CHAPTER 1 Genetics: An Introduction Authored by Peter J. Russell

Genetics is the study of heredity and variation  It is the unifying discipline in biology The central theme in genetics is the gene  A gene is defined as a unit of heredity  Genes provide the blueprint that determines the traits of an organism Geneticists and Genetic Research

Four Subdisciplines of Genetics Transmission (or Classical) genetics deals with the movement of genes and traits from parents to offspring, and with genetic recombination Gregor Mendel is considered the father of genetics  He concluded that each organism contains two copies of each gene, one from each parent, and that alternative versions of the genes (alleles) exist  Ultimately, the terms Homozygous, Heterozygous, Phenotype, Genotype were coined Sources of Genetic Variation include…  Mutation: changes in the genetic material (sequence)  Recombination: exchange of genetic material between chromosomes (imparting a novel sequence) [Bcl]  Selection: favoring certain combinations of genes over others

Molecular genetics deals with the molecular structure and function of genes, the expression of genes within the genome and genomic analysis

Population genetics studies heredity in populations of genes that are determined by one or just a few genes  Studies in the field measure changes in allele frequency within and over time (evolutionary genetics)  These endeavors are termed the Hardy-Weinberg evaluation of allelic frequency in populations Quantitative genetics studies group heredity for traits determined by many genes simultaneously  In other words, these are multifactorial traits which are influenced polygenically  The environment also plays a role in the expression of particular traits (anybody in the audience ever have a suntan?)

Genetic Databases and Maps Information is available at the national Center for Biotechnology Information (NCBI)  PubMed: access literature citation & abstracts  OMIM (Online Mendelian Inheritance in Man): database of human genes & genetic disorders  Genbank: the NIH genetic-sequence database. Can search by entering the name of a specific genetic disease  BLAST (Basic Local Alignment Search Tool): compare new sequence with known to find match with known sequences  And many, many more!

Genetic Map The locus is the position of a gene on a chromosome  Local distance is calculated by the recombination frequency  Map unit (or Morgan): is the unit of genetic distance

Organisms for genetic research Desirable qualities for an experimental organism include:  A well-known genetic history.  A short life cycle so that generations can be studied in a relatively short time.  A large number of offspring from each mating.  Ease of growing and handling the organism.  Marked genetic variation within the population.

A cutaway diagram of a generalized prokaryotic cell  Smaller in size  Single celled  Possess a Cell wall over a Cell Membrane  Have a lipopolysaccharide capsule for protection  Have pili and flagella for locomotion  DNA is in a nucleoid region of the cell and is in single copy  Have extrachromosomal DNA called plasmids  LACK ORGANELLES

Eukaryotic cells Generally larger in size Can be a single cell (yeast) or multicellular (us) Have membrane enclosed nucleus containing DNA and have membrane bound organelles possessing specialized functions i.e. fungi, plants or animals

Cutaway diagrams of generalized Eukaryotic cells

Plant cell vs Animal cell (summary) Similarities:  Have a plasma membrane enclosing the cytoplasm  Have a nucleus containing chromosomes which are surrounded by a membrane with nuclear pores  Organelles: endoplasmic reticulum, ribosomes, mitochondria, golgi bodies Differences:  Plant cells have a cell wall, chloroplasts and a central vacuole. Animal cells lack these structures.  Animal cells have centrioles, which are involved in cell division (plants roll a different way…)