1. 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.

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. 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

10. 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

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

12. 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