bio exam 3

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

Normal human gametes carry _____ chromosomes

23. This is the number of chromosomes in a single set of human chromosomes.

Part complete A certain species of animal has six pairs of chromosomes. How many DNA molecules are present in the nuclei of these animals during G2 phase?

24 DNA replication is completed during S phase, which occurs prior to G2 phase. Since each chromosome (12) is replicated, there are 24 DNA molecules in the nucleus during G2 phase

In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes.

2^23 (2 to 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.

On average, what percentage of infants born to 45-year-old mothers have Down syndrome?

3% To calculate the risk of an infant being born with Down syndrome, divide the number of Down syndrome births on the graph by 1,000. Then, to convert that number to a percentage, multiply by 100%

Part complete A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

16 16 is half of 32.

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.

92 Mitosis follows the S phase, during which the cell's DNA is duplicated.

Which of the following checkpoints does occur late in G1?

A check that the cell is large enough for division A check that nutrients are sufficient A check that growth factors are present

Part complete Polyploidy is involved in which of the following examples?

A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes Seedless watermelons have acquired an entire extra set of chromosomes, which makes them polyploid.

Part complete What is the difference between a benign tumor and a malignant tumor?

Benign tumors do not metastasize; malignant tumors do.

A cell replicates its entire chromosomal DNA only __

before it is about to divide This ensures that genetic material can be appropriately distributed to each of the daughter cells

Part complete A cleavage furrow forms in an animal cell during ___

cytokinesis In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two

Part complete 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.

Meiosis II typically produces _____ cells, each of which is __

four ... haploid

Variation occurs when chromosomes are shuffled in _____.

meiosis Variation is produced as a result of independent assortment and crossing over.

Part complete 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.

The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?

Prophase Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the nuclear envelope breaks up.

Part complete The exchange of parts between nonhomologous chromosomes is called _____.

Reciprocal translocation Which is the exchange of genetic material between nonhomologous chromosomes

Part complete The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?

Telophase Which is the final phase of mitosis, when the chromosomes have arrived at the poles and the nuclear envelopes of the two new cells form.

What must happen before a cell can begin mitosis?

The chromosomes must be duplicated, which occurs during interphase.

Use the graph and your knowledge of Down syndrome to select the three true statements.

The incidence of Down syndrome in infants born to mothers under the age of 35 is less than 0.5%. Down syndrome is caused by a trisomy of chromosome 21. The risk of having a baby with Down syndrome more than doubles for 45-year old mothers compared to 40-year old mothers

Consider the photograph of a karyotype. This is ____

a photograph of all a person's chromosomes Karyotypes, ordered displays of a person's chromosomes, are useful in identifying chromosomal abnormalities.

Crossing over is important because it _________

allows the exchange of different versions of genes between homologous chromosomes Crossing over, by combining DNA from two parents into a single chromosome, is an important source of genetic variation in sexual life cycles

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 _____

an inversion

Part complete During _____ sister chromatids separate.

anaphase II Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid

Gametes are produced by _____

meiosis

Part complete During _____ chromosomes align single file along the equator of a haploid cell

metaphase II Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

Part complete During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.

nondisjunction In nondisjunction, chromosomes fail to separate properly at meiosis

Part complete Down syndrome can be the result of _____

nondisjunction of chromosome 21 during meiosis Down syndrome is the result of an extra chromosome 21.

asexual reproduction

process of reproduction involving a single parent that results in offspring that are genetically identical to the parent

Synapsis occurs during _____.

prophase I

During _____ a spindle forms in a haploid cell.

prophase II Prophase II is essentially the same as mitotic prophase except that the cells are haploid.

Part complete At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each

At the end of _____ and cytokinesis there are four haploid cells.

telophase II

What is different concerning the DNA in bacterial cells as opposed to eukaryotic cells?

the amount of DNA present whether the DNA is housed in a nucleus or not whether the DNA is linear or circular

Synapsis

the pairing of homologous chromosomes

Part complete 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. In this case, the cells would stimulate their own growth and grow far more extensively than normal cells dependent on the limiting amounts of growth factor present in the medium.

Which of the following checkpoints does not occur late in G1?

Chromosome replication does not occur until after G1; this checkpoint is a G2 checkpoint.

At the end of the mitotic (M) phase, the cytoplasm divides in a process called __________

Cytokinesis Which is the division of the cytoplasm that occurs in conjunction with telophase, the last phase in mitosis.

The first step of bacterial replication is _____

DNA replication

True or false. Mitosis takes place during M phase of the cell cycle, which is longer than interphase.

False Mitosis does indeed take place during M phase, but M phase is shorter than interphase; cells spend most of their time in interphase.

The chromosomes line up in the center of the cell during which phase of mitosis?

Metaphase which occurs in the middle of mitosis, when the chromosomes line up in the middle of the cell

Part complete The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?

Anaphase

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 Except for the occurrence of rare mutations, this is always the case. Both sister chromatids come from replication of a single DNA molecule, which is present in the one chromatid before replication.

Bacteria divide by:

binary fission

Asexual and sexual reproduction differ in that sexual reproduction ____

can produce great variation among the offspring As long as there is some genetic variation in the parents, different offspring will inherit unique combinations of genes from each parent, creating variation among offspring.

The function of meiosis is to make __________

four cells with a haploid number of chromosomes The two cell divisions of meiosis, I and II, produce four haploid daughter cells, which are not genetically identical to the diploid parent cell.

Part complete Meiosis I produces _____ cells, each of which is __

two ... haploid