GENETICS AND INHERITANCE CHAPTER 19
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. 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 Alleles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. Punnett Squares Figure 19.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. 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 Patterns of Genetic Inheritance
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. 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 Allelic Interactions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. Codominance: both phenotypes equally expressed Polygenic inheritance: multiple genes involved Linked genes: may be inherited together if close on a chromosome Allelic Interactions ( cont.)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. Pedigree Chart: Inheritance Pattern for an X-linked Recessive Disease Figure 19.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. 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 Sex-Linked Inheritance: X and Y Chromosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings. Mechanism Product from gene-specific proteins Proteins have specific functions leading to phenotypes Protein Functions: hormones, enzymes, structural, neurotransmitters Genes and Behavior