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NATS 1690 (39)


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Natural Science
NATS 1690
Barbara Czaban

Mendel’s second experiment with pea plants – Two traits - Each pair of alleles segregated into gametes independently of other pairs of alleles - In theses series of crosses, he followed the inheritance of two different characters and dihybrid crosses  To determine if different traits were inherited as a unit or independently - His results led to “Law of independent assortment”  Alleles for one trait passed to offspring independently, without affecting the segregation of alleles for another trait Law of Independent Assortment - When sperm with 4 classes of alleles and ova with 4 classes of alleles combine there are 16 equally probable ways in which the alleles can combine in the F2 generation - These combinations produce 4 distinct phenotypes in a 9:3:3:1 ratio - This ratio was consistent with Mendel’s actual results - Based on predictions from two-trait and dihybrid crosses The relationship between genotype and phenotype - Each character was controlled by a single gene - Each gene had only two alleles – one of which is completely dominant to the other - The genes of the traits he studied were each on separate chromosomes - Would not of been able to formulate his laws if he had been working on the same chromosome Phenotypic traits - Incomplete dominance - Pleiotropy – Single gene  Multiple traits - Polygenic inheritance – Multiple genes  Single trait (skin color) - Multiple alleles - Codominance - Epistasis - Environmental influences Incomplete Dominance - When one allele of a pair is not fully dominant over its partner - The heterozygote’s phenotype is somewhere between the homozygotes - Clear example is seen in flower color of snapdragons - Red-flowered X White-flowered (P-ge
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