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Download Biology Unit 5ish Notes: Mendelian Genetics
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Transcript
Biology Unit 5 Notes: Mendelian Genetics (1) Gregor Mendel • Monk • Studied genetics of pea plants. • He noticed that: – There were some traits which showed up all of the time (dominant). – There were some traits which showed up some times (recessive). – These traits are passed down from parents. – You can’t tell just by looking at an organism, which genes it has. (2) Dominant + Recessive Traits • Dominant Trait: – These will ALWAYS SHOW UP if they are present. – Representation Capital Letters • Recessive Trait: – These will ONLY SHOW UP if the organism inherited 2 together. – Representation Lower Case Letters (3) Inheriting Traits • You inherit 2 alleles for every gene. – Gene = Chunk of DNA. – Allele = Variation that chunk can come in. • “Heterozygous” = You inherited 1-Dominant and 1-Recessive allele. • “Homozygous” = You inherited 2 of the same alleles. – “Homozygous Dominant” = You inherited 2-Dominant alleles. – “Homozygous Recessive” = You inherited 2-Recessive alleles (4) Ways to Describe Inheritance • Phenotype: – Physical Description. – Examples: • “White” • “Brown” • “White and Brown Spotted” • Genotype: – Genetic Description. – Examples: • AA or Homozygous Dominant • Aa or Heterozygous • aa or Homozygous Recessive (5) What’s With These Letters? • The letters represent the alleles an organism can inherit. • You should choose letters with a different Capital + Lower Case appearance: – A and a – B and b – Bad Life Choices: S and s, X and x, C and c • Actual Letters DO NOT MATTER: – Heterozygous needs to be: Capital + Lower – Homozygous Dominant needs to be: 2 Capital – Homozygous Recessive needs to be: 2 Lower (6) What Are Punnett Squares? • Punnett Square = Tool used to make genetic predictions. • They do NOT tell you with certainty how many offspring will have which traits!!! • Tells you probability. – “There is a ¼ or 25% chance that the offspring will….” • SET-UP: – 1 Parent’s genotype on the top – Other Parent’s genotype on the side (7) Setting Up Punnett Squares • 1 Parent’s Genotype on the Top (doesn’t matter which one). • 1 Parent’s Genotype on the Side (doesn’t matter which one). • 1 Letter per Box! • For Example: – If one parent is AA and the other parent is aa… A A Draw your Punnett Square! a a (8) Filling In Punnett Squares • • • • They get filled in like a matrix-box OR like a grid on a map. The TOP letters copy down into each box. The SIDE letters copy across into each box. The dominant trait is always written in front. • For Example: – If one parent is AA and the other parent is aa… A A a Aa Aa a Aa Aa Draw your Punnett Square! (9) Interpreting Punnett Squares • Each Box = ¼ or 25% chance • For Example: – 4/4 Boxes have Aa, so… – There is a 4/4 or 100% chance that the offspring will be Heterozygous. – I could also say that there is a 100% chance that the offspring will look dominant. A A Aa Aa a Aa Aa a Draw your Punnett Square!