Chapter 2 - Chapter 2: Single-Gene Inheritance Mutants...

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Chapter 2: Single-Gene Inheritance Mutants – individual organisms having some altered form of a normal property. Each gene discovery project begins with a hunt for mutants affecting the biological process that is the focus of the research. The genetic approach to understanding a biological property is to discover the genes that control it. o One approach to gene discovery is to isolate mutants and check each one for single-gene inheritance patterns (specific ratios of normal and mutant expression of the property in descendants). Single-gene inheritance patterns are useful in applied genetics as well. Many human disorders such as cystic fibrosis and tay-Sachs disease, are inherited as a single mutant gene. o After a key gene has been defined in this way, geneticists can zero in on it at the DA level and try to decipher the basic cellular defect that underlies the disease, possibly leading to new therapies. 2.1 Genes and Chromosomes Genome – an organism’s unique and complete set of genetic information (DNA). In eukaryotes, the bulk of the DNA of a genome is found in the nucleus of each cell. The chromosome set resent in organisms from the same species has a characteristic chromosome number and appearance. Diploid – means containing two complete genomes, and two identical chromosome sets Haploid – the number of chromosomes in the basic genomic set. Many species, forming the bulk of eukaryotic biomass on the planet, are normally not diploid but haploid (containing one set of chromosomes). o Examples of haploid organisms: Fungi and Algae
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Simple calculations on the amount of DNA per cell show that the length of a DNA molecule in a chromosome is much greater than the length of the chromosome. Nucleosome – wrapping the DNA around molecule spools o Each nucleosome is composed of an octamer of proteins called histones Dense chromatic is called heterochromatin, and less dense is called euchromatin. Nucleolar organizer – a unique region (usually on one specific chromosome) that
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Chapter 2 - Chapter 2: Single-Gene Inheritance Mutants...

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