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Fundamentals of Genetics Chapter 9 Genetics Goals • Be able to explain the relationship between genes, alleles, and traits • Be able to distinguish between a species’ genotype and phenotype • Be able to use a Punnett square to calculate the probability of each phenotype and genotype given a set of parents • Know the three laws of genetics 2-25-10 What is Genetics • Genetics is the scientific study of heredity. • Heredity is what makes each species unique. UMBUKU Lizard LIGER ZEEDONK Gregor Mendel - Austrian Monk, famous for his work with pea plants. known as the Father of Genetics chose traits that did not appear to blend was the first to follow single traits from generation to generation • trait - a specific characteristic that varies from one individual to another • true-breeding (purebred) plants - always produce offspring identical to themselves. • Hybrids - offspring from parents with different traits. • Alleles - different forms of a gene Genes – a short segment of DNA on a chromosome dthat contains the instructions for a single trait Molecular genetics – the study of the structure and function of chromosomes and genes The Principle of Dominance • Dominant alleles are always expressed – Ex: brown eyes are dominant. • 2 brown alleles = brown eyes • 1 brown allele and 1 blue allele = brown eyes • Recessive alleles are only expressed if both alleles are recessive – Ex: blue eyes are recessive • 2 blue alleles = blue eyes Segregation & Independent Assortment • The Law of Segregation – separation of alleles during meiosis to form gametes (sex cells). • The Law of Independent Assortment – genes for different traits can segregate independently during the formation of gametes. 2.26.10 gametes gene A a Homologous chromosomes A a gametes gene A A Homologous chromosomes A A • Homozygous – both alleles of a pair are alike (BB) – Purebred • Heterozygous – two alleles in the pair are different (Bb) – Hybrid • Genotype – genetic makeup (BB, Bb, bb) • Phenotype – physical characteristic (eyecolor, haircolor etc.) Students should use book here Genetic Generations • P generation – pure-bred parents are crossed • F1 generation – offspring of P generation selfpollinate • F2 generation – offspring of the F1 generation RR rr pollen Parental generation (P) pollen cross-fertilize true-breeding, purple-flowered plant true-breeding, white-flowered plant Rr First-generation offspring (F1) Punnett Squares • Monohybrid – only one characteristic is studied • Monohybrids have 2 possible phenotypes, 3 possible genotypes Punnett Squares – 1. 2. 3. Key: use a letter to represent each allele Cross: the genotypes of the parents. Punnet square Write the genotype: list all possible genotypes, then the fractions and percents shown in the Punnet square 4. Phenotypes: show all, with fractions and percents. Probability & Genetics • Probability is the likelihood that an event will happen. • used to predict the outcomes of genetic crosses • Penny – 2 possible outcomes 3.1.10 Dominant-Recessive Ex: RR = Red rr = White Rr = red - Dominant trait always shows up if present - Recessive trait only shows up if dominant trait is not present - Dom. trait is capitalized, rec. trait is lowercase - 3 genotypes, 3 phenotypes Trait Seed shape Seed color Pod shape Pod color Dominant form Recessive form smooth wrinkled yellow green inflated constricted green yellow purple white at leaf junctions at tips of branches tall (1.8 to 2 meters) dwarf (0.2 to 0.4 meters) Flower color Flower location Plant size Dihybrid Cross - Involves two pairs of contrasting traits Ex: color and shape for peas 3.4.10 Chapter 14: The Human Genome Pedigree • Circles – stand for females • Squares – stand for males • Colored circle or square – affected by recessive trait • Horizontal line – connects married couples • Vertical line with bracket – connects parents to children March 8 A Mutation is: A change in the nucleotide-base sequence of a gene or DNA molecule Examples: • Down syndrome: trisomy 21 • Klinefelter syndrome: XXY • albinism Mutations can be either unimportant or harmful