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Polygenic traits when one trait is governed by mulple

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Unformatted text preview: otype (physical expression) •  On the lef, is the eye s phenotypes of green and black eye genes. •  Two organisms whose genes differ at one locus are said to have different genotypes. •  A locus (loci for plural) is the specific [email protected] of a gene of a DNA sequence on a chromosome. •  A variant of the DNA sequence at a given [email protected] is called a allele. •  The ordered list of loci known for a [email protected] genome is called a gene4c map. Diploid and polyploid cells whose chromosomes have the same allele of a given gene at some locus are called homozygous, with respect to that gene (otherwise, it is heterzygous). The chromosomal locus of a gene might be wrigen "6p21.3” •  6: chromosome number •  p: [email protected] on the chromosome’s short arm (“p”) or long arm (“q”) •  21.3: the [email protected] on the arm: region 2, band 1, sub ­ band 3. The bands are visible under a microscope when the chromosome is stained. Genotype/Phenotype Phenotype: Blue eyes Brown eyes Genotype: Recessive: bb Dominant: Bb or BB •  Pleiotropy: when one gene affects many different traits. •  Polygenic traits: when one trait is governed by [email protected] genes, which maybe on the same chromosome or on different chromosomes. –  The [email protected] effects of numerous genes on a single phenotype create a [email protected] of possible outcomes. –  Polygenic traits are also most [email protected] to environmental influences. Pleiotropy in humans: Phenylketonuria (PKU): A disorder that is caused by a deficiency of the enzyme phenylalanine hydroxylase, which is necessary to convert the [email protected] amino acid phenylalanine to tyrosine. A defect in the single gene that codes for this enzyme therefore results in the [email protected] phenotypes associated with PKU, including mental retarda...
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