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GENETICS AND INHERITANCE

GENETICS AND INHERITANCE. CHAPTER 19. Alleles. Different forms of homologous genes: humans have 23 pairs of chromosomes Homozygous : both alleles identical Heterozygous : alleles different Genotype : complete set of genes and alleles Phenotype : observed physical and functional traits.

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GENETICS AND INHERITANCE

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  1. GENETICS AND INHERITANCE CHAPTER 19

  2. Alleles • Different forms of homologous genes: humans have 23 pairs of chromosomes • Homozygous: both alleles identical • Heterozygous: alleles different • Genotype: complete set of genes and alleles • Phenotype: observed physical and functional traits

  3. Punnett Squares Figure 19.2

  4. Patterns of Genetic Inheritance • Punnett square analysis: predicts patterns of inheritance • Mendel developed basic rules of inheritance • Law of segregation: reproductive cells carry only one copy of each gene • Law of independent assortment: genes for different traits are separated from each other independently during meiosis; applies in most cases

  5. Allelic Interactions • Genotype and environment affect phenotype • Dominant alleles: gene always expressed, even if heterozygous • Recessive alleles: two copies of gene needed to be expressed, must be homozygous • Incomplete dominance: heterozygote is an intermediate phenotype

  6. Allelic Interactions (cont.) • Codominance: both phenotypes equally expressed • Polygenic inheritance: multiple genes involved • Linked genes: may be inherited together if close on a chromosome

  7. Pedigree Chart: Inheritance Pattern for an X-linked Recessive Disease Figure 19.12

  8. Sex-Linked Inheritance: X and Y Chromosomes • Origin of sex chromosomes • Chance mutations • Y determines sex • Sex-linked genes located on sex chromosomes • Sex linked or X-linked inheritance • Characteristics: mostly males with disease, passed to sons by mother, father cannot pass the gene • Sex influenced traits: affected by presence of testosterone, estrogen

  9. Genes and Behavior • Mechanism • Product from gene-specific proteins • Proteins have specific functions leading to phenotypes • Protein Functions: hormones, enzymes, structural, neurotransmitters

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