Lecture 11 Inheritance and Sexual Life Cycles Bio Exam 2 Asexual reproduction results in genetically identical offspring o The offspring is a clone of the parent the cell just divides Asexual reproduction is genetically the same as cloning Sexual reproduction results in genetically similar but not identical offspring o With sexual reproduction there is a combination of genes Asexual reproduction is the result of mitosis Chromosomes exist as homologous pairs in diploids Know and understand why meiosis produces haploid daughter cells from diploid parents o Meiosis produces haploid daughter cells from diploid parents because meiosis creates sex cells Two haploid daughter cells one from each parent will combine and create a diploid offspring Know that sexual life cycles alternate meiosis and fertilization o Sexual life cycles between meiosis and fertilization because meiosis produces haploid cells These cells only have half the chromosomes needed to become offspring so when the cells become fertilized with another haploid cell they become diploid Know that sexual life cycles vary in the timing of meiosis and fertilization o Vocab Haploid A cell containing only one set of chromosomes Diploid A cell containing two sets of chromosomes 2n one set inherited from each parent Homologous chromosome homologous pair A pair of chromosomes of the same length centromere position and staining pattern that possess genes for the same characters at corresponding loci One homologous chromosome is inherited from the organism s father the other from the mother Also called homologs or a homologous pair Sister chromatid Two copies of a duplicated chromosome attached to each other by proteins at the centromere and sometimes along the arms While joined two sister chromatids make up one chromosome Chromatids are eventually separated during mitosis or meiosis II Gamete A haploid reproductive cell such as an egg or sperm Gametes unite during sexual reproduction to produce a diploid zygote Zygote The diploid cell produced by the union of haploid gametes during fertilization a fertilized egg Meiosis A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication It results in cells with half the number of chromosome sets as the original cell Fertilization 1 The union of haploid gametes to produce a diploid zygote 2 The addition of mineral nutrients to the soil Gonad The male and female sex organs the gamete producing organs in most animals Sexual reproduction A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from both parents via the gametes Asexual reproduction The generation of offspring from a single parent that occurs without the fusion of gametes by budding division of a single cell or division of the entire organism into two or more parts In most cases the offspring are genetically identical to the parent Clone 1 A lineage of genetically identical individuals or cells 2 In popular usage an individual that is genetically identical to another individual 3 As a verb to make one or more genetic replicas of an individual or cell See also gene cloning Spore 1 In the life cycle of a plant or alga undergoing alternation of generations a haploid cell produced in the sporophyte by meiosis A spore can divide by mitosis to develop into a multicellular haploid individual the gametophyte without fusing with another cell 2 In fungi a haploid cell produced either sexually or asexually that produces a mycelium after germination Gametophyte In organisms plants and some algae that have alternation of generations the multicellular haploid form that produces haploid gametes by mitosis The haploid gametes unite and develop into sporophytes Sporophyte In organisms plants and some algae that have alternation of generations the multicellular diploid forms that result from the union of gametes The sporophyte produces haploid spores by meiosis that develops into gametophytes Lecture Information VERY IMPORTANT diploidy vs haploidy has NOTHING to do with sister chromatids Homologous chromosomes genetically similar but not necessarily identical Sister chromatids of same chromosome genetically identical Know the difference between homologs and sister chromatids Meiosis produces haploid daughter cells by separating homologous pairs of chromosomes so Lecture 12 that one homolog goes to each cell Meiosis consists of two stages o Meiosis I the first division of 2 stage process of cell division in sexually reproducing organisms that result in cells with half the number if chromosome sets as the original o Meiosis II the second division of 2 stage process of cell division in sexually reproducing organisms that result in cell with half the number of chromosome sets as the original cell end product of meiosis II is 4 haploid cells homologous chromosomes are separated in meiosis I sister chromatids are separated in meiosis II Stages of Meiosis I o Prophase I cross over and synapsis occur homologs come together and become homologous pair Due to cross over sister chromatids are not identical o Metaphase homologous chromosome pairs line up at the metaphase plate o Anaphase homologous chromosome pairs pulled apart o Telophase I 2 haploid cells form because 2 different nucleus but no chromosome duplication Stages of Meiosis II o Prophase spindles start to form o Metaphase Chromosomes line up at metaphase plate Become attached to microtubles o Anaphase Sister chromatids separate o Telophase Cytokinesis cells split again 4 haploid cells because 2 split into to 2 more Daughter cells are genetically distinct from each other and parent pairing of homologs and crossing over both occur in prophase I Understand that both the random assortment of homologs into daughter cells and The processes of crossing over result in genetically variable gametes infinite amount of crossing over posssibilities that make everyone genetically different Differences between mitosis and meiosis o Mitosis o Meiosis DNA replication occurs during interphase before mitosis begins Number of Divisions one including prophase prometaphase metaphase anaphase and telophase Synapsis of Homologous Pairs does not happen of Daughter cells and genetic composition 2 each diploid 2n and genetically identical to the parent cell Role in Animal Body enables multicellular adult to arise from zygote produces cells for growth repair and in some species
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