Lecture 3 Guide

Lecture 3 Guide - DNA molecules replicate to form identical...

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Unformatted text preview: DNA molecules replicate to form identical chromatids Chromosomal DNA is wrapped around histones Stages of Mitosis Stages of Meiosis Synaptonemal complexes at meiosis MITOSIS Phase: Interphase diploid chromosomes decondensed DNA synthesis in S phase two copies of diploid chromosomes condense sister chromatids visible ----- * chromosomes line up on equator -----sister centromeres split chromatids move to opposite poles ------ MEIOSIS I reductional division MEIOSIS II equational division diploid chromosomes decondensed DNA synthesis in S phase two copies of diploid chromosomes condense sister chromatids visible homologs pair and recombine ---------homologous pairs line up on equator ---------------homologs move to opposite poles two copies of haploid in each cell occurrence of interphase varies --------two copies of haploid chromosomes condense sister chromatids visible -------chromosomes line up on equator ------sister centromeres split chromatids move to opposite poles ------- Prophase Metaphase Anaphase Telophase nuclear envelope reforms, chromosomes decondense, cytokinesis two genetically identical diploid cells occurrence of telophase varies cytokinesis two non-identical cells, each has two copies of haploid nuclear envelope reforms, chromosomes decondense cytokinesis four non-identical cells, each has one copy of haploid End result * Recombination can occur during mitosis. Mendel's 1st Law - The law of (equal) segregation. The two members (alleles) of a gene pair segregate from each other into the gametes (egg and sperm/pollen), so that one-half of the gametes carry one member (allele) of the pair, and the other half of the gametes carry the other member (allele). The Five Postulates of Mendel 1) Hereditary determinants are particulate in nature (i.e., non blending). We now call these determinants genes. 2) Each adult plant has two hereditary determinants. Adults carry two alleles of each gene. From the F1 appearance, Mendel reasoned that one determinant can be dominant to another. 3) The two hereditary units separate equally from each other during gamete formation. As a result of meiosis, half the gametes receive one allele of a gene pair, and half receive the other. 4) Gametes unite at random Gametes carrying one allele show no preference in combining with other gametes. 5) During gamete formation, the segregation of alleles of one gene is independent of the segregation of alleles of another gene* (*unless close together, or linked, on same chromosome) Genetic analysis begins with mutants: the seven phenotypic pairs studied by Mendel Cross-pollination and selfing are two types of crosses A single-gene model explains Mendel’s ratios Single-gene inheritance tracked at the DNA level Sex Drosophila: Ratio of X:Autosome female: XX, XXY male: XY, XO, XYY Humans: Presence of Y chromosome female: XX male: XY How is X equalized? Male X is twice as active as one X in female. X inactivation: one female X is inactivated, Barr body An example of X-linked inheritance An example of X-linked inheritance Pedigree symbols Inheritance of an autosomal recessive disorder Inheritance of an autosomal recessive disorder Inheritance of an autosomal dominant disorder Inheritance of an autosomal dominant disorder Inheritance of an X-linked recessive disorder Inheritance of an X-linked recessive disorder Inheritance of an X-linked dominant disorder Inheritance of an X-linked dominant disorder * Draw mitosis for three pairs of chromosomes. Label the chromosomes with the loci A/a; B/b; G/g. * Draw meiosis for three pairs of chromosomes. Label the chromosomes with the loci A/a; B/b; G/g. ...
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