biology chapter 8
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
Asexual and sexual reproduction differ in that sexual reproduction _____.
can produce great variation among the offspring
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
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
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
Citokinesis
finishes mitosis by dividing the cytoplasm and organelles of the original parent cell into two separate daughter 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 _____ separate in meiosis I; the _____ separate in meiosis II.
homologous chromosomes ... sister chromatids
During _____, the cell carries out its normal functions and the chromosomes are thinly spread out throughout the nucleus.
interphase
If it weren't for _____, chromosome number would double with every generation of sexual reproduction.
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
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
Duplication of the chromosomes to produce sister chromatids _____.
occurs in both mitosis and meiosis
The function(s) of meiosis is/are _____.
reproduction (production of gametes)
In meiosis II, _____.
sister chromatids are separated
An example of a cell that is 2n is a __________.
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
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
During mitosis, the chromosomes move because _____.
they attach to a dynamic, precisely regulated mitotic spindle
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.
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.
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
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
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.
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
What would be the immediate consequence of destroying a cell's centrosomes?
The mitotic spindle would not form.
Which events occur during prophase?
The nuclear envelope breaks down. && Chromosomes condense and are attached to spindle fibers.
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.
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.