Exam 4 Notes

Exam 4 Notes - Exam 4 Notes: DO PROBLEMS AT END OF CHAPTER...

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Exam 4 Notes: DO PROBLEMS AT END OF CHAPTER 14, and 15 Prep Questions: How many chromosomes are required to have one copy of every gene? Or How many chromosomes are required to have one complete copy of all the DNA needed to code for every protein in an organism? Does it matter which species we’re talking about? There could be different amounts. The number of chromosomes in an organism is NOT important. What matters, is how many sets you have, how many copies of the gene you have. Ploidy: the number of sets of chromosomes o Haploid=1 set, 1n o Diploid=2 sets, 2n- most exist as this o Triploid= 3 sets, 3n, really BAD o Tetraploid= 4 sets, 4n o Polyploid- more than 2 sets of chromosomes vs. o Aneuploid- a number of chromosomes in which there is a difference in just one or two extra chromosomes, ex) down’s syndromw Homologous Chromosomes o Chromosomes that carry genes for the same traits (eye color, hair color etc.) are the same length and have their centromere in the same location and same banding pattern. These chromosomes are called homologues, or a homologous pair. o Homologous Chromosomes: Chromosomes containing the same gene Meiosis: produces non identical daughter cells o Non-identical to each other o Not identical to parental cell o They have half the number of chromosomes of the original cell
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o Start with a cell that has 2 chromosomes and end with 4 different cells with single chromosomes o Meiosis results in haploid nuclei being formed from diploid nuclei. o Why only half the number of chromosomes? Sexual reproduction: genetic material from two individuals is brought together. If you don’t cut the cells in half, then the chromosome number keeps doubling. In order to keep the number of chromosomes and amount of DNA constant, you produce gamutes with half the number. o Meiosis is ultimately the setup for sexual reproduction o Does it matter which chromosomes are in each daughter cell? You need to have one copy of every gene, on the other hand, it doesn’t matter which of the two copies goes into a gamute. Stages of Meiosis : As I go through this process pay attention to how the process produces haploid nuclei and divides the chromosomes such that each resulting cell has one chromosome from each pair. Prophase I: homologous chromosomes in synapsis; they are in touch with each other. They actually condense out attached to each other. This is known as Tetrad information Chiasmata: the places where they are joined; Crossing over: because they are joined, they can swap equivalent pieces; essentially this happens every time Metaphase I: the pairs of replicated chromosomes line up on the spindal Anaphase I: the pairs separated from each other. Telophase I:
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This note was uploaded on 06/13/2011 for the course BIOL 1201 taught by Professor Wishtichusen during the Fall '07 term at LSU.

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Exam 4 Notes - Exam 4 Notes: DO PROBLEMS AT END OF CHAPTER...

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