Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Meiosis and Sexual Life Cycles Asexual Reproduction Sexual Reproduction One parent, mitotic division 2 parents, meiotic division identical offspring, clones Unique offspring Somatic cell vs. Gametes Homologous chromosomes • 23 Pairs, one from each parents • Carry the same genes Sex chromosomes Autosomes • Carry different genes • Determine sex (X and Y) • Everything besides the X and Y chromosome Diploid vs. Haploid Cells Fertilization – fusion of nuclei of 2 gametes • Forms a zygote • How many chromosomes does a zygote have? Human life cycle: meiosis only in gametes • Variations found in other organisms •Meiosis I: homologous chromosomes separate, 2 diploid cells produced •Meiosis II: sister chromatids separate, 4 haploid cells produced •Interphase only occurs before Meiosis I Prophase I • Chromosomes condense, homologs pair by gene, crossing over • Centrosomes move, spindle fibers form, envelope breaks • Kinetochores attach Telophase I and Cytokinesis Metaphase I • Pairs of homologous chromosomes line up at equator • Both chromatids are attached to same microtubule • Each half has haploid set of chromosomes • Cytokinesis occurs, forms 2 new cells Anaphase I • Homologs separate to opposite sides • Sister chromatids still connected Prophase II Spindle apparatus forms Sister chromatids move toward center Metaphase II Chromosomes move to equator Sister chromatids not identical! Anaphase II Sister chromatids separate Move to opposite poles Telophase II & Cytokinesis Nuclei form, chromosomes uncoil, cytokinesis occurs 4 haploid cells produced If a haploid cell has 24 chromosomes, how many does the diploid have? The gene for eye color would be found on which type of chromosome? If a genetic disorder is found on the Xchromosome, why might males be more prone to it? Compare and Contrast Mitosis and Meiosis. MITOSIS 1 division (PPMAT) MEIOSIS • Prophase, prometaphase, metaphase, anaphase, telophase Occurs in somatic cells 2 Diploid cells Daughter cells genetically identical to parent Used for growth, repair, asexual reproduction 8 stages (2 divisions) • Meiosis I & II Occurs in gametes 4 Haploid cells Daughter cells genetically unique Used to reduce # of chromosomes in cell Independent assortment (2n possibilities) Crossing Over • Homologous genes pair • Maternal & Paternal genes exchanged • Chiasma forms Random Fertilization Best variations survive Pass on genes Genes eventually dominant in a population = natural selection