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Meiosis • Standard 2a Meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type. • Standard 2b Only sperm and egg (gametes) are made by the process of meiosis. • Standard 2d New combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization) ● Standard 2e Approximately half of an individual’s DNA sequence comes from each parent. - sexual reproduction to produce sperm and eggs -replicating(copying) the DNA/chromosomes once, and dividing twice • Interphase I – DNA replicates • Prophase I – chromosomes pair up **Crossing-Over – chromosomes from the same pair exchange portions producing new combinations (variation) continued Metaphase I –chromosomes line up in the middle Anaphase I –chromosomes separate Telophase I & Cytokinesis – two new HAPLOID cells are formed • Prophase II – chromosomes pair up • Metaphase II – chromosomes line up continued • Anaphase II – sister chromatids separate • Telophase II & Cytokinesis – 4 unique haploid daughter cells are made • In females, 1 becomes an egg In males, all 4 become sperm Fertilization – uniting two haploid cells (egg and sperm) to form a diploid zygote during sexual reproduction -50% of the genetic material comes from each parent. Sex Chromosomes - Male sex chromosomes – XY - Female sex chromosomes – XX Autosomes – all other chromosomes • Production of two genetically identical diploid cells •Production of four genetically different haploid cells, gametes 5 Essential Questions - Meiosis 1. What are chromosomes? 2. Which cells undergo meiosis? Describe the final products of meiosis. 3. What happens to alleles during meiosis? 4. What % of DNA is contributed by a mother? A father? 5. What is the result of fertilization?