sperm egg zygote 2 different embryos Dizygotic twins having unique DNA two eggs

Sperm egg zygote 2 different embryos dizygotic twins

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sperm→ egg→ zygote→ 2 different embryos Dizygotic= twins having unique DNA; two eggs released at once; fraternal twins - Sperm #1→ egg #1→ zygote #1→ embryo #1 - Sperm #2→ egg #2→ zygote #2→ embryo #2 9.6 Mitosis= adds and replaces identical cells; growth, development, etc. Parent cell→ 2 identical diploid daughter cells; all cells are diploid, besides gametes Meiosis= produces haploid gametes with unique DNA; 2 rounds of cell division to create 4 genetically unique haploid cells - Genetic diversity increased in Prophase I (crossing over) and Metaphase I (independent assortment; homologous chromosomes line up in Metaphase I; in Metaphase II, sister chromatids line up) 9.7
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Most chromosomal disorders are caused by errors during Meiosis: nondisjunction= chromosomes not separated properly in Meiosis I and Meiosis II Aneuploidy= extra or missing chromosomes - Trisomy 21: down syndrome; extra copy of chromosome 21 - Trisomy 18: edward syndrome ; three copies of chromosome 18 Nondisjunction of sex chromosome-- chromosome 23-- causes sex disorders - *** table 9.2*** - Can be lethal Polyploidy= extra complete set of chromosomes - Fertilize to double amount of chromosomes; occurs in some plants; haploid→ diploid→ triploid→ tetraploid
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  • Spring '16
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