Continuity Through Heredity

The Dual Role of Genetic Material  Heredity – the transmission of genetic information from one generation to another  The basic unit passed along is the gene  The gene controls the basic function of the cell  Geneticists study heredity and gene action together  The visible effect of gene action in individuals and populations provide clues to the genes that are present in an organism or in a population and how they work

The Dual Role of Genetic Material  Genes  Store information in the sequence of nucleotide bases that make up the DNA or the organism  This molecular code directs all the cell processes involved in the development and function of the organism  Reproduction of the genes – provide continuity between generations  Effects of the genes themselves  Instructions for the structure, function, and development of the organisms during each generation

The work of Gregor Mendel  Central Dogma of Biology  DNA → RNA → Protein  Genes bring about the synthesis of Proteins  Enzymes  Muscle protein  Protein pigment  Instructions stores in a specific sequence of DNA nucleotides (G, A, T, C)  It has taken centuries to unravel this information

The work of Gregor Mendel  Most of our knowledge of genetics has been gained in the last 100 years  Today we have sequenced the human genome  It began in 1860 in a monastery in Austria when a monk named Gregor Mendel set forth the basic principles of heredity  We call this Mendelian genetics

The work of Gregor Mendel  He began an 8 year experiment with garden peas  Contain both male (Stamen) and female (pistil) reproductive parts  They self-pollinate  Mendel isolated the plants so they he could cross- pollinate them  He concentrated on one trait at a time  He used large number of organisms to eliminated as much as possible the results being totally due to chance

The work of Gregor Mendel  He combined the results of many experiments  He used the rules of probability to analyze his results  He then began to recognized distinctive patterns of inheritance

The work of Gregor Mendel  He began with a true-breeding parental generation  Produce offspring that are identical to the parents generation after generation  He worked with 7 different true-breeding traits

Mendel’s first experiment

The work of Gregor Mendel  Laid the groundwork for the understand of dominant and recessive traits  Dominant – the trait that will always appear if the gene for that trait is present  In organisms either homozygous for the dominant gene or heterozygous for that gene  Recessive – the trail the will appear only when the organisms is homozygous for the recessive gene

Gene: The unit of Heredity  Mendel said each pure-breeding plant had two identical copies of a “factor” for that particular trait  He didn’t know what they were or where they were located, but he hypothesized that one copy was found in the sperm and one copy was found in the egg of the parents  The offspring would then receive one copy from each of the parents  Principle of Segregation

Gene: The unit of Heredity  Today we know these “factors” to be genes  The alternative form of the gene is called an allele  The allele for the dominant form is commonly represented by a capital letter and the allele for the recessive form is represented by the same letter in lower case  The alleles form the genetic makeup or genotype  The genotype is responsible for the phenotype – the appearance or observable traits  Two different genotypes can produce the same phenotype. How is that possible?

Genes direct biosynthesis  Changes that are passed on to offspring are called mutations  Beadle and Tatum experiment  Worked with Neurospora crassa spores  Treated with x-ray to induce mutations  New spores wouldn’t grow on simple media  Mutation in the gene that produced that produced an enzyme necessary for the production of an essential amino acid tyrosine  Trait passed on to offspring

Chromosomes and Genes  Theodore Bavaria and W.S. Sutton conclude that genes are located in the nucleus  Further studies with the fruit fly (Drosophila melanogaster) confirmed the chromosomal theory of heredity  Genes are small particles located on the chromosomes

Chromosomes and Genes  Each chromosome contains a continuous sequence of DNA  The DNA is associated with specialized proteins that help regulate gene activity  The location of the gene within the chromosome was less certain and whether it was the protein or DNA that was the genetic material

Chromosomes and Genes  Labeled bacteriophage protein with radioactive sulfur  Labeled the phage DNA with radioactive phosphorous  Results showed DNA was the genetic material

DNA unraveled  The structure was unraveled by Watson and Crick in 1953  Double Helix  Two stands anti-parallel to each other  A sugar, phosphate, and a nitrogen- containing base  4 different bases  Adenine, Thymine, Cytosine, and Guanine

Base Pairing in DNA  A pairs with T  T pairs with A  C pairs with G  G pairs with C  Held together with weak hydrogen bonds

What the model explains  Genes can replicate exactly during cell division  Genes mutate occasionally  Genetic instructions are passed from generation to generation through meiosis and fertilization