Lecture 12.0 and 12.3

• Meiosis is the production of sex cells (gametes)
• Gametes must contain half the chromosomes.
• A gene is a section of DNA that influences a trait
• Different versions of a specific gene are

  called alleles
• Organisms with three or more versions of each

  type of chromosome are called polyploid
• Meiosis 1- Organisms with three or more versions of each

  type of chromosome are called polyploid
• Meiosis 2- Organisms with three or more versions of each

  type of chromosome are called polyploid
• In early prophase one: Chromosomes Condense

  • Spindle apparatus begins to form

  • Nuclear envelope begins to breaks down
• Structure that results from synapsis is called a bivalent.
• Homologus chromosomes pair together in a process called synapsis.
• • In late prophase I

  • Nuclear envelope finishes breaking down

  • The two homologs attach to microtubules from opposite poles of

  the spindle apparatus
• homologs are joined a points called chiasmata
• In late prophase one, chromosomes cross over.
• Crossing-over produces new combinations of alleles within a

  chromosome
• In metaphase 1 homologous pairs line up at the metaphase plate.
• independent assortment is when each homologous pair is random of each other pair.
• In anaphase 1 the homologous pairs sepparate to each side of the cell.
• In telophase 1 the homologs finish migrating to the polls of the cell, and the spindle fibers break down.
• Meiosis one results in daughter cells with one replicated chromosome of each homologous pair.
• Daughter cells of meiosis are haploid cells.
• No chromosome replication occurs in-between meiosis 1 and meiosis 2.
• In prophase 2 the spindle apparatus forms, and the microtubules attach to the kinetochores.
• In metaphase 2 replicated chromosomes line up at the metaphase plate.
• In anaphase 2 sister chromatids separate and move to the opposite sides of the cell.
• In telophase 2 chromosomes finish their journey to the sides of the cell and the nuclear envelope develops, and the chromosomes decondense, and the spindle apparatus breaks down.
• In meiosis, one diploid cell gives rise to four haploid cells.
• As many as half of all conceptions are terminated because of problems in meiosis.
• If both sister chromatids more to the same daughter cell, this is called a nondisjunction.