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Heredity • The genetic passing of characteristics (traits) from parent to offspring – Hereditary traits are determined by specific genes – Genes are on chromosomes What cells pass on genetic information? gametes! Offspring looking like their parents Alleles Two alleles for every gene Alleles • Alleles are on chromosomes • Alleles for the same trait are found in the same location on homologous chromosomes • One chromosome can carry hundreds of alleles Chromosomes carry alleles Complete dominance • Alleles: dominant or recessive – Dominant alleles will overpower recessive alleles in appearance • Represented by a CAPITAL letter – Recessive alleles will stay masked by dominant alleles in appearance • Represented by a lowercase letter Genetics: complete dominance • Pea plants: Purple flowers are dominant over white flowers • This trait (color) is governed by only two alleles • Purple is represented by P • White is represented by p Homozygous traits vs heterozygous traits PP Pp p p Homozygous vs Heterozygous • Homo: same • Hetero: different • Homozygous dominant: PP • Homozygous recessive: pp • Heterozygous: Pp Genotype vs Phenotype • Genotype: genetic makeup, what type of alleles are present in the cell • Phenotype: the outward physical appearance from the alleles • Lets go back and look at flowers Genotype Phenotype Homozygous or Heterozygous PP Homozygous dominant Pp heterozygous pp Homozygous recessive Gregor Mendel • 1822 –1884 was an Austrian monk and scientist • “father of modern genetics” – groundbreaking work on theories of heredity • Used pea pod plants Mendels experiment with flower color Do Now: 1/12/12 (made up example!) The color red in flowers is dominant over the color yellow. •What letters would you use to represent these alleles? •What is the genotype of a flower that is homozygous dominant? Heterozygous? Homozygous recessive? •What is the phenotype of a flower that is homozygous dominant? Heterozygous? Homozygous recessive? Do Now continuation: A heterozygous red flower crossfertilizes with a yellow flower. What are the possible genotypes for the offspring? Complete dominance practice Suppose black noses are dominant over pink noses in a certain breed of dogs. A homozygous dominant black-nosed dog is bred with homozygous recessive pink-nosed dog. •Genotype of each parent? •What is the genotypic ratio? •What is the phenotypic ratio? •What percentage of the F1 generation will have a heterozygous genotype? •What is the probability that the 5th puppy will have a pink nose? Complete dominance: going backwards Use the dog example from the previous slide: A litter of puppies was born! Out of the 6 puppies4 have black noses and 2 had pink noses. •What were the genotypes of the parents? QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Dihybrid punnett squares QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Dihybrid punnett square Circle is dominant-C Square in recessive- c Black is dominant- B White is recessive- b Cross: C c B b x C c B b