...MECHANISM OF MEIOTIC CROSSING OVER: The mechanism of crossing over includes the following stages i.e., Synapsis, Duplication of chromosomes, Crossing over and Terminalization. i. Synapses: It is the intimate pairing between two homologous chromosomes (one maternal and another paternal) during zygotene stage of prophase I of meiosis. Synapsis often starts when the homologous ends of the two chromosomes come together on the nuclear envelope and it continue inward in a zipper-like manner from both ends aligning the two homologous chromosomes side by side. By synapsis each gene is thus brought into juxtaposition i.e. side by side. The resulting pairs of the homologous chromosomes are called bivalents. ii. Duplication of chromosomes: The synapses are followed by the duplication of chromosomes (in pacytene stage). During this stage, each homologous chromosome of bivalents split longitudinally and form two identical sister chromatids which remain together by the centromere. This stage of four chromatids in the pair is called tetrad. iii. Crossing over by breakage and union: Crossing over occurs in the homologous chromosomes only during the four stranded or tetrad stage. Homologous chromosome continue to stay in synapis for days during pacytene stage and chromosomal crossing over occurs due to exchange of chromosomal material between non-sister chromatids of each tetrad. During crossing over, two non-sister chromatids first break at the corresponding points due to activity of...
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...Cell Cycle Questions for Cell Cycle 1) . Briefly describe all phases of the cell cycle and tell what happens in each. a) Interphase: G1 phase, S phase, G2 phase Interphase: Before a cell can enter cell division, it needs to take in nutrients. All of the preparations are done during the interphase. Interphase proceeds in three stages, G1 phase, S phase, G2 phase. Cell division operates in a cycle. Therefore, interphase is preceded by previous cycle mitosis and cytokinesis (Module 3 Readings). a. G1 phase: The cell increases the supply of proteins and increases its organelles. b. S phase: Linear chromosome is replicated. c. G2 phase: Increases protein preparing to replicate. (Module 3 Readings) b) M phase: M phase is a method of indirect cell division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. 2) Which phase is the shortest? Anaphase is the shortest phase of mitosis because its where the chromatids twins are all pulled apart at the centromere by the spindle fibers. 3) What is G0 (Gap 0/Resting phase)? A resting phase is when or where the cell has left the cycle and has stopped dividing. 4) If a cell never entered the resting phase would it be a problem? Why? It would continually reproduce, bypassing all the reproduction checkpoints, which would greatly increase the chance of it becoming cancerous or making defects and mutations...
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...hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation The roles of mitosis Chromosome • A DNA molecule & attached proteins • Duplicated in preparation for mitosis 1 2/24/2013 Chromosomal Organization A chromosomes is DNA associated with proteins. The entire complex is tightly wound and compressed into a discrete, linear structure. The Cell Cycle • • • • • Interphase Usually longest part of the cycle Cell increases in mass Number of cytoplasmic components doubles G1, S, and G2 phases Chromosomes duplicate in S phase of interphase Chromosome Duplication a One chromosome (unduplicated) Duplication allows a whole copy of the genome to reside in each daughter cell one chromatid one chromatid b One chromosome (duplicated) two sister chromatids Each duplicated chromosome will split. One sister chromatid will be in each new daughter cell 2 2/24/2013 Chromosome Number • Sum total of chromosomes in a cell • Somatic (body) cells – Chromosome number is diploid (2n) – Two of each type of chromosome Human Chromosome Number • Diploid chromosome number (n) = 46 • Two sets of 23 chromosomes each • Gametes (Sex cells) – Chromosome number is haploid (n) – One of each chromosome type • Mitosis produces cells with 46 chromosomes-two of each type • X and Y chromosomes...
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...one hundred trillion cells. You made hundreds of different types of tissues and dozens of organs including a brain that makes you do remarkable things. Where there is sex there is verity, when it comes to the survival of fittest verity has the definite advantage. All though sexual reproduction is popular it is tricky if you look into a man’s testical it is packed with coiled up tubing if stretched out would expand over half a mile. Inside that tubing an average man is turning out 1000 new sperm every second. That is about 100 million new sperm ever day. And each sperm is one of a kind carrying a unique genetic package. This is all possible through a process called meiosis. In almost every cell in your body you have 30,000 or more different genes spread out on very long strands of DNA called chromosomes. Each of us is made up of trillions of cells. Inside each cell is a nucleus that contains rod like structures called chromosomes, which store and transmit genetic information. Most cells have two versions of each different type of chromosomes total of 46 chromosomes. Twenty three came from your mother and twenty three from your father. They come in pairs where they are quite similar but not exactly the same. The only time they get together is during meiosis. The documentary discusses in...
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...haploid cells. A haploid cell is a cell that has a single copy of each chromosome and a diploid has two copies. Meiosis consists of Meiosis I and Meiosis II which both consist of the four phases Prophase, Metaphase, Anaphase, and Telophase. When entering the stages of Meiosis chromosomes first go into the phase of Prophase I with 46 chromosomes. In Prophase I condensing, synapsis (when two of homologous chromosomes line up together), and the crossing over of chromosomes occur. Synapsis creates tetrads which consist four chromatids. Crossing over is the recombination of genetic information between two homologous chromosomes. In between Prophase and Metaphase is...
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...the diploid body cells of an animal that are not involved in a gamete formation. gametic cell- a cell that fuses with another cell during fertilization in organisms that reproduce sexually, homologous chromosome , sister chromatid, karyotype, autosome and sex chromosome. How many chromosomes are in a human somatic cell? 46 How many homologous chromosome pairs are in a human somatic cell? 22 How many chromosomes are in a human gamete? 23 How many homologous chromosome pairs are in a human gamete (trick question)? 46 Which stage of the human life cycle is diploid (2n)? Which is haploid (n)? Which processes form the transition from haploid to diploid and diploid to haploid? Meiosis- The goal of meiosis is to produce four haploid gametes from one diploid somatic cell. This occurs through two cell divisions: meiosis I and meiosis II. Interphase - as in mitosis, the DNA content of the cell doubles from 2n to 4n. Meiosis I- Prophase I. DNA supercoils, tetrads form and crossing over occurs between maternal and paternal homologous chromosomes. Metaphase I. Homologous chromosome pairs line up along the equator of the cell in stacks instead of end to end. The random alignment of the homologous chromosomes during metaphase I is known as independent assortment. Anaphase I. Homologous chromosome pairs separate toward opposite poles of the cell. Nondisjunction can occur at this stage. Telophase I/cytokinesis. Nuclei reform in each of the two daughter cells as the mother cell is split in half by...
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...variation? Introduction Most cells in organisms that reproduce sexually are diploid. They have two sets of chromosomes and two complete sets of genes. Gametes are an exception. Gametes are the cells that combine during sexual reproduction. In animals, these cells are called sperm and eggs. Gametes are haploid cells with only one set of chromosomes. Meiosis is the process in which haploid cells form from diploid cells. In this lab, you will model the steps in meiosis. You will make drawings of your models. You will also identify points in the process that can lead to greater genetic variation. Skills Focus Use Models, Sequence, Draw Conclusions Materials • pop beads • magnetic centromeres • large sheet of paper • colored pencils • scissors Safety Do not direct the points of the scissors toward yourself or others. Use the scissors only as instructed. Pre-Lab Questions 1. Control Variables Why must you use the same number of beads when you construct the second chromosome in Step 1? Name Class Date 2. Infer Why is the longer chromosome pair used to model crossing-over? 3. Calculate A diploid cell has two pairs of homologous chromosomes. How many different combinations of chromosomes could there be in the gametes? Procedure The diploid cell in your model will have two pairs of homologous chromosomes. In order to keep track of the pairs, you will make one pair longer than the other. The beads will represent...
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...Chromosomes are thread like gene carrying structures found in the nucleus. Each chromosome consists of one DNA molecule and associated proteins (ghr.nlm.nih.gov). Genes are segments of DNA. These are the units which make up chromosomes, responsible for the inheritance of specific characteristics. Alleles are alternate versions of genes. A dominant allele is the version of that gene that is always shown as the characteristic. A recessive allele is only shown if there is no dominant allele present inherited information is passed on in the form of each genes specific sequence of nucleotides that make up DNA. Most genes programme cells to synthesise proteins that produces an organisms inherited traits. Traits are organisms’ characteristics. The transmission of hereditary traits is based on the replication of DNA which produces copies of genes that can be passed on from parents to offspring. Humans have 46 chromosomes in almost all cells (apart from sex cells for example sperm and egg cells which are haploid or have half the number of chromosomes) Sexual reproduction results in greater degree of variation. Two parents give rise to offspring that have unique combinations of genes inherited from two parents. Sexual reproduction generates genetic variation by homologous parings (half of the chromosomes form the mother and half from the father). The process crossing over is the exchange of genetic material which enhances variation in a species; it produces recombinant chromosomes...
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...surrounding structures and are cancerous Malignant tumors can break away and start new cancers elsewhere through the process of metastasis What Is Cancer? Cancer cells differ from normal cells: Divide when they should not Invade surrounding tissue Move to other locations in the body What Is Cancer? All tissues that undergo cell division, such as ovarian tissue, are susceptible to cancer Cancer Risk Factors Known risk factors are linked to particular cancers… Not all exposures to chemicals and radiation causes cancers Cell Division Overview Cell division produces new cells in order to: Heal wounds Replace damaged cells For growth Also for reproduction Cell Division Overview DNA is organized into structures called chromosomes which can carry hundreds of genes along their length The number of in each cell depends on the organism: humans have 46 Cell Division Overview The “rungs” of the molecule are the bases: A (adenine) T (thymine) G (guanine) C (cytosine) Cell Division Overview The bases across the “ladder” are connected in a specific way: A always bonds with T C always bonds with G The connection is a hydrogen bond Cell Division Overview James Watson and Francis Crick: Determined the...
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... Using the pictures & phases above, describe what is happening in each phase: a. Interphase: G1 – cell grows; S-DNA is duplicated; G2 – cells grows & makes sure all the organelles are duplicated. b. Prophase I: nuclear membrane breaks down; nucleolus disappears; centrioles begin to migrate to opposite sides of the cell; spindle fibers begin to form; homologous chromosomes form; crossing over occurs c. Metaphase I: homologous chromosomes are lined up down the middle of the cell d. Anaphase I: homologous chromosomes are pulled apart & sister chromatids are pulled to opposite sides of the cell, cell has gone from diploid to haploid e. Telophase I: nuclear membrane reforms, nucleolus reappears; spindle fibers disappear; cell divides in 2 f. Prophase II: nuclear membrane breaks down; nucleolus disappears; centrioles begin to migrate to opposite sides of both cells; spindle fibers begin to form; sister chromatids form g. Metaphase II: sister chromatids are lined up down the middle of both cells. h. Anaphase II: sister chromatids are pulled apart & chromosomes are pulled to opposite...
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...In prophase I of meiosis I, there are 5 sub-stages. The first one is leptotene where the chromosome starts to condense. Followed by zygotene was the pairing of the homologous chromosome and become closely associated during synapsis and the formation of the Synaptonemal complex. The third sub-stage is pachytene were the crossing over occur, forming chiasmata, which hold homologous chromosome together. In diplotene, the Synaptonemal complex start to disappear and in the last stage, diakinesis, the Synaptonemal complex is completely disappearing. In metaphase I, the pair of homologous chromosome aligns along the metaphase plate in double row. The formation of chiasmata before are to help keep the pairs together and position the pairs such that only one side of each homologue’s centromere faces outward toward of the cell’s poles. Thus kinetochore microtubules attach to only one side of each centromere; a kinetochore microtubules from one pole of the cell attaches to one homologue of the chromosome while a kinetochore microtubules from the other cell poles attaches to other homologue. In anaphase I, kinetochore microtubules shorten and homologous pairs are pulling apart. One duplicated homologue goes to the other poles. Sister chromatids do not separate. This is in contrast to mitosis, where duplicated homologues line up individually on the metaphase plate, kinetochore microtubules from opposite poles of the cell attach to opposite sides of one homologue’s centromere, and sister...
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...increase genetic variation than is asexual reproduction. E) Only asexual reproduction results from the union of a sperm and an egg. Answer: D 3) Strictly speaking, the phrase "like begets like" refers to A) all forms of reproduction. B) sexual reproduction only. C) asexual reproduction only. D) production of gametes from a premeiotic cell. E) sexual reproduction between different species. Answer: C 4) Asexual reproduction requires ________ individual (s). A) 0 B) 1 C) 2 D) 3 E) 4 Answer B 5) With the exception of identical twins, siblings who have the same two biological parents are likely to look similar, but not identical, to each other because we have A) identical chromosomes, but different genes. B) identical genes but different chromosomes. C) the same combination of traits, but different genes. D) only a 20% chance of sharing the same combination of genes. E) a similar but not identical combination of genes. Answer: E 6) Virchow's principle, stated formally in 1858, was that A) animals must always reproduce. B) photosynthesis is the center of all life. C) animals must develop. D) every cell comes from a cell. E) all life evolves. Answer: D...
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...cells and its importance in maintaining chromosome numbers during asexual reproduction. Cell Cycle and Mitosis A. The cell cycle is the growth and division of cells. There are three main parts of the cell cycle: Interphase,mitosis, and cytokinesis. 1. In Interphase the cell begins to grow...
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...one is the Y chromosome? A: I would tell them it is the chromosome that is not labeled. Q: 2. Look at each gamete. How many "Chromosome 1's" (the one with the Horns gene) are in each of these cells? A: 1 Q: 3. Do you think all the offspring of these parents will look like this one? Why or why not? A: All the offspring of the parents would make the baby dragon look like its mother, as you can see. the baby dragon has no traits from the father whatsoever, other than two legs, but the baby dragon is identical to the mother....
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...Unit 5: Meiosis & Mendel Test Review Packet Chapter 13: What is the difference between diploid and haploid? How are they represented? Which type of reproduction will result in genetically identical offspring? What is the difference between a somatic and germ cell? What is a karyotype? Explain what is meant by homologous chromosomes. Sketch a diagram that correctly represents: sister chromatids, homologous chromosomes, centromere and then answer the following questions about your diagram. How many chromosomes does your cell have? How many homologous pairs of chromosomes? How many chromatids? Is the cell haploid or diploid? What is the process that produces gametes? What is another term for a fertilized egg? How does the chromosome number of a...
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