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
When we say that an organism is haploid, we mean that _____.
its cells each have one set of chromosomes
An example of a cell that is 2n is a __________.
After fertilization, the resulting zygote begins to divide by __________.
The diploid phase of the human life cycle begins with _____.
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
Which of the following statements regarding sexual and asexual reproduction is true?
Sexual reproduction is more likely to increase genetic variation than is asexual reproduction.
Meiosis starts with a single diploid cell and produces
our haploid cells.
A cell preparing to undergo meiosis duplicates its chromosomes during
During prophase I of meiosis,
homologous chromosomes stick together in pairs.
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?
Meiosis I produces _____ cells, each of which is _____.
two ... haploid
Meiosis II typically produces _____ cells, each of which is _____.
four ... haploid
During _____ sister chromatids separate.
At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
Synapsis occurs during _____.
Homologous chromosomes migrate to opposite poles during _____.
During _____ chromosomes align single file along the equator of a haploid cell.
At the end of _____ and cytokinesis there are four haploid cells.
During _____ a spindle forms in a haploid cell.
Chromatids are _____.
identical copies of each other if they are part of the same chromosome
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.
DNA replication occurs in _____.
the S phase of interphase
The function of meiosis is to make __________.
four cells with a haploid number of chromosomes
In a cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing _____ chromosomes.
Crossing over is _____.
the exchange of homologous portions of nonsister chromatids
During which stage of meiosis do synapsis and crossing over occur?
At the end of telophase I of meiosis, as cytokinesis occurs, there are __________.
two haploid cells
At the conclusion of meiosis I, the daughter cells are _____.
haploid and the sister chromatids are joined
In meiosis II, _____.
sister chromatids are separated
What is the typical result when a diploid cell undergoes meiosis?
four haploid cells
Mitosis and cytokinesis result in the formation of __________; meiosis and cytokinesis result in the formation of __________.
two diploid cells : four haploid cells
Meiosis differs from mitosis in that _____ only occurs in meiosis.
Which of the following statements regarding the differences between mitosis and meiosis is false?
Crossing over is a phenomenon that creates genetic diversity during mitosis.
The exchange of parts between nonhomologous chromosomes is called _____.
Crossing over is important because it _____.
allows the exchange of genes between homologous chromosomes
With the exception of identical twins, siblings who have the same two biological parents are likely to look similar, but not identical, to each other because they have
a similar but not identical combination of genes.
During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.
How many pairs of autosomes do humans have?
Down syndrome can be the result of _____.
nondisjunction of chromosome 21 during meiosis
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.
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.
Which of the following indicates Turner syndrome?
Polyploidy is involved in which of the following examples?
A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes.
Which of the following types of organisms commonly demonstrates polyploidy?
How many generations does it take to develop a new plant species by polyploidy?
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 _____.