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CHAPTER9 - Chapter 9 Patterns of Inheritance I Genetics A...

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Chapter 9: Patterns of Inheritance I. Genetics A. Science that attempts to explain the mechanisms that account for hereditary relationships B. Beginnings of modern genetics was with the experiments of an Austrian monk, G regor Mendel , during the late 1800’s C. Mendel used garden pea plants to determine that hereditary characteristics are carried and transmitted by factors ( note: these are now known as genes ) D. Mendel suggested that genes occur in pairs - the male parent contributes 1 gene and the female parent contributes the other II. Genetic Vocabulary A. Alternative forms of a gene, known as alleles , occur at the same position or locus on homologous chromosomes B. Prior to Meiosis, the chromosomes are duplicated during interphase, resulting in homologous pairs of chromosomes C. During Meiosis, the alleles are separated from each other and each gamete receives 1 allele of each pair (Mendel’s Law of Segregation) D. After fertilization: 1. If the two alleles for a given trait are the same , the organism is said to be homozygous for that trait 2. If the two alleles are different , the organism is said to be heterozygous for that trait E. An allele may be designated as dominant or recessive 1. Dominant alleles are denoted by capital letters 2. Recessive alleles are denoted by lower case letters 3. Typically, the dominant allele covers up or masks the trait carried by the recessive allele (Mendel’s Law of Dominance) F. There are three possible combinations of two alleles in a pair: 1. Homozygous dominant -_____ 2. Homozygous recessive -_____ 3. Heterozygous -_____ G. The outward appearance of an organism (hair color, freckles, etc...) is known as the phenotype H. The genetic composition of organisms (AA, Aa, aa) is its genotype III. Monohybrid cross - inheritance of a single trait A. Example: flower color B. The allele R = red and r = white C. Problem: Cross a homozygous red flowered plant with a homozygous white flowered plant 1. A punnett square is used to predict the possibilities of the offspring 2. The resulting offspring possibilities are known as the first filial generation or F 1 generation
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Chapter 9 page 2 D. Problem: Cross two of the first generation flowers with each other
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