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Heredity Test 3 - Mendel's First Law What rules dictate...

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Mendel’s First Law What rules dictate inheritance of traits? Theories of Inheritance o Blending theory of inheritance: traits blend together from generation to generation (each allele contributes to the phenotype) o Dominance: one trait is “stronger” than the other Key Points: o Pea plants and many organisms are diploid (2n) o In many cases, one trait is stronger than another o Different alleles of the same gene segregate during meiosis I The father of genetics: Gregor Mendel o At the time, he was unaware of: Mitosis/meiosis Chromosomes/copy # (ploidy) Genes/alleles Important: o In all non-sex human cells, there are two copies of each chromosome (one from mother, one from father) o Gene: sequence that codes for protein o Allele: alternative version of a gene o Heterozygous: 2 different alleles o Homozygous: same alleles Mendel analyzed 7 traits of flowering pea plants o Utilized homozygous pea plants (true-breeding) Monohybrid cross (test one trait at a time) o Parental generation: Tall (T) + short (t) o F1: Tall (T), non true-breeding o F2: TTTt (3:1 phenotypic ratio) Mendelian logic: o Particulate factors (genes) carry genetic information o One of two traits was masked in the F1 generation (dominance) Law of segregation o Masked (recessive) traits in F1 generation reappear in F2 o Two copies of a gene (alleles) segregate/separate during transmission Recessive traits in humans o CC: homozygous dominant, curly hair o Cc: heterozygous carriers, curly hair o cc: homozygous recessive, straight hair Mendel’s two factor (trait) crosses o Mechanism for inheritance of two traits? Key Points: o Mendel’s 2 nd Law: inheritance of one trait does not affect another o Law is valid in many cases, but not when the genes are on the same
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chromosome (linkage) Linkage: certain associations between 2 genes (RY, ry always) Independent Assortment: no physical association Mendel’s Second Law: Law of Independent assortment o Two different genes will randomly assort alleles during gamete formation o
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