CHAPTER 19 GENETICS AND INHERITANCE PowerPoint® Lecture Slide Presentation by Robert J. Sullivan, Marist College Human Biology Concepts and Current Issues Second Edition MICHAEL D. JOHNSON CHAPTER 19 GENETICS AND INHERITANCE Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

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

Punnett Squares Figure 19.2

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

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

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

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

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

Chromosomes May be Altered in Number and Structure Nondisjunction during meiosis Examples: Down syndrome: trisomy 21 Alterations of the number of sex chromosomes XYY: double-Y syndrome XXY: Klinefelter syndrome XXX: trisomy-X syndrome XO: Turner syndrome, no Y Deletions and Translocations: alter chromosome structure

Inherited Genetic Disorders Mechanism Most mutations usually involve recessive alleles Phenylketonurid Tay-Sachs Disease Dominant lethal allele: Huntington Disease Always expressed, though at midlife Always lethal

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

Modifying DNA Recombinant DNA technology: cutting, splicing and copying DNA, polymerase chain reaction (PCR) Genetic engineering Microorganisms: factories for human proteins, vaccines, environmental applications New plants for agriculture New uses for domestic animals Human gene therapy