Study Guide Test 4

Study Guide Test 4 - Test #4 Chapter 2 (Single Gene)...

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Chapter 2 (Single Gene) Diploid/Haploid o In diploid, homologous chromosomes contain almost identical DNA o Haploid easier to manipulate; phenotype directly expresses genotype Organization: DNA nucleosomes chromatin chromosomes o Centromere: dense chromatin near it Dense: heterochromatin Less dense: euchromatin o Nucleolar Organizer: repeats encoding rRNA o Telomeres: Tips of chromosomes Law of Equal Segregation: members of a gene pair separate equally into the eggs and sperm during gamete formation in meiosis. Heterozygote for one gene sometimes called monohybrid F1: 3:1 phenotype but 1:2:1 genotype Meiosis occurs only in diploid cells o 2n n + n + n + n S Phase of mitosis: DNA replication producing pairs of identical sister chromatids Meiosis forms 4 homologous chromatids; they join through synapsis relying on the synaptonemal complex o Replicate sister chromosomes are called a dyad o The unit of the pair of synapsed dyads is a bivalent o The four chromatids that make up a bivalent are called a tetrad. Crossing over occurs in tetrad stage Meiosis: At start, 2 homologs; at replication, 2 dyads; at pairing, a tetrad; at first division, one dyad to each daughter cell; at second division, one chromatid to each daughter cell o A/a example: At start, 1 homolog with A, 1 with a; at replication, one dyad AA and one dyad aa; at pairing, tetrad is A/A/a/a; at first division, one cell is AA, the other aa; at second division, four cells, two of A, two of a o ½ chance of A, ½ chance of a To directly show DNA segregation, brute force method (sequence in the meiotic products) and restriction fragment length polymorphism (mutants can chance target sites to change size of bands that are equally segregated) o Analyzed under southern blot; those with 1 band are homozygous wild, those with 2 bands are homozygous recessive, and those with 3 bands are heterozygous Gene sites and mutations: null, leaky, silent Haplosufficient: recessiveness is observed in mutations in genes that are functionally haplosufficient; one haplosufficient gene provides enough geneproduct to carry out normal transactions Haploinsufficient: a null mutant allele is dominant because in a heterozygote, the single wild-type allele cannot provide enough product for normal function. Molecular force of segregation is the spindle (polymers of protein tubulin)
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Study Guide Test 4 - Test #4 Chapter 2 (Single Gene)...

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