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Warm up (in ISN): • One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits (ss). Use a Punnett square to determine the probability of one of their offspring having long hair. Practice 2: • In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? Practice 3 • A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? Practice: • A purebred red cow (R) is crossed with a purebred white cow (r). Draw a Punnett Square depicting this cross, and write down the genotypic and phenotypic ratios resulting form this cross. This is actually the phenotype for heterozygous roan cows! Alternative Patterns of Inheritance • Not every trait works out perfectly-that is, one trait is dominant, one recessive • Exceptions to Mendel’s principles (one dominant, one recessive) Co-dominance • Pattern of inheritance where both alleles are dominant and therefore both phenotypes are expressed – Usually shown by two capital letters – Example: roan cows, chicken feathers Co dominance Practice: • In a certain fish, blue scales and red scales are codominant. When a fish has the genotype BR, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales. Incomplete Dominance • Incomplete dominance-one allele is dominant to another only to a certain extent, so it can’t completely express its phenotype – This results in phenotypes that are intermediate – Example: snap dragons: Incomplete/co Dominance Practice: • Cross one white and one pink snapdragon. Give phenotypic and genotypic ratios. (incomplete dominance) • Cross one white chicken and one chicken who has black/white feathers. Give phenotypic and genotypic ratios (co-dominant) • Cross two red/white cows Multiple alleles • When there are more than two forms of one gene • Ex: Blood type, A B and O forms Note-this is also an example of what type of inheritance? Multiple Alleles practice: • Mom has type O blood. Dad has type AB blood. What percentage of their kids will inherit type B blood? Polygenic traits • When a trait is controlled by one than one gene • For example eyecolor-look around – Not just blue, green, brown, varying degrees Eye color Genes and the environment • Environment can influence expression of genes – Genes contain information, environment can determine how much of that information is expressed – Example: Western white butterflies, Siamese cats Closure: • Go back to warm up problem. Using what you learned about co-dominance, fix your genotypic and phenotypic ratios-hand into me before you leave Alien Genetics • You are to create your own species of Alien. For your alien, you must create 3 traits – One trait must show normal dominant/recessive relationships – One must be co dominant – One must be incompletely dominant • Cross two purebred individuals showing the different forms of these characteristics and the resulting hybrid offspring – Draw a Punnett square for each cross – Draw each organism, showing the traits