Genetics Lecture 14, 10/1: Extranuclear inheritance, Sexual determination in Drosophila

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• TEST 2 MATERIAL
  
• • We are responsible for epistasis problems for the test (started it before exam 1)
• • Sex-linked traits
• • Nature vs. nurture. Multiple choice, short answer, essay
• • 3 to 4 problems comprising 50% of the credit. Mult. Choice is 20% and short ans. 30%.
• • Up through organelle heredity
• • Review is at NOON
• • Sex determination in Drosophila (unique system where they are more than male or female) (6:25)
• o 1916 Calvin Bridges
• • looking for the sex determination in fruit flies. He found that the mechanism was not Y dependent. He found that it was the ratio of X chromosome to autosomes determined the sex of the fly.
• o normal diploid female has 2 autosomes for every 2 x chromosomes. Ratio of 1.0
• o Triploid female extra copy of autosome and x chromosomes: total 3 autosomes to 3x chromosomes - ratio of 1.0
  

• o any arrangement with 1.0 would be a female
• o 3 x chromosomes for 2 autosomes gives ratio of 1.5. These are called metafemales: weak, infertile, low viability
• o Males have ratio of 0.5 two cases.
  
• • one x chromosome to two autosomes. Lack the Y chromosome leaving them sterile
• • One x chromosome one y chromosom --> fertile. Y chromosome determinse fertility, not maleness.
• o Metamales (14:20)
• • Ratio of 0.33. 1 x chromosome fore every 3 autosomes. They are weak and infertile
  
• o 2 classes of flies with ratios between 1 and .5 - Intersex flies
  
• • Intersex flies come about when there is: 3 X Chromosomes to 4 autosomes or 2 X chromosomes to 3 autosomes
• • Intersex flies: rudimentary gonads, sterile morphological, display both male and female (end of chap 7)
• • Chapter 9 (17:45) Extranuclear inheritance: anytime inheritance is not base on the DNA in the cells nucleus.
• o Ex. Organelle heredity – have DNA in the chloroplast and the mitochondria which influence phenotype. Always mother to offspring – egg contributes all of the cytoplasm → Organelles are in the cytoplasm.
• o Ex. Infectios Heredity – phenotype associated with a microorganism living in a cell.
• o Ex. Maternal effect – proteins in the egg which determine a particular phenotype in the offspring.
• o Only organelle heredity is DNA based
• • ORGANELLE HEREDITY (24:00)
• o 1908 Carl Correns worked with four O’clock plants. Either have white leaves, green, or veriegated leaves.
• o If the progeny came from a fertilization of an ovum from a plant with green leaves then the progeny had all green leaves.
• o Phenotype of the offspring was always the same as the phenotype of the parental plant that gave the ovum.
• o Phenotype is associated with the DNA of the chloroplast.
• Mitochondria can show the same pattern (28:10)
• o 1952 Mary and Hershey Mitchell studying Neurospora (bread mold) cross. Discovered a strain that they named Poky Strain (it grew slowly). Determined that the phenotype was associated with a mutation in the mitochondrial DNA. The mitochondria generates energy through respiration. Thus a mutation in the mitochondria would result in the slow growth phenotype.
• o Female poky x male WT THEN all progeny are were poky
• o female WT x male poky THEN all progeny were WT
• o The question: Do chloroplasts and mitochondira have their own DNA? → Yes
• o Cytoplasmic inheritance occurs through the cytoplasm of the egg. The sperm contributes NO cytoplasm.
• (35:30) DNA of the chloroplast
• o Uniform in size and shape and ranges from 100kB to 225kB (kb=kilobases)
• o Circular double stranded DNA with no associated proteins.
• o Genes found in chloroplasts DNA – genes for rRNA, tRNA ribosomal proteins and RNAPOL. This allows them to do their own transcription and translation independent o the cells individiual mechanisms for transcription and translation. They also have genes for photosynthesis.
• (38:40) Mitochondrial DNA
• o 16kB to 36kB
• o rRNA’s 22 different tRNA’s
• o genes whose products play a role in oxidative phosphorilation.
• o Ribosomes of mitochondria are quite different than the ribosomes of the rest of the cell.
• • Mitochondrial mutations associated with human diseases (41:30)
• o DNA in the mitochondria is particularly likely to be mutated
• o How do we determine that a human disease is mitochondrial in nature?
• • Inheritance pattern should be maternal and not mendelian.
• • Deficiency must result based on loss of energy for the cell
• • You must have a mutation in the gene in the mitochondrial DNA associated with the disease.
• o Myoclonic epilepsy and ragged red fiber disease (45:25): lack of coordination, deafness, dementia, epileptic seizures mutation in the mitochondrial gene for tRNA
• o Lebers hereditary Optic Neuropathy: Sudden bilateral blindness, avg. onset of 27
• o Kearns Sayre Syndrome: Hearing loss, loss of vision and heart condition. Normal childhood with an onset in early adulthood.

This will be material for TEST 3 ----------

• • INFECTIOS HEREDITY (50:25)
  
• o Eukaryote living in a symbiotic relationship with a microorganisms and leads to a phenotype.
• o EX. Paramecium Aurelia → a toxic substance which kills sensitive cells. Maintained by the Kappa gene.
• o Dominant K (kappa particle) allele to have the killer phenotype. You also need the microorganism which requires cytoplasmic exchange during paramecium mating.
• o Conjugation with cytoplasmic exchange or without.