Classical Genetics The “Old School” way of heredity! Eckert – Minerva DeLand Science Vocabulary P generation (parent) 1st group crossed F1 generation (first filial) offspring of parent generation F2 generation (second filial) offspring of F1 Vocabulary Hybrid Offspring of two pure parents ex. BB x bb = Bb hybrid Vocabulary Dominant A trait that, when present, expresses itself Recessive A hidden trait Vocabulary Gene Carried by chromosomes in a definite order 2 genes are needed to express a trait Vocabulary Chromosomes Found in nucleus Hereditary information Vocabulary Alleles Different copies or forms of a gene controlling a trait Vocabulary Homozygous Alleles for a trait are the same Heterozygous Alleles are different Vocabulary Genotype Genetic makeup of an organism Phenotype The physical trait that an organism develops as a result of its genotype (tall, short, etc) Gregor Mendel Investigated inheritance with pea plants Developed principles that are still accepted today Mendelian Laws and Genetic Principles Law of Dominance When an organism is hybrid Only the dominate trait is expressed TT = Tall Tt = Tall tt = short Law of Segregation Individuals are controlled by a pair of genes Pairs of genes are separated from each other during meiosis and recombine at fertilization The Gene-Chromosome Theory Genes make up chromosomes Arranged in definite order (like beads on a necklace) The Law of Probability Chance Several possible events that might happen will occur in equal numbers over a large number of trials Principle of Independent Assortment During meiosis, genes from different traits are separated and distributed to gametes independently of one another Pedigrees Heredity in humans cannot be studied the same way as in plants and animals for 3 reasons 1. Time between generations is too long 2. # of offspring is too small 3. No controlled experiments are possible Pedigrees One can learn genetic traits in humans by tracing the appearance of these traits in families over several generations by using a pedigree chart. This is a diagram that shows the presence or absence of a particular trait in each member of each generation.
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