BIOL 190 Lecture Notes - Lecture 18: Tay–Sachs Disease, Homologous Chromosome, Gamete

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20 Apr 2017
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Gene- segment of dna at at particular location on a particular chromosome- codes for a specific protein. Allele- a unique version of a gene. Different alleles for the same gene differ by at least one nucleotide. We use different formats (upper and lower case) of the same letter for different alleles of the same gene- h,h. H= allele for non functioning or no enzyme. New alleles arise when mutations occur in existing alleles. Dominant alleles- (uppercase)- always show up in phenotype if present. Example- 2 unaffected parents- heterozygotes (carriers) for tay sachs disease- hh. Recessive alleles (lowercase)- will be masked/ hidden by dominant allele if both are present. Only show up in phenotype if homozygous. Example- children affected by tay- sachs, hh. Phenotype- appearance or characteristic that results from the expression of the alleles in the genotype. Examples- tay sachs disease, brown hair, color blindness. Genotype- combination of alleles present in a diploid cell/ organism.

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