assignment_3 (1) BIOL204

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Assignment 3 C (N–Z) For students with first names starting with the letters N to Z. Assignments are graded out of a total of 60 points, and they are worth 9% of your total mark. Submit this assignment after you have completed Unit 3 of the course. Before you submit this assignment, make sure you have read the section on Assignments in your Course Orientation. Part A: Short-answer questions 1. Describe some of the main processes of cancer. (4) Some of the main processes of cancer include: 1. Uncontrolled Cell Growth: Cancer is a condition where cells start growing uncontrollably, dividing and spreading beyond their usual limits. This uncontrolled growth is often caused by changes in the genes that control cell division. 2. Genetic Mutation: genetic changes play an important part in the development of cancer. These changes can be passed down in families or happen over time due to things like exposure to cancer–causing substances, radiation, or mistakes when cells make new DNA copies. 3. Angiogenesis: Cancer cells can encourage the growth of new blood vessels, a process called angiogenesis. This allows tumours to get enough blood supply, providing them with the oxygen and nutrients they need to grow and spread to other parts of the body. 4. Metastasis: Metastasis is when cancer cells break away from the original tumour, travel through the bloodstream or lymphatic system, and establish new tumours in distant organs or tissues. This is a complex process with several steps, including invading surrounding tissues, entering blood or lymph vessels, circulating through the body, escaping the vessels, and taking hold in new locations. 5. Oncogenes: Oncogenes are genes that, when mutated or activated, can drive cancer development by promoting uncontrolled cell growth. They typically encode proteins involved in cell growth and division. Mutations in oncogenes can lead to the production of abnormal proteins Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

that fuel tumour growth. Examples include HER2, EGFR, and MYC. Targeting oncogenes is a key strategy in cancer therapy. 6. Tumour Suppressor Genes: Tumor suppressor genes act as brakes on cancer development by inhibiting cell growth and division. Mutations or inactivation of these genes remove this inhibition, allowing uncontrolled cell proliferation. They regulate cell cycle, DNA repair, and apoptosis. Examples include p53, BRCA1, and PTEN. Therapeutic strategies targeting tumour suppressor pathways are under investigation in cancer treatment. 2. Mitosis almost always results in two identical daughter cells. However, in which cells could one find an exception to that rule? (1) One exception to the rule of mitosis resulting in two identical daughter cells can be found in germ cells (sperm and egg cells). These cells undergo a specialized type of cell division called meiosis, which reduces the chromosome number by half, resulting in daughter cells that are genetically distinct from each other and the parent cell. This genetic diversity is essential for sexual reproduction and the creation of offspring with unique combinations of traits. 3. What is cytokinesis? (1) Cytokinesis is the process of cell division that occurs after mitosis or meiosis. During cytokinesis, the cytoplasm of the parent cell is divided into two daughter cells, each containing a nucleus and other organelles. This division is typically achieved through the constriction of the cell membrane or the formation of a specialized structure called the cleavage furrow in animal cells, or a cell plate in plant cells. Cytokinesis ensures that each daughter cell receives a portion of the cytoplasm and organelles, allowing for the completion of the cell division process. Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

4. Use the following illustration, which shows some stages of three different processes represented by the three columns from left to right, to answer the questions below. (4) 4a. In which columns would you expect genetic recombination? (1) Genetic recombination is the process by which genetic material is exchanged between two homologous chromosomes. It typically occurs during meiosis, specifically during the stages of prophase I. In the given illustration, genetic recombination would be expected in the third stage of column three. 4b. Crossing-over is not shown in this diagram. Which stage in the diagram is closest to the phase where crossing-over occurs? (E.g., “second column, third stage”) (1) Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

Crossing–over , which is the physical exchange of genetic material between homologous chromosomes, occurs during the stage of prophase I in meiosis. In the given diagram, the stage closest to the phase where crossing–over occurs would be the third column, the first stage. 4c. Indicate all stages in the illustration where the nuclear phase (ploidy) has changed. (2) The nuclear phase, or ploidy, refers to the number of sets of chromosomes in a cell. In the given illustration, the stages where the nuclear phase has changed can be identified by looking for changes in the number of chromosomes. Based on the illustration, the stages where the nuclear phase has changed are the first stage in the first column and the second stage in the third column. 5. Compare the final stage of conjugation between an F+ cell and an F- cell with the final stage of conjugation between an Hfr cell and an F- cell. Describe both the donor and the recipient cell and use appropriate terms. (5) In bacterial conjugation, the final stage differs between the conjugation of an F+ cell with an F- cell and that of an Hfr cell with an F- cell. Here’s a comparison: Conjugation between an F+ cell and an F- cell: Donor Cell (F+): The F+ cell contains a plasmid called F (fertility factor) which carries genes for the formation of sex pilus and the transfer of DNA. It can transfer the F plasmid to an F-cell. Recipient Cell (F-): The F- cell lacks the F plasmid and therefore cannot initiate conjugation or transfer genetic material. It acts as the recipient of the F plasmid from the F+ cell. During conjugation between an F+ and an F- cell, the F+ cell extends a sex pilus to the F- cell. The sex pilus facilitates contact between the two cells, allowing the transfer of the F plasmid from the donor (F+) to the recipient (F-). Once the F plasmid is transferred, the recipient cell becomes an F+ cell capable of initiating conjugation with other F- F-cells. Conjugation between an Hfr cell and an F- cell: Donor Cell (Hfr): The Hfr (high frequency of recombination) cell is a bacterial cell in which the F plasmid has integrated into the bacterial chromosome. As a result, it carries chromosomal genes along with the F plasmid genes. Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

Recipient Cell (F-): Similar to before, the F- cell lacks the F plasmid and acts as the recipient of genetic material. In this case, the Hfr cell initiates conjugation by extending a sex pilus to the F-cell. However, instead of transferring only the F plasmid, the Hfr cell transfers a portion of its chromosomal DNA along with the F plasmid. The transfer begins at the point of integration of the F plasmid into the bacterial chromosome and proceeds linearly through the chromosomal DNA into its chromosome through recombination. However, typically, the entire chromosome is not transferred before the conjugation bridge breaks. As a result, the recipient cell remains F-, but it may have acquired new chromosomal genes from the donor Hfr cell. 6. What are the two main differences between recombination in meiosis and recombination through mobile elements? (2) The two main differences between recombination in meiosis and recombination through mobile elements are: 1. Purpose and Occurrence: Meiotic Recombination: Meiotic recombination is a crucial process that takes place during meiosis, the specialized cell division that creates gametes (sperm and egg cells) in sexually reproducing organisms. The main purpose of meiotic recombination is to increase genetic diversity among offspring by shuffling genetic material between matching chromosomes. This natural and essential process is vital for sexual reproduction. Recombination through Mobile Elements: Recombination through mobile elements involves the insertion, deletion, or rearrangement of genetic material mediated by transposable elements (or transposons). Unlike meiotic recombination, which occurs during a specific stage of cell division, recombination through mobile elements can occur at any time during the life cycle of an organism, including both somatic and germ cells. The primary purpose of recombination through mobile elements is not necessarily to increase genetic diversity but rather to promote genetic variation and genome evolution. 2. Mechanism and Scale: Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

Meiotic Recombination: Meiotic recombination involves the physical exchange of DNA segments between homologous chromosomes through the process of crossing over. It typically occurs between alleles located at corresponding positions along homologous chromosomes and results in the formation of recombinant chromosomes in offspring. Recombination through Mobile Elements: Recombination through mobile elements involves the movement of transposable elements within the genome. These elements can insert themselves into new locations within the genome, excise themselves from their original location, or cause rearrangements of adjacent DNA sequences. Recombination through mobile elements can occur at various scales, ranging from small–scale mutations to large–scale genomic rearrangements, depending on the type and activity of the transposable elements involved. 7. Use the following scenario to answer the questions below. (10) Calico cats have orange and black colour patterns that are determined by two genes, O (on the X chromosome) and B (autosomal). A female calico cat mates with a male cat of the genotype OBb . 7a. What is the phenotype of the father? In the given scenario, O represents the allele for orange colouration, while o represents the allele for black colouration. The phenotype of the father cat, determined by the genotype OBb, indicates that the father carries a dominant allele for orange colouration (O) and a heterozygous allele for black colouration (Bb). However, since the allele for black colouration is recessive (o), it doesn't manifest in the phenotype when paired with a dominant allele (O). Therefore, the father cat's phenotype would solely exhibit orange fur due to the presence of the dominant O allele, despite the presence of the heterozygous Bb genotype. 7b. Draw one of the possible Punnett squares for this cross. The Punnett Square should be between a female cat with genotype XOXoBb and a male cat with genotype XoYBb. XOXoBb XoYBb XOXoBb XOOBb XoOBb XOXoBb XOOBb XoOBb Biology 204: Principles of Biology I (Rev. C8) Assignment 3 C

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