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.

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

Species # of chromosomes Species # of

chromosomes

Fruit fly 8 Human 46

Rye 14 Ape 48

Guinea Pig 16 Sheep 54

Dove 16 Horse 64

edible snail 24 Chicken 78

Earthworm 32 Carp 104

Pig 40 Butterflies ~380

Wheat 42 Fern ~1200

Chromosomes in different species

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

• 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 4.1.4Explain 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

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

• 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:1. Draw and label a chromosome. Include the

following labels: chromatid, centromere, Indicate an example of a locus.

2. What is the difference between an allele an a gene?

3. Compare and contrast prokaryotic DNA and eukaryotic DNA.

4. Explain why eukaryotic chromosomes always come in pairs.