GEOG 170A1 Lecture Notes - Lecture 10: Chromatin, Melanin, Meiosis
20 Sep 2015
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Document Summary
An allele is dominant if its effect masks the effect of a recessive allele paired with. Mendel focused on traits based on clearly dominant and recessive alleles. 2 non-identical alleles of a gene are both expressed in heterozygotes. 1 allele is not fully dominant over its partner. The heterozygote s phenotype is somewhere between the 2 homozygotes. The environment affects the expression of many genes, which affect phenotype. Environment driven changes in gene expression patterns can be permanent. Such changes are implemented by gene controls, such as chromatin modifications and rna interference that act on dna itself. Temperature changes and the length of a day affect melanin production and other pigments that color skin and fur. Genetically identical yellow plants grow to different heights of different altitudes. Many traits do not appear in distinct forms. Variations in skin color may have evolved as a balance between vitamin d. Single genes on autosomes or sex chromosomes govern more than 6,000 possibilities.
