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Unit 5: Reproduction Name: Aim #34 Meiosis: What occurs during the process of meiosis? I. Date: What is Meiosis? What is Meiosis? Which organisms undergo Meiosis? Where does Meiosis occur? 1. The process in which __________________ (______________) are produced. 2. Males produce ______________ cells and females produce ___________ cells through meiosis ____________________ reproducing organisms (humans, animals etc). Egg and sperm cells must be created through meiosis before sexual reproduction can occur. 1. Sperm are produced in the _______________ of males (produced continuously throughout life) 2. Eggs are produced in the ________________ of females (all produced before the female is born) 1. Meiosis begins with _____________________________ with a _____________________ set of What does Meiosis produce? chromosomes (diploid cell = 2 of every chromosome) Ex: In humans, meiosis begins with a body cell with 46 chromosomes (23 pairs) 2. Meiosis ends with ________________________________ with a ______________ set of chromosomes (haploid cell = 1 of every chromosomes) Ex: in humans, meiosis ends with a sperm or egg cell with 23 chromosomes (no pairs) What is Meiosis also known as? II. = the formation of gametes (egg and sperm) through meiosis Chromosomes and Chromosome Number A) Chromosome Number To have a complete set of chromosomes. A cell that has 2 of each chromosome in a pair (1 form each parent) To have a half set of chromosomes. A cell that has 1 of each chromosome not in a pair. Body cells (liver cell, eye cell, heart cell, root cell of a plant etc.) Any cell BESIDES a reproductive cell Gametes (Egg and sperm.) ONLY reproductive cells. 1. The human diploid number is: 2. The human haploid/monoploid number is: 3. One chromosome of each chromosome pair is from the ________________ and one is from the _____________ 4. A human cheek cell has ____________ chromosomes because it is a ________________ cell. 5. A human egg cell has ______________ chromosomes because it is a ________________ cell. 6. The diploid number for an organism is 16. How many chromosomes are in a body cell of that organism? _______. How many chromosomes are in an egg or sperm cell of that organism? ______. So n = _______ & 2n = _______ 7. Complete the chart below # Chromosomes in body cells Horse Fly Spinach Chicken # Chromosomes in gametes # Chromosome pairs in body cells 60 6 12 8 B) Homologous Chromosomes The chromosomes of a body cell (diploid cells) are in the form of ____________________________. Therefore, in a human body cell there are ___________________ of homologous chromosomes o Body cells have 23 chromosomes are from the mother and 23 chromosomes are from the father. o Egg and sperm cells have only one member of this homologous pair Homologous Pairs or Homologous Chromosomes are similar in size/shape, control the same ____________ and have genes for the same characteristic III. Phases of Meiosis: Meiosis involves 2 divisions: Meiosis I and Meiosis II _________ divisions _________ cells created Produces _________ and ____________ Daughter cells are ____________________ to parent cell BEGIN with ONE _______________ CELL END with 4 __________________ CELLS Interphase *MEIOSIS I* (1st Division) Prophase I 1. Chromosomes replicate in one diploid body cell 2. Chromosomes cannot be seen This is the ONLY time during meiosis that the chromosomes replicate 3. Chromosomes from each parent pair up and form homologous pairs 4. Crossing over occurs (homologous chromosomes exchange genetic information, creating new gene combinations) Metaphase I 5. Chromosome pairs line up in the middle of the cell (Pairs have 1 chromosome from mom and 1 from dad) Anaphase I 6. Chromosome pairs are split apart and move to opposite ends of the cell. This is called disjunction Telophase I & Cytokinesis I 7. Cell tears and two daughter cells are created, each with duplicated chromosomes *MEIOSIS II* (2nd Division) Prophase II 8. The two cells each undergo the same process as mitosis except the chromosomes DO NOT replicate again Metaphase II Anaphase II Telophase II & Cytokinesis II 9. Chromatids separate 10. The cytoplasm of each cell tears and 4 haploid sex cells are produced, each with half the number of chromosomes as the original body cell 11. Each cell has 1 chromosome from each pair of homologous chromosomes. Chromosomes are NOT paired Gamete (Sex Cell) Formation IV. How does Meiosis differ in Males and Females? mete (Sex Cell) Formation Meiotic• Division MALES FEMALES In female animals (including = creation of sperm humans), the haploid gametes produced by meiosis are called eggs nimals g humans), id gametes by meiosis Diagram d sperm • The cell divisions at the end of meiosis I & II are uneven, cells are so that 1 large egg is from one produced along with vision 3 other cells, called polar bodies, which are discarded ________ viable _______________ sperm cells What is produced and not involved in reproduction = creation of eggs Cytoplasm divides _________________ Produces ______ large viable egg cell and _____ small nonfunctioning cells called ______________________, which eventually disintegrate Why are gametes produced A haploid sperm and a haploid egg will combine during the process of ____________________ to create a __________________________ (single cell) that will eventually divide by ____________________ and grow into an organism. V. Meiosis as a Source of Genetic Variation The events that occur during meiosis do more than just divide chromosomes into smaller sets and form smaller cells. Meiosis is responsible for much of the genetic variation among sex cells of each individual. A) Independent Assortment: the way the different pairs __________________________ line up in relation to other pairs during metaphase I, leading to many possible combinations in the sex cells that result. B) Crossing Over: When the chromosome pairs (one chromosome from mom + 1 from dad) ________________ parts during prophase I. When they separate, genes are _________________. All 4 cells will now carry ________________ combinations of information. No two sperm cells or egg cells are alike! Origin of new combinations of inheritable traits in offspring & the reason why there’s ______________ within a species VI. Why does this allow a species to evolve? Problems during Meiotic Division Recall that _________________________ occurs during Anaphase I, which is when the chromosome pairs are evenly separate. If this does not properly occur, _________________________ occurs. This results in one sex cell having the Anaphase II Nondisjunction in Meiosis II _____________ amount of chromosomes. An example of a disorder caused by nondisjunction is _______________________. Each body cell will have an extra chromosome the third picture you ee how the lower red hromosome only has ne spindle fiber tached the fourth picture it aused one gamete to ave an extra chromatid nd the other gamete to e missing one. nondisjunction causes e gametes to have the rong amount of hromosomes