Honors Biology Unit 6 • “Back to Mitosis” • Gregor Mendel never observed chromosomes, genes, mitosis or meiosis. His work identified “factors” of heredity but these “factors” remained a mystery until improvements in microscopy allowed scientists to observe the details of cell division. • The scientist who first observed chromosomes during mitosis in 1882 was Walther Flemming.
The chromosome theory states that hereditary factors, or genes, are carried on chromosomes (Walter S. Sutton, 1903). Walther Flemming
How did this theory come to be? • Observations… Chromosomes in grasshoppers line up in pairs during meiosis. Pairs are “homologous”… similar in shape and size just like Mendel’s “factors”. Chromosomes behave according to Mendel’s principles. • Supporting Evidence • 1. 1st the egg and sperm were known to be the only physical link between generations. • 2. 2nd Males and females appeared to contribute traits to offspring equally. • 3. 3rd Nuclei in egg and sperm about the same size even though the egg is larger and has much more cytoplasm • So… heredity factors must be in the “nucleus”
Genes and chromosomes: Organisms have more traits than chromosomes – each chromosome therefore must carry hundreds of genes. • Example: Sutton was observing Grasshoppers, 12 pairs of chromosomes producing hundreds of traits. • The Sex Chromosomes (X,Y)
Classic experiments with Drosophila or fruit flies (10-15 day life span) by Thomas Hunt Morgan Demonstrating that a specific gene (such as eye color) is located on a chromosome.
Why is Drosophila a good choice for the study of heredity? • 1. easy to keep and breed • 2. small, 100’s in a small vial • 3. life span 10-15 days • 4. many generations in short time • 5. only 4 pairs of chromosomes
X Chromosome (rod shaped) and Y chromosome (hooked shaped) • Each egg has X • Each sperm has X or Y • The chromosomes that determine the sex of an individual are called the sex chromosomes. The other chromosomes are called the autosomes .
Fertilization and sex chromosomes – (draw) • Sex Linkage in Fruit Flies • The White eye experiment • Two types of eyes – red or white. • Thomas Morgan crossed a red eyes female with a white eyes male. All of the white eyes disappeared. Then he crossed the babies (both male and female with red eyes). • He got ¾ red and ¼ white. BUT all of the white eyed babies were male. How do you explain this? Explain Using Punnet Squares
Fruit Flies Mating • Morgan’s experiments confirmed Suttons’s hypothesis that genes are found on chromosomes. Since males have only one chromosome – any allele present will be expressed. How can the recessive alleles be expressed in females?
Human Traits which are sex linked include: • 1. Red Green Color Blindness • 2. Hemophilia • 3. Duchenne Muscular dystrophy • Which sex is more likely to exhibit a sex linked trait? • Male
Karyotypes • A picture of the chromosomes in a cell from an organism is called a • Karyotype • 1. Tissues used for chromosomes analysis • a. Blood Cells/Lymph Cells • b. Amniotic Fluid (surrounds fetus) • c. Skin • d. Bone Marrow
KARYOTYPING RULES • A. Chromosomes are arranged according to size from largest to smallest with the short arm (p arm) up and the long arm (q arm) down. • B. Each chromosome is paired up with its matching homolog so there are two chromosomes in each space. Each homolog has the same banding pattern and centromere index. Unless there is an abnormality, the banding and centromere index are always the same for each numbered pair.
a. Metacentric centromeres (# 1 and 3) • b. Telocentric centromeres (#13 and 21) • c. Sub-metacentric centromeres (#2 and 6) • Sex chromosomes are put into the X or Y spaces • The Karyotype is Named with number first and then the sex chromosomes, and then the abnormalities present.
THE CHEMISTRY OF GENETICS • When analyzed by biochemists, chromosomes were found to be made up of two different chemicals which were: • 1. DNA • 2. Proteins • For years scientists thought that protein was the genetic material but in 1950 it was discovered that DNA was that material:
The Puzzle and the Proof • Two strains of Streptococcus – Strain S had a protective capsule and will kill mice by giving them pneumonia. Strain R is harmless and has no capsule. • Experiment • 1. Kill the deadly strain S with heat • 2. Inject into mice – no pneumonia • 3. Inject mice with heat killed S and living R – pneumonia and death
Why? • Did Strain S come back from the dead? How did they solve this? • They realized that the virulent strain could transfer the DNA to the non-virulent strain and make it deadly
James Watson Francis Crick • MOST IMPORTANT OF ALL SCIENTIFIC DISCOVERIES • Discovering the structure of DNA by ______________ and _____________ • Chemical make-up of DNA. It consists of four nitrogenous bases: • 1. Adenine • 2. Guanine • 3. Cytosine • 4. Thymine • DNA also has two other molecules: • Ribose Sugar • Phosphate Backbone
A unit made of a nitrogen-carrying base, a sugar molecule and a phosphate group is called a Nucleotide • The Watson-Crick Model • Known information about DNA: • 1. The amount of guanine always equals the amount of cytosine • 2. The amount of adenine always equals the amount of thymine • Images of DNA were made by a biophysicist named • Rosalind Franklin
James Watson • The DNA image looked like what? • A Ladder • Two graduate students named ________________ and _________________ worked in a laboratory with tinker toys and figured out the structure. They published first. • Determined that DNA is shaped like a • Spiral Ladder or Spiral Staircase. • The sides of the ladder (helix) consists of alternating Phosphates and Deoxyribose Sugars. • The rungs of the ladder consist of • Nitrogenous Bases (Adenine, Guanine Cytosine, Thymine) Francis Crick
The sequence of the nucleotides is the code that controls the production of all the proteins in an organism. • A gene is a sequence of nucleotides that controls the production of a polypeptide or an RNA molecule. • Scientists estimate that the information stored in one cell is the amount in 500-1000 page books.
Replication of DNA • Cells make copies of their DNA in about six hours through a process called: • Replication • To make a copy: • 1. DNA unwinds with help from enzymes • 2. Enzymes pair complimentary nucleotides on each side. • 3. Other enzymes link other nucleotides into 1 long strand. • Each original strand serves as a template (blueprint) or pattern. • Each completed DNA molecule contains one old and one new strand. • The enzyme responsible for this is • DNA Polymerase
DNA AND PROTEIN SYNTHESIS • DNA controls protein synthesis • DNA is located in the • Cell Nucleus. • Protein synthesis takes place in the • Cytoplasm of the cell • DNA molecules do not leave but use a messenger called • RNA or Ribonucleic Acids. • DNA and RNA are similar in many ways but have 3 key differences: • 1. Contains the sugar Ribose instead of Deoxyribose • 2. Uracil is substituted for Thymine in RNA • 3. RNA is single stranded where DNA is double stranded
There are three kinds of RNA • 1. Messenger RNA (mRNA) (carries sequences from nucleus to ribosome) • 2. Transfer RNA (tRNA) (picks up amino acids and carries them to ribosome. • 3. Ribosomal RNA (rRNA) (binds mRNA and tRNA together)
TRANSCRIPTION • Process by which mRNA is copied from DNA is called • Transcription • What happens? • 1. 1 strand of DNA separates from helix (template) • 2. mRNA binds to the DNA making a sequence for proteins
The SECRET CODE • We need a code made of DNA to make a protein. • There are 20 amino acids. • If a code = 3 bases (AUG) – How many amino acids? • 1 Amino Acid • Experiments have confirmed the triplet codon. Each set of 3 letters = one Amino Acid.
Codons code for all amino acids (redundant). • They also code for STOP, START, and other punctuation. • AUG = Start and/or UGA, UAA, UAG=Stop.
Lets try a simple mRNA code Transcription: • AUG-UAC-UUU-GUU-GGA-AAA-UCU-UGA
TRANSLATION • After transcription, the mRNA moves out through a • Nuclear Pore • In the cytoplasm mRNA and, rRNA, tRNAcomplete a process called Translation. • Several ribosomes are used (at the same time sometimes). • Ribosomes: 2 part segment that is the workbench for building proteins
Made up of 2 Separate parts (includes rRNA) • Also needed is Transfer RNA (tRNA)- which picks up a specific amino acid and carries it to the mRNA and ribosome complex. • Translation • The cytoplasm has more than 20 kinds of tRNA – • at least one for each amino acid • tRNA (80 nucleotides long)
The sequence of three bases which matches mRNA is called the Codon. UAA, UUU, AAU, AUG • Once the tRNA has bound to mRNA an enzyme in the ribosome links the new amino acid by means of a Peptide Bond. • There is no tRNA for the termination codon so the chain is released and the protein is completed. (It may go to the golgi body now for modifications).
Transformation Lab – pGlo • Focus Questions pg 39 • 1. To genetically transform an entire organism, you must insert the new gene into every cell in the organism. Which organism is better suited for total genetic transformation – one composed of many cells, or one composed of a single cell? • Singled Cell Organisms. • Multi-celled organisms often have cells with different jobs, and the genes would be expressed differently • 2. Safety is another important consideration in choosing an experimental organism. What traits or characteristics should the organism have (or not have) to be sure it will not harm you or the environment? • It should not be pathogenic (harmful to a human body, or a germ) • It should be able to multiply quickly to observe large quantities at a time. • The cells should be expressing the same DNA • 3. Based on the above considerations, which would be the best choice for a a genetic transformation: a bacterium, earthworm, fish or mouse? Why? • Bacterium: they divide quickly, can be contained in a small area, and the cells each express the same genetic information
DATA Collection: pg 40 • Carefully observe and draw what you see on each of the four plates. Put your drawing in the data table below. Record your data to allow you to compare observations of the +pGLO cells with your observations for the non-transformed E. Coli. Write down the following observations for each plate. • a. How much bacterial growth do you see on each plate, relatively speaking. • b. What color are the bacteria • c. How many bacterial colonies are on each plate (count the spots)
ANALYSIS pg 41 • 1. From your results, can you tell if these bacteria are ampicillin resistant by looking at them on the LB plate? • Yes, if Bacteria grow on the plates that contain Ampicillin, then the bacteria have developed a resistance. • 2. How would you change the bacteria’s environment to best tell if they are ampicillin resistant? • Once the bacteria have grown on the plate, ampicillin would be place directly on the bacteria. If they continued to grow, then they would be resistant to bacteria
3. Very often an organism’s traits are caused by a combination of its genes and its environment. Think about the green color you saw in the genetically transformed bacteria. • a. What two factors must be present in the bacteria’s environment for you to see the green color? • There must be the enzyme necessary for gene transformation (beta-lactamase) pGLO and arabinose sugar in the agar. • b. What do you think each of the two environmental factors you listed above are doing to cause the genetically transformed bacteria to turn green. • The gene that provides resistance to ampicillin also contains the jellyfish gene • The gene is also turned on to break down arabinose for food for the bacteria • c. What advantage would there be for an organism to be able to turn on or off particular genes in response to certain conditions? • This allows the bacteria to be able to adapt to more conditions (allows it to survive in less than ideal situations)
4. How might transformation be used: • a. In agriculture? • Growing better crops. Genetically Resistance to disasters • Bacteria Killing insects • Nitrogen fixing bacteria • b. In medicine • Make hormones like insulin that are in high demand • Penicillin • Cancer treatment • c. In environmental disasters???? • Use bacteria to re-cultivate the natural plants and soil in the area
CHANGES IN THE GENETIC CODE • DNA usually copies itself exactly • Occasionally, replication makes mistakes or environmental factors cause a change in the genetic code. • This change is called a Mutation. • The product of this change is the • Genetic Disease
Diseases that are caused by these gene mutations happen often. Some diseases are: • 1.Down’s Syndrome • 2. Muscular Dystrophy • 3. Turner’s Syndrome
Mutations that cause the death of the offspring are called Lethals. • Chromosome mutations • Involve changes in many genes. • Deletion, Inversions and Translocations • Somatic and Germ Mutations • Germ mutations occur in Sex Cells (transmitted to offspring) • Somatic mutations occur in Body Cells (only individual is affected)