BIOL 118 Lecture Notes - Lecture 11: Sister Chromatids, Homologous Chromosome, Spindle Apparatus
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13 Mar 2017
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Centrosomes replicated: meiosis 1, purpose: separate the homologous chromosomes into daughter cells, daughter cells are haploid, early prophase 1. Synapsis occurs: homologous chromosome pairs come together: pairing called a bivalent of the two homologs, late prophase 1. The homologs begin to separate: chiasma- points where the non-sister chromatids stay attached to each other. The paired homologs (bivalents) line up along the metaphase plate: each bivalent moves independently, alignment of maternal and paternal homologous chromosomes is random, anaphase 1. The paired homologs separate and migrate to opposite ends of the cell: telophase 1. Homologs migrate to the poles of the cell. Daughter cells contain one homolog of each chromosome (haploid: meiosis 2, each daughter cell is haploid, no chromosome replication takes place, purpose: separation of sister chromatids, consists of 4 continuous steps, prophase 2. Replicated chromosomes (consisting of 2 sister chromatids) line up at the metaphase plate: anaphase 2.
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Which statements pertaining to genetic variability are correct? Check all that apply (note that wrong answers will be deducted from right answers)!
Crossing over is defined by the exchange of chromosome pieces during metaphase one of meiosis. |
If a germ cell (i.e. parent cell before meiosis) had only two pairs of homologous chromosomes (i.e. 4 chromosomes total) there are 2 possible combinations of maternal and paternal chromosomes in gametes. |
Siblings produced by sexual reproduction are different because sperms are different from one another and eggs are different from one another, and the combination of an egg and sperm is basically unique. |
Random fertilization means that all possible combinations of eggs and sperm are equally likely, i.e. it is pure chance which sperm fuses with which egg. |
Individual chromosomes contain thousands of genes. This means that during each crossing over event, more than one gene is exchanged between paternal and maternal chromosomes. |