Genetics and Crossing Over

Table of Content
genetically identical offspring
During asexual reproduction, yeast cells can produce _____.
The term binary fission is best applied to _____.
distribution of a copy of the single parental chromosome to each daughter cell
In bacterial cells, binary fission involves _____.
A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes.
There are _____ chromatids.
they have uncoiled to form long, thin strands
Individual chromosomes are usually observed with a light microscope during
mitosis, even though cells spend more time in interphase. This is because
identical copies of each other if they are part of the same chromosome
Chromatids are _____.
100 units
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?
the S phase of interphase
DNA replication occurs in _____.
during the S phase
Chromatids form _____.
In the telophase of mitosis, the mitotic spindle breaks down and the
chromatin uncoils. This is essentially the opposite of what happens in _____.
At which point do centrosomes begin to move apart to the opposite poles of
the cell in a dividing human liver cell?
The phase of mitosis during which the chromosomes move toward separate
poles of the cell is _____.
They organize the microtubules.
During cell division, what role do centrosomes play?
the beginning of the formation of the mitotic spindle
One event occurring during prophase is _____.
anaphase and telophase
Single sister chromatids are found in cells at mitotic _____.
metaphase—chromosomes line up on the equatorial plane.
Which of the following is a correct representation of an event that occurs in
Chromatids separate
Which of the following occurs during mitosis?
At which stage of mitosis are chromosomes lined up in one plane in
preparation for their separation to opposite poles of the cell?
sites at which microtubules attach to chromosomes
The kinetochores are _____.
large cells containing many nuclei
In some organisms such as certain fungi and algae, cells undergo mitosis repeatedly without subsequently undergoing cytokinesis. What would be the
consequence of this?
division of the cell outside the nuclear material
Cytokinesis refers to _____.
formation of a cleavage furrow
Cytochalasin B is a chemical that disrupts microfilament formation. This
chemical would interfere with _____.
A cleavage furrow forms in an animal cell during _____.
being completely surrounded by other cells
Which of the following conditions would result in inhibition of cell division due
to density-dependent factors?
Benign tumors do not metastasize; malignant tumors do.
What is the difference between a benign tumor and a malignant tumor?
do not exhibit density-dependent inhibition
Observations of cancer cells in culture support the hypothesis that cancer cells
are genetically identical to the parent cell (assuming no mutation has occurred)
The function of mitosis is to produce daughter cells that _____.
How many pairs of autosomes do humans have?
Which of the following is a normal human female?
male . . . the male can contribute either an X or a Y chromosome
In humans, the _____ determines the sex of the offspring because _____.
somatic cell
An example of a cell that is 2n is a _____.
After fertilization, the resulting zygote begins to divide by _____.
its cells each have one set of chromosomes
When we say that an organism is haploid, we mean that _____.
The diploid phase of the human life cycle begins with _____.
telophase I and prophase II
At a critical point in meiosis, the chromosomes do not replicate. This occurs between _____.
homologous chromosomes move toward opposite poles
In anaphase I, _____.
four haploid cells
What is the typical result when a diploid cell undergoes meiosis?
In a cell containing 10 chromosomes, meiosis results in the formation of
daughter cells containing _____ chromosomes.
two haploid cells
At the end of telophase I of meiosis, as cytokinesis occurs, there are _____.
prophase I
Synapsis occurs during _____.
sister chromatids separate and migrate toward opposite poles
During anaphase II, _____.
homologues separate and migrate toward opposite poles
During anaphase I, _____.
prophase I
Crossing over occurs during _____.
An organism has a haploid chromosome number n = 4. How many tetrads will
form during meiosis?
Synapsis of homologous pairs occurs.
Which event occurs only during prophase I of the first meiotic division?
four cells with a haploid number of chromosomes
The function of meiosis is to make _____.
Synapsis occurs (during meiosis, not mitosis)
Which of the following is a key difference between meiosis and mitosis?
two diploid cells . . . four haploid cells
Mitosis and cytokinesis result in the formation of _____; meiosis and
cytokinesis result in the formation of _____.
Variation occurs when chromosomes are shuffled in _____.
In humans, the haploid number of chromosomes is 23. Independent
assortment has the possibility of producing _____ different gametes.
They align and assort independently to form any of eight different combinations
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?
prophase I
Crossing over occurs during _____.
allows the exchange of genes between homologous chromosomes
Crossing over is important because it _____.
an inversion
Unless the chromosomes were stained to show band patterns, a karyotype
would usually be unable to show _____.
Extra copies of the other somatic chromosomes are probably fatal
Why are individuals with an extra chromosome 21, which causes Down
syndrome, more numerous than individuals with an extra chromosome 3 or
chromosome 16?
Each cell in an individual with Down syndrome contains _____ chromosomes.
During meiosis, homologous chromosomes sometimes “stick together” and do not separate properly. This phenomenon is known as _____.
nondisjunction of chromosome 21 during meiosis
Down syndrome can be the result of _____.
Which of the following indicates Turner syndrome?
A normal watermelon has 22 chromosomes but seedless
watermelons have 33 chromosomes.
Polyploidy is involved in which of the following examples?
an inversion
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 _____.
reciprocal translocation
The exchange of parts between nonhomologous chromosomes is called

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