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

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

Chromosomes in different species # of chromosomes Fruit fly 8 Human 46 Rye 14 Ape 48 Guinea Pig 16 Sheep 54 Dove Horse 64 edible snail 24 Chicken 78 Earthworm 32 Carp 104 Pig 40 Butterflies ~380 Wheat 42 Fern ~1200

Topic 4.1.2 Define 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

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!!!!!

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

Topic 4.1.4 Explain 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

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

Sickle cell disease and malaria 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

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.