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How are characteristics passed down through generations? • Inheritance – characteristics are passed through generations by genetic material (traits) How Do We Know? Gregor Mendel - discovered the pattern of inheritance by studying pea plants. What did Mendel discover? The Principle of Segregation 1) Inherited traits are determined by distinct units named genes 2) Each gene carries two factors, one inherited from each parent (alleles) 3) The two alleles separate from each other and end up in gametes during meiosis. Largest Size NUCLEUS Contains CHROMOSOMES Contains GENES Interaction between two ALLELES Made of DNA SMALLEST size Largest Structure: • In each of our cells (except or gametes) we have 23 pairs of chromosomes • One member of the chromosome pair comes from our father, the other from our mother. Karotype How are genes arranged on chromosomes? • Genes are regions of DNA within the chromosome pair that code for a particular trait. • Each gene is made up of two factors, one from each chromosome pair. • These factors are called alleles Are an individual's alleles the same? homozygous • The two alleles that make up each gene may be the same or different. • If the alleles are the same they are called homozygous • If the alleles are different they are called heterozygous heterozygous How do alleles determine the trait of an individual? • Each trait is determined by the interaction between the two alleles of a gene and several interactions are possible. • The genetic make up of a trait= genotype • The physical appearance of a trait= phenotype 1. Complete Dominance – when one allele completely masks the other. Dominant Alleles – only one allele needed to express trait. Recessive Alleles – need two recessive alleles for trait to be expressed. Ex: Y = yellow y= sugary Recessive trait : Sugary kernels are recessive Dominant trait: Genotype= Genotype= Phenotype= Phenotype= Yellow kernels 2. Incomplete dominance When the alleles are blended and the offspring have a mix of their parent traits. ex. Snap Dragons R = red r = white Offspring can be pink! Heterozygous genotype 3. Codominance – in this case both alleles are expressed. BB= black corn YY= yellow corn BY = black and yellow corn Genotype codes for phenotype • GENOTYPE - the two letters that represent the alleles of a gene EX. RR, Rr, rr • Phenotype - the outward appearance of an organism (what it looks like) Ex. If a farmer has a red flower (RR) - the genotype is RR - the phenotype is red 1. A brown dog (bb) bb the genotype ________ brown the phenotype _______ 2. A long haired cat (Hh) the genotype _______ Hh Long haired the phenotype _______ 3. A spotted owl (SS) SS the genotype _____ spotted the phenotype _____ (Review) • Remember The Principle of Segregation? • Mendel learned that the alleles of each individual seperate and end up in gametes (meiosis) • Ex. A female pure brown dog (bb) bb b b PRACTICE 1. A hybrid male yellow canary (Yy) Yy 2. A pure female white flower (rr) rr If a male red flower (Rr) and a pure white flower from above got their gametes together (fertilization ) what kind of combinations could be formed? X • Male red flower (Rr) • Female white flower Rr Sperm 1 rr Sperm 2 Egg 1 Egg 2 Genotype + 1 = 1 + 1 2 2 2 + = = 1 + 2 = Phenotype