BIOL HW8
In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes. View Available Hint(s)
2 by the power of 23 - For each gamete, there are two possibilities for each chromosome (the paternal or the maternal chromosome), and there are 23 different chromosomes per gamete. Crossing over can increase this number even further.
Meiosis starts with a single diploid cell and produces
4 haploid cells
Polyploidy is involved in which of the following examples?
A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes
Chromatids are _____.
identical copies of each other if they are part of the same chromosome
A cell preparing to undergo meiosis duplicates its chromosomes during
interphase.
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?
prophase I. - Segments of nonsister chromatids trade places during prophase I, resulting in recombination.
A diploid organism whose somatic (non-sex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.
16 is half of 32.
Normal human gametes carry _____ chromosomes.
23. This is the number of chromosomes in a single set of human chromosomes.
how many moms at 40 have risk of down syndrome babies
3%
What is the difference between a benign tumor and a malignant tumor?
Benign tumors do not metastasize; malignant tumors do
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.
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 - After reactivation, these cells move into G1. Here they grow in preparation for DNA replication (S phase). Once complete, the cells move into G2 and make the final preparations for mitosis.
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. - The separation of the duplicating chromosomes ensures that each daughter cell receives a 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 within any given cell, regardless of the total number of X chromosomes
In the telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in _____.
Prophase - During prophase we observe the formation of the spindle, the condensation of chromatin, and the disappearance of the nucleolus
What are haploid cells?
Sister chromatid cells joined together
During anaphase II, ____
Sister chromatids separate and migrate toward opposite poles.
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.
Consider the photograph of a karyotype. This is __
a photograph of all a person's chromosomes
Meiosis differs from mitosis in that _____ only occurs in m
crossing over - Crossing over, the exchange of corresponding segments between nonsister chromatids of homologous chromosomes, only occurs during meiosis.
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 - Cytokinesis in plant cells would be blocked because the cell plate that ultimately separates one cell into two is formed from coalescing vesicles.
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 cell plate, which divides the cytoplasm in two, forms during telophase of mitosis in a plant cell and can be observed in the center of this image.
During anaphase I, __________.
homologous chromosomes separate and migrate toward opposite poles
During prophase I of meiosis,
homologous chromosomes stick together in pairs
When we say that an organism is haploid, we mean that _____.
its cells each have one set of chromosomes - A cell with a single chromosome set is called a haploid cell. Organisms with this type of cells are haploid organisms.
variation occurs when chromosomes are shuffled in _____.
meiosis - Variation is produced as a result of independent assortment and crossing over.
Gametes are produced by _____.
meiosis/ Meiosis produces haploid gametes from a diploid parental 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?
n 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.
The correct order of events during meiosis is
prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II.