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Transcript
Genetics Genetics Vocab • Genetics: the scientific study of heredity • Heredity: passing of traits from generation to generation • • Traits: specific characteristics that vary from individual to individual Genetics Vocab • Genes: segment of DNA that carries the instructions for making traits • Alleles: different forms of a trait (we will use letters to represent the different forms) – Example: • Trait: hair color • Alleles would be: – Blonde – Brown – Black – Red – And any combination in between Genetics Vocab • Dominant trait: the trait observed when at least one dominant allele for a characteristic is inherited • Recessive trait: a trait that appears only when 2 recessive alleles for the same characteristic are inherited Genetics: The Science of Heredity - Mendel’s Work Dominant and Recessive Alleles Mendel studied several traits in pea plants. Genetics Vocab • Genotype: the inherited combination of alleles (TT, tt, or Tt) • Phenotype: an organisms physical appearance (Tall, short) Genetics Vocab • Homozygous: 2 alleles are the same for a trait (TT or tt) • Heterozygous: 2 alleles are different for a trait (Tt) Mendel • Austrian monk who studied genetics in pea plants • How Mendel did his work: – By cross-pollinating plants by transferring pollen from one plant to the egg cells of another – He crossed a pair of plants with different alleles for a trait Genetics: The Science of Heredity - Mendel’s Work Crossing Pea Plants Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this. Genetics: The Science of Heredity - Mendel’s Work Mendel’s Experiments In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants. Punnett Squares • a table that shows all the combinations of alleles that might result from a genetic cross • Vocab you will need to remember in order to do a punnett square – Alleles, dominant, recessive, homozygous, heterozygous, phenotype, and genotype. Genetics: The Science of Heredity - Probability and Heredity A Punnett Square The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele. Genetics: The Science of Heredity Genotypes and Phenotypes Genotypes: ¼ RR 2/4 or ½ Rr ¼ rr Phenotypes: ¾ Round ¼ Wrinkled