BIOL 1090 Lecture Notes - Lecture 3: Ascospore, Sister Chromatids, Dna Replication
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12 Oct 2016
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N number of chromosomes = the haploid state. Sister chromatids (two chromatids in a pair) are homologous chromosomes . Comparing between two chromosomes from two different pairs is called heterologues : eg: one chromatid from pair 2, one chromatid from pair 3\ Prophase i: chromosomes begin to condense, homologous chromosomes begin to pair, homologous chromosomes are fully paired, homologous chromosomes separate, except at chiasmata. Pairing of homologous chromosomes is called synapsis and is often facilitated by formation of a synaptic complex. Pachynema- homologous chromosomes are fully paired: bivalents or tetrads (four chromatids) Crossing over involved breakage of chromatids and the exchange of the broken pieces between homologous chromosomes (non-sister chromatids) (fig. 2. 11: after crossing over, homologous chromosomes start to pull apart, but remain joined at the cross over junctions (chiasmata) Now we have an intact maternal chromatid, a hybrid maternal chromatid, a reciprocal hybrid paternal chromatid, and an intact paternal chromatid.
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