Chapter 2 - Chapter 2 Single-Gene Inheritance I Gene...

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Chapter 2: Single-Gene Inheritance I) Gene discovery—finding subset of genes in genome that influence a particular property A) Crosses: controlled matings B) Genetic dissection—use of mutants to ID a separate gene affecting that property C) Most direct way to get mutants is to visually screen a large # of individuals D) Each individual can be tested to see if it produces descendents in appropriate ratio for a mutation caused by a single gene II) Genome—organism’s unique and complete set of DNA A) Chromosomes—divided units of DNA located in the nucleus of each cell 1) Each chromosome has one molecule of DNA 2) # of DNA bands after electrophoresis=haploid chromosome # 3) DNA is packaged very efficiently in chromosome a) Wrapped around nucleosomes b) Each nucleosome composed of octamer of proteins (histones), which can affect gene regulation c) DNA-nucleosome chain is coiled and supercoiled 4) DNA and associated nucleosomes constitute chromatin (stuff of chromosomes) a) Chromatin varies in compactness along length of chromosome b) Dense chromatin (heterochromatin) near centromere c) Less dense chromatin is euchromatin 5) Nucleolar organizer—has multiple repeats of genes encoding ribosomal RNA 6) Nucleolus—contains ribosomal RNA, often attached to nucleolus organizer 7) Telomeres—tips of the chromosome 8) Genes are transcribed segments arrayed along the DNA of a chromosome a) Introns—noncoding regions, varies widely among species, humans have a lot of it making the genome very large b) Exons—coding sequences B) Diploid—contain two complete genomes—have two identical chromosome sets 1) Haploid number--# of chromosomes in the basic genome set (n) 2) Homologous chromosomes (aka homologs)—two members of a chromosome pair, usually not in a paired state 3) Gene pair—the two identical genes carried on the homologs C) Haploid—most species, only one set of chromosomes (incl. fungi and algae) III) Mendel’s law of equal segregation (aka Mendel’s first law)—in meiosis, the members of a gene pair separate equally into eggs and sperm A) Character trait/property—each has contrasting phenotypes (form taken by a character) B) Pure lines—all offspring produced in matings within members of a line are identical C) Genotypes—allelic combos underlining phenotypes D) Monohybrid—heterozygous for one gene E) Expected ratios for single-gene inheritance
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1) 1:1 for Y/y x y/y 2) 3:1 for Y/Y x Y/y 3) 1:2:1 for Y/y x Y/y IV) Mitosis—somatic cells divide to increase their number, programmed stage A)
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