Chapter 13 Meiosis and Sexual Life Cycles Homologous Sister Chromatid Sex Chromosomes Autosomal Chromosomes Autosomes Mitosis Meiosis Haploid Diploid Chromosome Homologous Pair any chromosome that contains genes for a chromosome involved in determining the sex of an organism genetically identical daughter cells Development growth and asexual a single set of chromosomes found in gametes For humans the haploid daughter cells contain a subset of parent cell s genes Preconditions for two complete sets of chromosomes one from each parent For humans the reproduction sexual reproduction formation of gametes Produces 4 haploid cells No homologous pairs only one of each type of chromosome 1 Meiosis I homologous chromosomes are separated 2 Meiosis II sister chromatids are separated number is 23 n 23 diploid number is 46 2n 46 Females XX Males XY characteristics that are not directly related to the sex of an organism chromosomes of the same size and similar structure In their structure homologous chromosomes have the same genes as each other in the same sequence but do not necessarily have the same allele of those genes two identical strands joined by a common centromere Sister chromatids are separated during mitosis so that the two daughter cells would have identical sets of chromosomes Not the same as homologous pairs allele of each gene ova egg cells or sperm fusion of male and female gametes to form a zygote the production of new living organisms by combining genetic information from two individuals of different sexes In most higher organisms a male produces a small motile gamete sperm that travels to fuse with a larger stationary gamete produced by the female egg genes of that parent only Does not involve the fusion of gametes and almost never changes the number of chromosomes genetically identical a very small typically one celled reproductive unit capable of producing a new individual without sexual fusion This is a characteristic of lower plants fungi and other prokaryotic organisms a multicellular haploid generation found in plants and algae that undergo alternation of generations It produces haploid gametes eggs and sperm These egg and sperm cells fuse during sexual reproduction and produce a diploid zygote contains only a single haploid set of chromosomes Each gamete has one the process of fertilizing an egg female animal or plant involving the an organism or cell produced asexually from one ancestor They are a diploid cell resulting from the fusion of two haploid gametes when offspring arise from a single organism and inherit the an organ that produces gametes testis or ovaries Gamete Zygote Fertilization Gonad Sexual Reproduction Clone Spore Asexual Reproduction Gametophyte Sporophyte a multicellular diploid generation found in plants and algae that undergo alternation of generations It produces haploid spores that develop into a gametophyte The gametophyte then makes gametes that fuse and grow into a sporophyte What are the differences between Mitosis and Meiosis Mitosis Meiosis Healing repair helps in multiplication of cells In Somatic cells Asexual sexual organisms Cell divides once Interphase occurs prior to each division DNA replication in interphase DNA replicates once for one division Chromosomes divide once No synapsis Chromatids do not exchange segments during Prophase No Chiasmata No crossing over Centromeres line up at same Metaphase plate Daughter cells identical to parent Centromeres divide in Anaphase Similar chromosomes move towards opposite poles in Anaphase Spindle fibers disappear Nucleoli reappear in Telophase Cytokinesis follows every mitosis produces two cells Chromosome remains constant Formation of gametes maintenance of chromosome in race multiplication of cells not involved In germ cells Sexual organisms Cell divides twice Interphase is only before meiosis I DNA replication in Interphase I DNA replicates once for two divisions Prophase is long few days Chromosomes divide once Synapsis of homologous chromosomes takes place during Prophase Chromatids of homologous chromosomes exchange segments during Prophase Chiasmata occurs Crossing over occurs Centromeres line up in two plates parallel to each other Daughter cells contain maternal paternal genes Centromeres divide in Anaphase II Non similar chromosomes move towards opposite poles in Anaphase I II Spindle fibers don t disappear completely Nucleoli don t reappear in Telophase Cytokinesis occurs after 2nd division produces in four cells Chromosome reduced from the diploid haploid What are the names and stages of Meiosis and what happens in each the chromosomes condense and the nuclear envelope breaks down I Prophase I crossing over occurs II Metaphase I pairs of homologous chromosomes move to the equator of the cell III Anaphase I homologous chrmosomes move to the oppisite poles of the cell IV Telophase I Cytokinesis cytoplasm divides chromosomes gather at the poles of the cells the V Prophase II new spidle forms around the chromosomes VI Metaphase II chromosomes line up at the equator VII Anaphase II cells centromeres divides chromatids move to the opposite poles of the VIII Telophase II Cytokinesis chromosomes the cytoplasm divides nuclear envelope forms around each set of What are the differences between the genetic consequences of sexual and asexual reproduction In asexual reproduction a single individual is the parent and passes copies of all of its genes to its offspring without the fusion of gametes The genomes of the offspring are exact copies of the parent s genome a clone Genetic differences that arise are due to mutations In sexual reproduction two parents give rise to offspring that have a unique combination of genes inherited from the two parents The offspring vary genetically from their sibling and from their parents they resemble family member but are not exact replicas Why does Meiosis produce haploid daughter cells from diploid parents Meiosis produces haploid daughter cells from diploid parents because it consists of two divisions At the start of Meiosis I there is one diploid cell and at the end of the process there are two haploid cells In Meiosis II the cells divide again and result in four haploid cells I II III How do sexual life cycles vary in the timing of Meiosis and fertilization There are three main types of life cycle variations Haploid or diploid cells can divide by Mitosis but only diploid cells can undergo Meiosis since haploid only have one set of chromosomes and cannot
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