of chromosomal abnormalities such as deletions, inversions, or translocations
-Karyotypes can show if all of the chromosomes are present, and whether an individual is male (XY) or female (XX). In addition, by staining the chromosomes and examining the resulting banding patterns, it is possible to detect defects such as deletions, translocations, and inversions.
In alternation of generations, what is the diploid stage of a plant that follows fertilization called?
-The sporophyte is the diploid, multicellular stage of the plant that produces haploid spores by meiosis.
How are sister chromatids and homologous chromosomes different from each other?
Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication.
-One homologous chromosome comes from the father, and the other comes from the mother. Sister chromatids are identical copies of each other.
Mitosis results in the formation of how many cells; meiosis results in the formation of how many cells?
two diploid cells ... four haploid cells
-In mitosis a cell that has doubled its genetic material divides to produce two diploid daughter cells. In meiosis a cell that has doubled its genetic material undergoes two rounds of division, producing four haploid cells.
Which of the following occurs during meiosis but not during mitosis?
-The pairing of homologous chromosomes that only occurs during prophase I of meiosis is called synapsis.
What is crossing over?
the exchange of homologous portions of nonsister chromatids
-The result is new combinations of genetic material (genetic recombination).
Genetic variation occurs when chromosomes are shuffled in fertilization and what other process?.
-Variation is produced as a result of independent assortment and crossing over.
Heritable variation is required for which of the following?
-Variation is the raw material of evolution.
Human gametes are produced by _____.
-Meiosis produces haploid gametes from a diploid parental cell.
Normal human gametes carry _____ chromosomes.
-This is the number of chromosomes in a single set of human chromosomes.
Once meiosis I is completed,
cells are haploid.
A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.
-16 is half of 32.
Meiosis I produces _____ cells, each of which is _____.
two ... haploid
-At the end of meiosis I there are two haploid cells.
Meiosis II typically produces _____ cells, each of which is _____.
four ... haploid
-At the end of meiosis II there are typically 4 haploid cells.
The events of prophase II are essentially the same as those of
mitotic prophase except that prophase II cells are haploid.
During anaphase II sister chromatids
separate and migrate to opposite poles.
Four haploid cells are present at the end of
telophase II and cytokinesis.
During _____ sister chromatids separate.
-Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.
At the end of telophase I and cytokinesis there are
two haploid cells
At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
-At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.
Homologous chromosomes pair during
Metaphase II is essentially the same as
mitotic metaphase except that the cells are haploid.
During metaphase I
tetrads align along the metaphase plate.
Synapsis occurs during _____.
-Synapsis, the pairing of homologous chromosomes, occurs during prophase I.
Homologous chromosomes migrate to opposite poles during _____.
-During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.
During _____ chromosomes align single file along the equator of a haploid cell.
-Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.
During anaphase I
homologous chromosomes, consisting of sister chromatids, migrate to opposite poles.
At the end of _____ and cytokinesis there are four haploid cells.
-At the end of telophase II and cytokinesis there are four haploid cells.
During _____ a spindle forms in a haploid cell.
-Prophase II is essentially the same as mitotic prophase except that the cells are haploid.
During interphase the centrosome
duplicates and the chromosomes are not condensed.
How many genes are present in the human genome?
tens of thousands
What is a locus?
the precise location of a gene on a chromosome
-The location of a gene within the genome, including the identity of the particular chromosome that it maps to and its specific position on that chromosome, is called its locus.
Sexual and asexual reproduction are alike in that _____.
they can both occur in multicellular organisms
A clone is the product of _____.
Unless the chromosomes were stained to show band patterns, a karyotype would be least likely to show which of the following?
part of a chromosome turned around
-An inversion, which affects neither the number of chromosomes nor the length of a chromosome, is generally difficult to detect without staining to show chromosomal bands.
A karyotype is _____.
a photograph of all of an individual's chromosomes
-Karyotypes, ordered displays of an individual's chromosomes, are useful in identifying chromosomal abnormalities.
Fertilization produces _____.
a diploid zygote
-Fertilization always involves the fusion of gametes and produces a diploid zygote.
Which, if any, of the following statements is true?
-Diploid cells can divide by mitosis.
-Diploid cells can divide by meiosis.
-Haploid cells can divide by mitosis.
-Haploid cells cannot divide by meiosis.
Which of the following is part of the life cycle called alternation of generations?
-multicellular haploid stage (gametophyte)
-multicellular diploid stage (sporophyte)
--In alternation of generations, zygotes give rise to multicellular, diploid sporophytes, and spores give rise to multicellular, haploid gametophytes.
The sexual cycle of the multicellular algal genus Fucus involves _____.
mitosis, meiosis, and fertilization
-All multicellular organisms undergo mitosis, and all diploid, sexually reproducing organisms undergo meiosis and fertilization, which are complementary processes.
A life cycle in which the only multicellular form is haploid is most typical of _____.
-In most fungi, the multicellular form is haploid, and fertilization (and creation of a zygote) is immediately followed by meiosis.
In sexually reproducing species, the chromosome number remains stable over time because _____ and _____ always alternate.
meiosis ... fertilization
The egg (ovum) of a rabbit contains 22 chromosomes. How many chromosomes are in the somatic (body) cells of a rabbit?
-Haploid sex cells contain half as many chromosomes as diploid somatic cells.
In a diploid cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing _____ chromosomes.
-Haploid sex cells contain half as many chromosomes as diploid somatic cells.
How many pairs of autosomes do humans have?
-humans have 23 pairs of chromosomes.
Sister chromatids _____.
are identical copies of each other formed during DNA synthesis
Which of the following statements about homologous chromosomes is correct?
They have genes for the same traits at the same loci.
-The chromosomes that make up a pair are called homologous chromosomes, and they carry genes controlling the same inherited characters.
Humans have 46 chromosomes. This number of chromosomes will be found in _____.
When we say that an organism is haploid, we mean that _____.
its cells have a single set of chromosomes
Which of the following is a function of mitosis in humans?
multiplication of body cells
-Mitosis distributes a copy of all of the chromosomes to the two new daughter cells, keeping the chromosome number constant.
Somatic cells in humans contain _____ set(s) of chromosomes and are therefore termed _____.
two ... diploid
-Somatic cells in interphase contain the characteristic diploid chromosome number.
Nearly all life cycles have both haploid and diploid phases. Usually, the transition from haploid to diploid takes place _____.
at fertilization, when gametes fuse
-The union of haploid gametes at fertilization produces the zygote, or fertilized egg, which marks the beginning of the diploid phase of the life cycle.
Spores and gametes are different in that _____.
gametes can fuse to form a zygote, but spores can develop into independent organisms without first forming a zygote
-Unlike a gamete, a spore gives rise to a multicellular organism without fusing with another cell.
Which of the following results in cells that contain half the parental chromosome number?
-Mitosis results in the production of daughter nuclei that contain the same number of chromosomes as the parental nucleus.
At the end of telophase I of meiosis and the first cytokinesis, there are _____.
two haploid cells
What is the result when a diploid cell undergoes meiosis?
four haploid cells
-The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.
Synapsis occurs during _____.
-Synapsis is the pairing of homologous chromosomes during prophase I.
Which of the following occurs during anaphase II?
Sister chromatids separate and migrate toward opposite poles.
Which of the following occurs during anaphase I?
Homologs separate and migrate toward opposite poles.
Cytokinesis is the _____.
division of one cell into two
-Cytokinesis normally accompanies both telophase I and telophase II, as well as the telophase of mitosis.
What is the function of meiosis?
to make cells with a haploid (half that of the parents) number of chromosomes
What is the function of mitosis?
to make exact copies of the parent cell
Crossing over occurs during _____.
-Crossing over resulting in genetic recombination occurs during this phase.
Regions of chromosomes where nonsister chromatids cross over are called _____.
the structures at centromeres where the spindle fibers attach to the chromosome.
The synaptonemal complex _____.
physically connects homologous chromosomes during prophase I
-The synaptonemal complex is broken down late in prophase I.
An organism has a haploid chromosome number n = 4. How many tetrads will form during meiosis?
-Each tetrad consists of two chromosomes.
Which event occurs only during prophase I of the first meiotic division?
Synapsis of homologous pairs occurs.
-Synapsis of homologous chromosomes occurs at prophase of meiosis I.
In a male mammal, every cell that undergoes meiosis gives rise to _____ sperm.
-The cell cycle produces two daughter cells from one parental cell.
Which of the following occurs in meiosis, but not mitosis?
Homologous chromosomes separate.
-Homologous chromosomes separate during anaphase I. This event follows synapsis, an event unique to prophase I.
Which function makes meiosis lengthier and more complex than mitosis?
-decreasing the chromosome number to haploid
-introducing genetic variation among the daughter cells
-ensuring that each daughter cell gets a single, complete set of chromosomes
-undergoing two rounds of cytokinesis
--Meiosis involves two divisions that typically result in four daughter cells (instead of two). Each cell has half the number of chromosomes of the original parent cell, and is, of course, not genetically identical to the parent cell.
Ignoring crossover, how many kinds of gametes can be produced by an organism with a diploid number of 8?
-The number of combinations possible when chromosomes assort independently into gametes during meiosis is 2^n, where n is the haploid number of chromosomes.
Which of the following contributes to genetic variation in sexually reproducing species?
random fertilization, independent assortment, crossing over
-These three aspects of sexual reproduction increase genetic variation.
In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing _____ different types of gametes.
-For each gamete there are two possibilities for each chromosome (the paternal or the maternal chromosome), and there are 23 different chromosomes per gamete.
The diploid number of chromosomes in a certain animal is 8 (2n = 8). How do the four pairs of homologous chromosomes align and separate during meiosis?
They align and assort independently to form any of 16 different combinations.
-Because each pair of homologous chromosomes is positioned independently in metaphase I, the first meiotic division results in the independent assortment of paternal and maternal chromosomes into daughter cells. In a case in which 2n = 8, 16 combinations of chromosomes are possible for gametes.
In a diploid set of chromosomes, one member of each pair of homologous chromosomes is derived from the father (paternal), and the other comes from the mother (maternal). If 2n = 6, what is the probability of obtaining a gamete in which all the chromosomes are paternal ones?
-The chance of any one paternal chromosome ending up in a particular gamete is 1/2, so the chance that all three would be of paternal origin would be (1/2)n, where n = 3.
The major contribution of sex to evolution is that _____.
it provides a method to increase genetic variation
Which of the following answers is not involved nor an outcome of crossing over?
the random alignment of homologous pairs of chromosome at metaphase I
-Crossing over involves the breakage and exchange of DNA between homologous pairs.
Which of the following statements reflects an advantage that sexual reproduction likely provides over asexual reproduction?
Although energetically more costly than asexual reproduction, sexual reproduction leads to different combinations of alleles that could provide adaptability in a changing environment.
-Although sexual reproduction can greatly increase the genetic variation in a population, its energetic costs are higher than for asexual reproduction.