Historically Significant Work of Prominent Geneticists

 

Gregor Mendel – Father of modern genetics – Austrian monk, worked with pea plants in

                            the mid-1800s. Laid the foundation for genetics with the principles of

                           dominance, segregation, and independent assortment.

 

Walter Sutton – developed the Chromosome Theory of Heredity – the theory that states

                          that genes are located on chromosomes and that each gene occupies a

                          specific place on a chromosome.  That specific location is called the

                          locus. Sutton developed his theory in the early 1900s.

 

Thomas Hunt Morgan – studied the fruit fly, Drosophila melanogaster, discovered

                                       linkage or linked genes.  Linked genes do not undergo

                                       independent assortment.  They are inherited together because

                                       they are close together on the same chromosome.  They are not

                                       separated by crossing-over. He also worked with sex-linked traits

                                       in Drosophila.

 

Nettie Stevens – early 1900s discovered sex chromosomes.  She studied meal worms,

                           the larval stage of the Tenebrio beetle. Her discovery of the Y

                           chromosome made possible a correct explanation of sex-linked

                           inheritance.

 

Alfred Sturtevant – used crossing-over and linkage to determine the locus of certain

                                genes.  This led to gene mapping. Which has led to the Human

                               Genome Project.

 

Josef  Kolreuter – 1760, German scientist who discovered incomplete dominance.

 

Francois Jacod and Jacques Monod – 1961, developed the operon model of gene

                                                             expression in prokaryotes.

 

Philip Sharp and Susan Berget – 1976, discovered the introns and exons of eukaryotic

                                                     gene expression.  Introns are segments of DNA that do

                                                     not code for a protein and must be removed from

                                                     mRNA before it leaves the nucleus.  Exons are the

                                                     segments that code for the protein.

 

Barabara McClintock – discovered “jumping genes”. In the 1940s and 1950s McClintock's

                                         work on the cytogenetics of maize led her to theorize that genes are

                                         transposable -- they can move around -- on and between

                                         chromosomes. McClintock drew this inference by observing changing

                                         patterns of coloration in maize kernels over generations of controlled

                                         crosses. The idea that genes could move did not seem to fit with what

                                         was then known about genes, but improved molecular techniques of the

                                         late 1970s and early 1980s allowed other scientists to confirm her

                                         discovery, and consequently she was awarded the Nobel Prize in

                                         Physiology or Medicine in 1983.

 

 

Evalulate Karyotypes for Abnormalities

 

Karyotype – all of the chromosomes in a cell or an individual organism, visible

                     through a microscope during cell division  The following is a normal

                     karyotype.

 

 

Monosomy – the absence of one chromosome of a homologous pair in the complement

                     of an otherwise diploid cell, as seen in Turner’s syndrome and various

                     other conditions.

 

Turner’s syndrome – phenotypically female, characterized by short stature, variable

                                  abnormalities that may include webbing of the neck, and cardiac

                                  defects.  It is associated with the absence of the second sex

                                  chromosome (XO).

 

Trisomy – the presence of an extra chromosome of one type in an otherwise diploid cell,

                 as seen in Down syndrome or Trisomy 21, and Klinefelter’s syndrome

 

Down Syndrome – a chromosome disorder characterized by a small, flattened skull,

                               short, flat-bridge nose, and moderate to severe mental retardation.

                               The chromosomal aberration is trisomy of chromosome 21

                               associated with late maternal age.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Klinefelter’s syndrome – a syndrome of males with variable degrees of masculinization,

                                        patients tend to be tall, with long legs.  It is associated typically

                                        with an XXY chromosome complement.

 

 

 

 

Compare and Contrast the Different Types of Mutation Events, Including Point Mutation, Frameshift Mutatuon, Deletion, and Inversion

 

Mutation – an alteration in DNA structure or sequence of a gene

 

Chromosomal Mutations

 

• Deletion – chromosome abnormality in which part of the chromosome is missing;

                        loss of one or more base pairs from DNA can result in a frameshift

 

• Duplication – a segment of a chromosome is repeated.  Can result when the piece

                            deleted from a homologous pair attaches to its sister chromosome.

 

• Inversion – a mutation that occurs when a chromosome piece breaks off and

                         reattaches in reverse orientation

 

• Nondisjunction – the failure of homologous chromosomes to separate normally

                                  during meiosis.  The tetrad does not separate properly during

                                 Anaphase I of meiosis.  Nondisjunction results in polyploidy.

                                 Polyploidy is harmful or fatal in animals, but beneficial in plants.

 

Point mutations – a change in a single base pair of a DNA sequence in a gene.

                            An example would be Sickle Cell Anemia. The change in one base

                            pair changes the amino acid code thus changing the protein.  People

                            heterozygous for normal blood but carrying a gene for sickle cell

                            anemia have a natural defense against malaria. People homozygous

                            for sickle cell anemia have a serious illness.

 

Frameshift mutations – a mutation that results in the misreading of the code during

                                      translation because of the change in the reading frame.

                                      Frameshift mutations are caused by the addition or deletion of

                                      a nitrogen base. Thus changing the codons on mRNA and

                                      changing the amino acids coded and changing the proteins.

 

Somatic mutations – occur in the body cells and are not passed on to offspring

 

Germ mutations – occur in the germ cells, the gametes, the sperm and egg, and are

                              passed on to offspring

 

Identify Effects of Changes Brought About by Mutations 

 

     Most mutations are harmful as can be seen by the diseases discussed.  Some mutations can be beneficial such as the heterozygous condition of sickle cell anemia and polyploidy in plants.  Many somatic mutations are neutral with no one even knowing that they have the mutation.  Mutations are one of the driving forces of evolution, producing changes in organisms that may give them either an advantage in their environment or a disadvantage.

 

Relate the Chromosome Theory Of Heredity to Recent Findings in Genetic Research

 

     The chromosome theory has been the basis for the Human Genome Project (HGP).

HGP is a project coordinated by the National Institutes of Health (NIH) and the Department of Energy (DOE) to determine the entire nucleotide sequence of the human chromosomes. The realization that genes determine traits and that they are arranged in a certain order on the chromosomes was the first step in being able to determine the locus of each gene and the trait it controls.

     The chromosome theory is also essential for chromosome therapy, treating diseases by treating the chromosomes.  Huntington’s disease is an autosomal ( non-sex chromosomes) dominant disease characterized by chronic progressive, rapid, complex, jerky, involuntary movements and dementia, onset usually occurs in the forties and death occurs within 15 year. Dr. Nancy Wexler discovered the gene that causes Huntington’s Disease near the end of chromosome 4 in 1983.  Today labs are at work to find ways to treat this deadly disorder.