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HEREDITY, GENES & DNA ENDURING UNDERSTANDINGS * Heredity is the passing of traits from parents to offspring. * DNA is a double helix made up of nucleotides. * A gene is a set of instructions for a specific trait. * Meiosis is the reproduction of sex cells. Try Human Wheel using Handout Inherited Characteristics (40) MENDEL & HEREDITY Heredity is the passing of traits from parents to offspring. Gregor Mendel studied pea plants to see how traits pass from parent to offspring. Mendel compared the offspring of true-breeding and cross-pollinated plants. True-breeding plants are self-pollinated and produce offspring exactly like the parent. Cross-pollination produces a combination or variety of traits from the parents. DOMINANT VS RECESSIVE TRAITS A dominant trait is a trait that appears in the offspring. A recessive trait is a trait that does not appear in the offspring. Mendel's Ratios compare the number of dominant traits with the number of recessive traits. Probability is the mathematical chance that an event or trait will occur. insert B7 Quicklab (paper copy) Genetic Variation in the Classroom GENES, ALLELES & PUNNETT SQUARES A gene is a set of instructions for a specific trait. Offspring inherit 2 sets of genes, 1 from each parent. These combinations of 2 different forms of the same gene are called alleles. A genotype is the combination of inheritated alleles. A phenotype is the appearance of a genotype. HOMOZYGOUS ALLELES Homozygous alleles have either both dominant or both recessive genes. HETEROZYGOUS ALLELES Heterozygous alleles have 1 dominate gene and 1 recessive gene. Punnett Squares use parent alleles to construct a diagram showing all possible phenotypes for a particular trait. Write the alleles and fill in the Punnett squares for ... C can curl tongue, c cannot curl. C C C C C C c C One parent has homozygous dominant alleles, one parent has heterozygous alleles. Both parents have heterozygous alleles. Problem Consider a cross between a pea plant that is heterozygous for round seeds and a pea plant that has wrinkled seed. The allele for round seeds is dominant (R) over that for wrinkled seeds (r). Determine the genotypes of the offspring and indicate both the genotypic and phenotypic ratios. Let statements: Let R represent the dominant allele for round seeds. Let r represent the recessive allele for wrinkled seeds. P generation: Rr X rr Punnett Square: Activity 1) Monohybrid Problems 3C / Dihybrid Problem 3U 2) Breeding Pigs Taking it one step further.... Often in genetics the question comes up whether the inheritance of one trait would affect the inheritance of another trait? For example if flower colour is governed by flower height? In order to answer such a question we introduce Di hybrid Crosses - is a cross between two parents that breed true for different versions of two traits Lets revisit the example above.... Flower colour is governed by gene P Flower height is governed by gene T Let P represent the dominant allele for pink colour Let p represent the recessive allele for white colour Let T represent the dominant allele for tall height Let t represent the recessive allele for short height If we crossed a homozygous pink & tall flower with a homozygous white & short flower our punnet square would look like this. PPTT X Alleles assort independently PT PT PT PT pt pt pt pt pptt PT pt pt pt pt PT PT PT All F1 generation have the same genotype & phenotype PpTt (Pink & tall). However, we are still not sure whether the alleles for colour and height were inherited together or if they segregated independently. Further crossing is required. We need F2 PpTt X PpTt During Meiosis Alleles assort independently PT Pt pT pt PT Pt pT pt P - pink T - tall p - white t - short PT Pt pT PT Pt pT pt pt Conclusion Genes that segregate independently in meiosis do not influence each others inheritance Practice Problems #1~3 pg. 136