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9 0 / 6 2 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 99/26/09 2:14:23 AM Reproduction of Organisms of Reproduction 2 6

2 6 i . 5 5 4 1 The female sex cell, a(n) egg, forms in an ovary. The female sex a(n) sperm, forms in a testis. The male sex cell, 9 8 _ t u Meiosis forms sex cells with the correct haploid number of chromosomes. This chromosomes. This Meiosis forms sex cells with the correct haploid number of when sex cells maintains the correct diploid number of chromosomes in organisms join. Meiosis creates genetic variation by producing haploid cells. After meiosis I, the two cells formed during this stage go through a second division a second division After meiosis I, the two cells formed during this stage go through II, sister chromatids of the nucleus and cytoplasm called meiosis II. During meiosis separate to produce four haploid cells. Meiosis involves two divisions of the nucleus and the cytoplasm. These divisions, of the nucleus and the cytoplasm. These divisions, Meiosis involves two divisions II, result in four haploid cells. known as meiosis I and meiosis cell grows and duplicates its chromosomes. During interphase, the reproductive separates. During meiosis I, each pair of duplicated homologous chromosomes Sex cells are haploid; they have only one chromosome from each pair of only one chromosome from each pair of Sex cells are haploid; they have chromosomes. and makes four haploid cells. In meiosis, one diploid cell divides Different organisms have different numbers of chromosomes. Different organisms have different pairs of chromosomes that have genes for the same Homologous chromosomes are traits arranged in the same order. Organisms that reproduce sexually make two kinds of cells—body cells and sex cells. kinds of cells—body cells and reproduce sexually make two Organisms that pairs of chromosomes. Body cells are diploid; they have few chromosomes, it will not develop properly. If a zygote has too many or too a. b. The and a sperm cell join together. called fertilization, an egg cell During a process is called a(n) zygote. new cell that forms Sexual reproduction produces an offspring when genetic materials from two from two materials when genetic an offspring produces Sexual reproduction combine. different sex cells O s n A _ F Why is meiosis important? The Phases of Meiosis Haploid Cells Diploid Cells What is sexual reproduction? What is R

C _ 1. 2. 4. 1. 2. 3. 1. 2. 4. 5. 1. 2. 3. 2. 1. 5 T2 E. D. C. B. Lesson 1: Sexual Reproduction Sexual 1: and Meiosis Lesson A. Lesson Outline for Teaching Outline for Lesson 6 0 _ 2 6 0 _ 5 0 2 CC205_062_065_CRF_AnsOut_891455.i62 62 CC205_062_065_CRF_AnsOut_891455.i63 63 2 0 5 _ 0 6 2 _ 0 6 5 _ C R

F Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. _ A n s O u t Reproduction of Organisms ofOrganisms Reproduction diseases, orharshenvironmentalconditions. Searching foramatetakestimeandenergymightexposeindividualstopredators, Organisms havetogrowanddevelopuntiltheyarematureenoughproducesexcells. What aresomedisadvantagesofsexualreproduction? Discussion Question H. G. F. Lesson continued Outline _ 8 2. 1. 3. 2. 1. 2. 1. 9 1 4 Disadvantages ofSexualReproduction Advantages ofSexualReproduction How domitosisandmeiosisdiffer? 5 5 . i 6 3

develop untiltheyarematureenoughtoproducesexcells. One disadvantageofsexualreproductionisthatorganismshavetogrowand Selective breedinghasbeenusedtodevelopdesirabletraitsinplantsandanimals. might beanadvantageiftheenvironmentchanges. Genetic variationgivesindividualswithinapopulationslightdifferencesthat results ingeneticvariationamongindividuals. Sexual reproductionproducesoffspringthathaveanewcombinationofDNA.This cells––two pairsofidenticalhaploidcells. During meiosis,areproductivecellanditsnucleusdividetwiceproducefour produce twoidenticalcells. During mitosisandcelldivision,abodyitsnucleusdivideonce expose individualstopredators,diseases,orharshenvironmentalconditions. Another disadvantageisthatsearching foramatetakestimeandenergymight 6 3 99/26/09 2:14:24AM / T3 2 6 / 0 9

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