Topics 4 and 10 GENETICS

1. Topics 4 and 10GENETICS Genetics is the study of how inherited information is passed on from one generation to the next using genetic material….genes made of DNA.

2. Topic 4.1 Eukaryotic Chromosomes • Made of DNA wrapped around histone proteins • In eukaryotes that reproduce sexually chromosomes always come in pairs (except in sex cells or gametes) • Humans have 46 chromosomes (or 23 pairs) • Prokaryotes (bacteria) have only one chromosome and it is not associated with proteins

3. Chromosomes in different species

4. Topic 4.1.2Define gene, allele and genome • Gene = a heritable factor that controls a specific characteristic • Heritable means passed on from parents to offspring • Characteristic refers to genetic traits such as hair color • Our approx. 30000 genes are organized into chromosomes • Allele = different variations of a gene • ex. Some alleles give you brown eyes and others give you blue eyes • Alleles of the same gene occupy the same place (locus) on each chromosome of a pair

5. Genome = the complete set of an organisms base sequences • Complete genomes have been fully written out for a few organisms (ex. fruit fly and E. coli bacterium) • If each DNA nucleotide base pair (A-T, C-G) were typed out, a human cell would contain more letters than 10 sets of encyclopedias!!!!!

6. Topic 4.1.3 Define Gene Mutation • A mutation is a random, rare change in genetic material • A gene mutation involves a change of the sequence of bases in DNA • e.x. the base thymine (T) might be put in place of adenine (A) along the DNA sequence • This results in the corresponding bases along mRNA being altered during transcription • This could lead to errors in translation and protein synthesis

7. Topic 4.1.4Explain base substitution mutation using the example of sickle cell anemia • Consequence of changing one base could mean that a different amino acid is placed in the polypeptide chain • This may have little or no effect on the organism or it may have a major influence on the organism’s characteristics • In humans, a mutation is sometimes found in the gene which creates hemoglobin for red blood cells. • The resulting condition is called sickle cell anemia

8. Sickle Cell Anemia • Caused by a base substitution mutation • Codon GAG becomes GTG so during translation instead of adding glutamic acid, valine is added instead • This causes a change in the shape of the hemoglobin molecule which leads to a very different shape to the red blood cell • Sickle is a curved knife used to cut tall plants • O2 cannot be carried efficiently leading to weakness, fatigue and shortness of breath • The hemoglobin tends to crystallize within the red blood cells leading to slow blood flow or blockages

9. Demographics of sickle cell = the mutated gene is found mostly in populations originating from West Africa or the Mediterranean • Sickle cell disease and malaria • Malaria is one of the most deadly diseases in the world • The parasite which causes malaria has difficulty infecting a person with sickle cell • People with sickle cell have a natural resistance to malaria • Therefore the mutated gene has been successfully passed on through natural selection

10. Exercises: • Draw and label a chromosome. Include the following labels: chromatid, centromere, Indicate an example of a locus. • What is the difference between an allele an a gene? • Compare and contrast prokaryotic DNA and eukaryotic DNA. • Explain why eukaryotic chromosomes always come in pairs.