Topic 3

• Define gene.


  A heritable factor that consists of a length of DNA (not an entire chromosome) and influences a specific characteristic
• Define allele.


  Various forms of a gene
• Define locus.


  The position a gene occupies on one type of chromosome
• Define genome.


  The whole genetic information of an organism
• How do alleles differ from one another?


  By a few differences in DNA base sequence
• What is the genome size (million base pairs) of the following have?1) T2 phage virus2) E Coli3) Fruit fly 4) Human5) Woodland plant


  1) 0.182) 53) 1404) 3,0005) 150,000
• 1) How was John Cairns contributed to science?2) How did he manage to do this?


  1) Tried to determine number and direction of replication, found accurate length of chromosomes during supercoiling in mitosis2) Autoradiography (label chromosome by growing cultures in medium containing thymidine) + Isolation (of chromosomes by lysing cells and placing under electron micrograph)
• Define homologous chromosomes.


  Pair (one from each parent) of chromosomes that have same size, band sequence, shape and genes; may have different alleles
• 1) Define crossing over.2) Define chiasma.


  1) Exchange of alleles between non-sister homologous chromosomes in prophase I2) Where the two alleles of both homologous chromosomes connect

  
• Define independent assortment.


  Sorting of chromosomes during making of gametes in metaphase I
• Define Meiosis.


  The reduction division of diploid cells (2 sets of chromosomes) resulting in 4 haploid cells (1 set of chromosomes)
• Amniocentesis.


  A hypodermic needle is inserted through the abdomen to extract sample amniotic fluid from the amniotic sac, during the 14th-16th week of pregnancy
• Scientists use three key features to identify chromosomes. What are they?


  Banding pattern, centromere position, size
• What are karyograms? How are they organized?


  Karyograms are pictures of chromosomes arranged in homologous pairs by size (largest to smallest) with sex chromosomes last.
• Define genotype.


  Alleles possessed by an organism

  
• Define phenotype.

  Physical characteristics of an organism

  
• Define dominant allele.


  Same effect on phenotype whether in homozygous or heterozygous state, masks effects of recessive alleles
• Define recessive allele.


  Only has effect on phenotype when present in homozygous state
• Define codominant alleles.


  Pairs of alleles that have a joint effect on the phenotype when present in heterozygote
• Define homozygous.


  Having 2 identical alleles of a gene (left image)

  
• Define heterozygous.


  Having 2 different alleles of a gene (right image)

  
• Define carrier.


  An individual with one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for the allele
• Define test cross.


  Testing a suspected heterozygote by crossing with a known homozygous recessiveWe know the genotype of an individual with a recessive phenotype. Crossing this with an individual with the dominant phenotype will help determine its genotype. If any offspring express the recessive trait, both parents must have recessive trait.

  
• Gregor Mendel's experiment.


  Crossed pea plants until pure breeds (parental generation) > crossed those to get all heterozygous plants for each trait (F1 generation) > crossing those (F2 generation) resulted in ratio predicted on punnett squares
• 1) Define zygote.2) A zygote has (#) alleles of each gene. They or may not be the same (this).


  1) Diploid cell that is the result of fusing gametes2) Two alleles, allele
• Sex linkage:


  A gene located on X chromosome
• 1) What is an autosomal dominant genetic disease? An autosomal recessive? 2) Most genetic diseases are rare because they are (these) alleles.


  1) Huntington's Disease; Cystic Fibrosis2) Recessive alleles
• Define recombinant rDNA and outline how it is made.


  The combination of DNA from other species; Plasmid is removed from the bacterium > restriction endonuclease cuts open a section of DNA from the plasmid > restriction endonuclease cuts out a section from the DNA of another organism > this DNA can then be added to the plasmid and spliced together by DNA Ligase > rDNA can be inserted into host organism and cloned for gene's effect

  
• Bt and Monarch Butterflies:1) The Bt gene has been transferred into (this) to produce (this to do this) but has also affected insects.2) Bt toxin produced in all parts including (this). How?


  1) Corn, produce a toxin to kill pest/insects that eat the corn2) Pollen; monarch butterfly larvae feed on milkweed that sometimes grows close to corn crops -> wind blows pollen from corn onto milkweed leaves that can poison larvae
• What are health benefits and risks of GM crops?


  Benefits- Increased nutritional value- Natural allergens and toxins can be removed- Possibility of putting vaccines in cropsRisks- Protein inserted could cause allergic reaction or toxic- Antibiotic resistance genes used as markers could spread to bacteria and would be resistant- Mutation of genes could cause unexpected problems
• What are environmental benefits and risks of GM crops?


  Benefits- Less insecticide used if a gene to make the toxin can be transferred to the plants- Less fuel used by machinery due to reduced need for plowing and spraying- Improved shelf life of fruit and vegetablesRisks- Non-target organisms could be affected- Herbicide resistant plants could spread pollen to other crops making them also resistant- Decreased biodiversity
• What are agricultural benefits and risks of GM crops?


  Benefits- Can be made to be resistant to drought or salt- Non-herbicide resistant crops can be sprayed and eliminated so there is less competition- Produced to be resistant to plant diseases caused by virusesRisks- Crop spreads too much and unwanted crops cannot be controlled by herbicides- Pests can evolve resistance to pesticide including non-targeted pests that were scarce, but now thrive- Farmers cannot save and re-sow seeds from crops grown so strains adapted to local conditions cannot be developed, seeds engineered each generation
• Define clone. Describe the process of cloning.


  Group of genetically identical organisms or cells derived from single parent cell; Egg is taken from the donor and the nucleus is removed > mitchondrial DNA is taken from the organism to be cloned > this is fused with the egg using electricity > the new cell is implanted into the female organism