B 112 & B122
Introduction: A cell cycle describes the stages of life of a single cell’s life. There is Interphase, Nuclear Division and Cytokinesis. Interphase is the longest which is dividing into three stages: G1, S, and G2. G1 is the stage in Interphase that the new cell grows. In stage S, the cell replicates the DNA. This stage in Interphase is known as synthesis. In G2, the cell produces the proteins needed to undergo Mitosis or Meiosis. Mitosis produces the most cells of the body and produces the exact replica of the nucleus. Mitosis also produces the same amount of chromosomes, as they remain the same in the two daughter cells that would form. Cytokinesis is the final stage in which the original parent cell splits into two daughter cells. Cytokinesis is when the cytoplasm divides in two, producing new cells.(Refer to the picture below for the Cell Cycle) Mitosis has four main stages: Prophase, Metaphase, Anaphase, and Telophase. During prophase the nuclear membrane breaks down as the DNA molecules coil up making chromosomes smaller with centrioles beginning to move to the center poles of the cell. During metaphase the centrioles produce structures called spindles or protein chains. The protein chains attach to the centromeres on the sister chromatids as they line up at the center of the cell. In anaphase, the chains shorten as the sister chromatids are pulled apart from each pair of the cell. Finally in telophase, The nuclear membrane forms around the separated chromosomes. Mitosis can not produce gametes because it keeps the same number of chromosomes in the daughter cell and parent cell. Mitosis is the process in which the body grows and repairs itself. Another type of cell division is Meiosis. Meiosis is a type of cell division that produces gametes, or cells used in sexual reproduction. Every species has a characteristic chromosome. A characteristic chromosome is basically that every specimen in the species has the same amount of chromosomes in their body. Humans have 46 chromosomes with 23 pairs. Meaning that for every human cell, it would contain two copies of each of the 23 different chromosomes that total up to 46. The chromosomes are found in homologous pairs. Gametes are produced by meiosis, another type of cell division. Meiosis produces gametes through two rounds of cell division. Meiosis I is the first stage of meiosis, the homologous chromosomes are separated allowing each daughter cell to have one chromosome from each pair. During the second stage of meiosis, Meiosis II, the chromosomes that were replicated are separated into two chromosomes. The daughter cell still has the same amount of chromosomes, but they are now unreplicated. In the early stages of meiosis, the homologous chromosomes pair up and crossing-over occurs. Crossing over shuffles the genetic material so that each sister chromatid has a different combination of the alleles. An Allele is a version of a gene. There are now four alleles in comparison to two. This is why offsprings have the ability to inherit unique combinations of the alleles. There are four phases during each meiosis round: prophase, metaphase, anaphase, and telophase. In Mitosis, the chromosomes would condense and the nuclear membranes breakdown. Allowing the protein chains from each centriole to connect to the chromosomes. The chromosomes would line up in the center and separate. They are then reeled by the protein chains to the other side of the cell. This produces two daughter cells. However, meiosis is different as the chromosomes that lined up are separated. During Prophase I, the nuclear membrane breaks down as the homologous chromosomes pair up and do crossing-over. In Metaphase I, the protein chains attach to the centromeres of the sister chromatids as they line up at the center of the cell. In Anaphase I, the chains shorten as the homologous chromosomes separate. However in Anaphase I of meiosis, the sister chromatids remain joined. Finally in Telophase I, cytokinesis occurs and two new cells are formed. In Meiosis II, the sister chromatids are separated into different daughter cells. This is very similar to Mitosis. In Prophase II, the chromosomes would condense as protein chains form. In Metaphase II, the chains attach to the centromeres of the sister chromatids as the chromatids line up at the center, similar to Meiosis I. In Anaphase II, the chains are shorten and the chromatids separate. Finally, in Telophase II, the chromosomes begin to elongate as the new nuclear membranes form around the chromosomes. (Refer to the picture below for a graph of each phase) Tips for Testing:
Practice Test: If a human has 46 chromosomes, how many homologous chromosome pair would a human have?
Answer: C is the correct choice because humans will have 23 homologous chromosome pair. If a specimen has 36 homologous pairs of chromosomes, how many chromosomes would be in a gamete?
Answer: B is the correct choice because a gamete has one chromosome for each pair. This means that the gamete would have 36 chromosomes per pair. What is the phase order of Meiosis?
Answer: D is the correct choice because Meiosis I and II both start at Prophase, Metaphase, Anaphase, and finally Telophase. Jerry is analyzing the main differences between Mitosis and Meiosis. What is the main difference between Mitosis and Meiosis? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Answer: Mitosis is slightly different than Meiosis because they are both forms of Cell Division. However, Mitosis is Cell Division primarily used to repair the cells in the body by replicating itself. This means that the genetic material will be identical with the same number of chromosomes. In Meiosis, this form of cell division is mostly used in reproduction. Meiosis allows unique sister chromatids to form through crossing over. The sister chromatids will remain joined as two new cells are formed after Meiosis I. Describe all of the phases in Meiosis II. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Answer: Similar to Meiosis I, Meiosis II has Prophase, Metaphase, Anaphase, and Telophase. In Prophase II, the protein chains will form again as the chromosomes condense. In Metaphase II, the protein chains will attach itself to the centromeres at the center of the cell. During Anaphase II, the protein chains shorten as the sister chromatids are separated. Finally, in Telophase II, the new cell will elongate and nucleic membranes will form around the new four daughter cells. B121 & B122 A cell must first duplicate its nucleus in order for it to form two genetically identical daughter cells. If the parent cell has 46 chromosomes, the daughter cell would also have 46 chromosomes. DNA replication produces the same exact copy of the genetic material in a chromosome. A chromosome consists of two arms and a centromere in the center. DNA replication creates an identical copy that is still connected to the centromere, this is known as a sister chromatids. They will remain connected until Nuclear division. DNA replication is carried out by enzymes, as an enzyme, DNA helicase, binds to the site of a double stranded DNA and begins to separate it. DNA polymerase moves along the strands pairing with the nucleotides in the strand. DNA replication is known as a semiconservative replication. This means that the double strands consist of one original strand and a newly assembled one. Each Homologous chromosome is very similar, and have nearly the same DNA sequences. However, they have different alleles. Allele is a version of a gene. Gametes are drastically different. Each sperm/egg cell only contains half the number of chromosomes. Each gamete holds a chromosome from each pair, only one allele for a gene. The offspring inherits a chromosome from each homologous pair from each parent. The alleles in an organism determines the organism’s traits. Traits are usually polygenic. A polygenic trait is determined through many different genes. There are dominant and recessive alleles. A phenotype is the appearance of the trait. Whereas genotype is the combination of alleles of a specific gene. Dominant alleles are usually represented by the capital letters and the recessive alleles are represented by the lowercase letters. A dominant allele is expressed if an individual inherits a single copy of the allele. A recessive allele is expressed if the individual inherits two copies of the allele. Tips for Testing:
Practice Test: What does DNA replication do?
Answer: A is correct because DNA replication produces the exact same copy of the genetic material in the chromosome. What is also known as a semiconservative replication?
Answer: C is the correct choice because a semiconservative replication is known as DNA replication. In what phase does the cell replicate in? What is the stage of the phase?
Answer: B is correct because the cell replicates DNA (synthesis) in Interphase S stage. How is Genetic Information inherited from the parent cell? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Answer: Genetic Information is inherited from the parent cell because crossing over allows the chromatids to have a unique allele combination. The genetic information is also inherited when the sister chromatids separate. Genetic Information is inherited from one chromosome of each pair from your mother and father. The Genes contains the inheritance from your parents. Why is Meiosis importance to inheritance for offsprings? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Answer: Meiosis allows the chromatids in the cell to cross-over and split into daughter cells. The chromatids will separate again as they split into new cells. Meiosis is important for offsprings because it allows it to gain a unique combination of alleles and increase genetic variations.
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