Chromosomes Before Meiosis Chapter 1 Study Guide
• Meio'is lead< to independent a,o,tnoent of chromo,ome< a9":f!.compo,ition of alleles in daughter eel/, o Chromosomes replicate in interphase before meiosis
• Interphase: ·
• Active period that precedes meiosis and includes preparation for cell division .
• DNA replicated in the "S" Phase of interphase
• This results in chromosomes having two identical DNA strands
• Genetically identical strands are called sister chromatids
• Held together by a centromere located at the center
• Chromatids separate during meiosis II
• They become independent chromosomes with each one ofthem made of a single DNA strand
• If DNA didn't take place before meiosis, there would be no need for 2nd meiotic division
• Meiosis I: Diploid to haploid
• DNA replication
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• Two haploid daughter cells are formed o Sister chromatids separate in meiosis ll
• Second division that separates sister chromatids
• Chromatids may not be identical due to crossing over in prophase I • Chiasmata formation between non-sister chromatids results in the exchange of alleles
o Crossing over is the exchange of DNA material between non-sister homologous chromatids
• When chiasmata is formed between the bivalents in prophase I, DNA is exchanged between the non-sister homologous chromatids
• Crossing over results in production of new allele combination on the chromosomes
• Recombinant chromosomes consist of genetic material from both homologues o Crossing over produces new combinations of alleles on the chromosomes of the haploid cells
• Genes may be linked or unlinked and are inherited accordingly o Gene loci are said to be linked if on the same chromosome
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• Linkage group is a group of genes whose loci are on the same chromosomes and don't independently assort
• Linked genes tend to be inherited together
• Don't follow the normal dihybrid cross
• Phenotypic ratio is more closely assigned to monohybrid cross as two genes are inherited in a single unit
• Linked genes may become separated through
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