Bio Test 3

Meiosis I vs. Meiosis II

- Meiosis involves two cell divisions. In meiosis I, homologous chromosomes pair up and are then separated into the two daughter cells. Therefore, although the parent cell is diploid (has two of each chromosome), the two daughter cells produced by meiosis I are haploid (have only one of each chromosome). The chromosomes present in the cells generated by meiosis I are still replicated (pairs of sister chromatids). - In meiosis II, the sister chromatids are separated. The four daughter cells that result are haploid with unreplicated DNA.

Select ALL statements that correctly describe mitosis and meiosis.

- Mitosis and meiosis both begin with cells that have replicated chromosomes. - Two diploid cells are produced when a dipoid cell divides by mitosis; division of a diploid cell by meiosis produces four haploid cells. - In mitosis, the daughter cells are genetically identical, but in meiosis the daughter cells are genetically different.

Which of the following statements, if any, correctly describes a difference between prokaryotic and eukaryotic cells/organisms? - Prokaryotic cells only divide by mitosis; eukaryotic cells only divide by meiosis. - Sister chromatids are found in prokaryotic cells; homologous chromosomes are found in eukaryotic cells. - All prokaryotic cells are haploid; all eukaryotic cells are diploid. - Prokaryotes only reproduce asexually; eukaryotes only reproduce via sexual reproduction. - None of the above

- None of the above ***All prokaryotic cells are haploid because they only have one chromosome. Eukaryotic cells, however, can be either haploid (e.g. gametes) or diploid (e.g. your body cells). Therefore, the terms homologous chromosomes and sister chromatids ONLY apply to eukaryotic cells, and ONLY diploid eukaryotic cells have homologous chromosomes. Prokaryotic cells (e.g. bacteria) divide by binary fission, and NOT my mitosis (or meiosis!). Haploid eukaryotic cells can divide by mitosis; diploid eukaryotic cells can divide by mitosis or meiosis. Division of a prokaryotic cell IS asexual reproduction - all prokaryotic organisms are unicellular (one cell), and the daughter cells produced are genetically identical (and identical to the parent cell). Some eukaryotes reproduce sexually, while others (e.g. single-celled eukaryotes like yeast; some multi-cellular eukaryotes) reproduce asexually.

In a human lung cell, a substitution mutation occurs in a gene on one chromosome, but not in the homologous chromosome. What will be found in the daughter cells when this cell divides by mitosis?

both daughter cells will have one mutated and one non-mutated copy of the gene

Expression of the human gene human gene CNCR produces a protein that's important for controlling cell division. A mutation in the CNCR gene that has been linked to various types of cancer increases the activity of the CNCR protein. Based on this information, which of the following is a reasonable prediction?

- The protein produced by expression of the CNCR gene promotes cell division. **Cell division is tightly controlled. There are certain proteins that prevent a cell from dividing before it's ready (e.g. the DNA has not been replicated yet), or if there are issues that could be problematic if the cell divides (e.g. significant DNA damage). Other proteins promote cell division when a cell is ready to divide. Mutations that increase the activity or expression of proteins that promote cell division can cause cells to divide uncontrollably, leading to cancer.Mutations inhibit the function/expression of proteins that prevent cell division can also result in uncontrolled growth and cancer. Remember that cancer-promoting mutations must occur in MULTIPLE cell division regulatory genes for a cell to become cancerous.

Select ALL statements that correctly describe BOTH prokaryotic division (binary fission) and mitosis. - The two copies of a chromosome generated by DNA replication are distributed to opposite ends of a dividing cell. - Nuclear envelope (membrane) breaks down. - DNA is replicated once prior to division. - Produces two genetically identical daughter cells. - Parent cell can be diploid.

- The two copies of a chromosome generated by DNA replication are distributed to opposite ends of a dividing cell. - DNA is replicated once prior to division. - Produces two genetically identical daughter cells. **** All of a cell's DNA must be copied once (and only once) prior to any type of cell division. In both binary fission and mitosis, the two copies of a chromosome (the one chromosome in a prokaryotic cell; each of the multiple chromosomes in a eukaryotic cell) must be distributed to opposite sides of a dividing cell so that each daughter cell produced has a complete set of genetic information. Both binary fission and mitosis result in two daughter cells that are genetically identical. Prokaryotic cells CANNOT be diploid; they only have one chromosome (one piece of DNA). Prokaryotic cells lack organelles, so they do NOT have nuclei.

A diploid cell has 16 total chromosomes (pieces of DNA). Therefore, the cell has _____ pairs of homologous chromosomes prior to DNA replication, and after the cell has replicated its DNA, there will be _____ pairs of homologous chromosomes.

- eight; eight ***Diploid cells have two sets of chromosome - one set inherited from the egg and the other set inherited from the sperm that fertilized the egg. Therefore, a diploid cell with 16 total chromosomes has eight homologous pairs (eight pairs of chromosomes with the same genes). Although the total amount of DNA in a cell doubles when DNA replication occurs, the number of homologous pairs does NOT change. Each chromosome is now a pair of sister chromatids (the two identical copies of a chromosome that stick together following replication).

The daughter cells produced by meiosis I are _________. The daughter cells produced by meiosis II are ________.

- haploid; haploid ***Homologous chromosomes are separated in meoisis I, therefore the daughter cells are haploid with replicated chromosomes. Meiosis II separates sister chromatids generating haploid daughter cells with unreplicated chromosomes.

In some organisms (e.g. certain fungi and algae), all steps of mitosis occur normally except cells do not undergo the last step, cytokinesis. The daughter cells produced when this happens

- have more than one nucleus and more total chromosomes than the parent cell. ** Cytokinesis is the last step of mitosis (and is sometimes classified as a separate event that follows mitosis). In cytokinesis, fibers form a ring and pinch a dividing cell in half to form two daughter cells. Cytokinesis occurs after sister chromatids have been distributed to opposite sides of a cell and new nuclear membranes have formed around the chromosomes at each end. Therefore, cells that undergo the other steps of mitosis normally, but not cytokinesis, will have more than one nucleus. Remember that all DNA is replicated prior to mitosis, so if a cell is not split into two cells, there's going to be twice as much DNA in the cell. Each of the two nuclei will contain the same number of chromosomes present in the nucleus of the parent cell, so there will be double the number of total chromosomes compared to the parent cell.

When do homologous chromosomes pair up?

- meiosis I only *** In meiosis I, homologous chromosomes form pairs. This is important because it allows each chromosome of a homologous pair to be distributed to a different daughter cell, resulting in haploid cells (one of each chromosome). Homologous chromosomes do NOT pair up in mitosis and CANNOT pair up during meiosis II because the homologous chromosomes have already been separated in meiosis I.

An error occurs during division of a cell that results in a daughter cell with both sister chromatids of a replicated chromosome. This error could have occurred during

- mitosis or meiosis II. ** Sister chromatids are separated in BOTH mitosis and meiosis II, therefore this error could have occurred during either of these processes.

How many alleles for the FUZY gene could there be in a population of caterpillars?

- more than two different alleles **A diploid organism has two alleles for every gene that can be the same or different. For example, an individual caterpillar could have two brown bristle alleles, or they could have a brown bristle allele and a black bristle allele. In a species, it is possible for more than two different alleles for a particular gene exist. For example, in a caterpillar population, one caterpillar could have a brown bristle and a black bristle allele, and another caterpillar could have a black bristle allele and an orange bristle allele. The presence of more than two different alleles for a particular gene within a species is common.

A diploid cell has six pairs of homologous chromosomes. How many individual chromosomes (pieces of DNA) will be copied during DNA replication?

- twelve **In DNA replication, ALL DNA in a cell is replicated. If a cell has six pairs of homologous chromosomes, it has twelve total pieces of DNA (two each of the six different chromosomes).

Meiosis I vs. Meiosis II

Meiosis I: - produces two daughter cells DNA replicated prior to process - homologous chromosomes are separated - daughter cells have replicated chromosomes Meiosis II: - daughter cells have unreplicated chromosomes - produces four daughter cells - sister chromatids are separated

Which of the following, if any, correctly compares homologous chromosomes and sister chromatids?

Homologous chromosomes can have the same or different alleles for each gene; sister chromatids always have the same alleles for each gene. **** Homologous chromosomes are pairs of chromosomes with the same genes, and therefore are only present in diploid cells. One of the homologous chromosomes in a pair was inherited from the egg and the other one from the sperm during fertilization. Although homologous chromosomes ALWAYS have the same genes, they CAN have different alleles (versions of a gene) for one or more of the genes. Sister chromatids are the two copies of a chromosome generated by DNA replication. Therefore, sister chromatids ALWAYS have the same genes AND alleles. Unless errors occurred during DNA replication, the sequences of sister chromatids are identical.

FUZY is a gene involved in determining bristle ("fur") color in a certain species of caterpillar, which is a diploid organism. Therefore, an individual caterpillar

has two alleles for the FUZY gene.