1. Chromosomes, genes, alleles and mutations
3.1 Genetics
The Basics
Chromosomes, genes, alleles and mutations

2. Gene:
Allele:
Genome:
a heritable factor that controls a specific characteristic.
one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.
the whole of the genetic information of an organism.

3. Haemophilus influenza
Pathogenic bacterium
How many genes?
1700

4. Oryza sativa
Rice plant
How many genes?
41000

5. 31000 Daphnia pulex Water flea How many genes?
Humans have genes!

6. Locus of a gene The position of a gene on a chromosome
The locus is very specific for each gene and each chromosome.

7. What do these terms mean?
In 1865 Gregor Mendel published his work explaining the characteristics of garden peas.
Genotype
Phenotype
Dominant allele
Recessive allele
Codominant alleles
Locus
Homozygous
Hetrozygous
Carrier
Test cross
What do these terms mean?
He tried to explain how pea plants pass on their characteristics to the next generation. He did this by artificially fertilizing pea plants, selecting parent plants and observing the offspring (studied heritable factors).

8. Alleles represented by letters e.g. Aa, BB, cc Phenotype
Word
Definition
Genotype
Alleles represented by letters e.g. Aa, BB, cc
Phenotype
Characteristic traits of an organism
Dominant allele
Always expressed in the phenotype
Recessive allele
Only has an effect on the phenotype when expressed in a homozygous state
Co-dominant allele
When both alleles affect the phenotype in a hetrozygote
Locus
Gene position on a homologous chromosome
Homozygous
Two identical alleles of a gene
Heterozygous
Two different alleles of a gene
Carrier
When an individual has a recessive allele
Test cross
Test to deduce if an organism carriers a recessive gene
We will study the details of Mendels experiments in chapter 3.4
Remember: a gene is a part of the DNA sequence, so a gene is made of a base sequence. Single alleles, only have small variations in base sequence – variations refered to as SNP’s (snips) Single Nucleotide Polymorphisms.

9.
GenBank
Choose ‘gene’
SEARCH ‘COX1’
Select
Scroll down until you see ‘Nucleotide links’, select ‘FASTA’
You should now be able to see the base sequence for this gene!

10. A mutation is a change in the DNA sequence of a gene
Mutations….
See what happens when the base sequence changes.
A mutation is a change in the DNA sequence of a gene

11. Consequences of base substitution mutation
One base can have large impact, no impact or little impact depending on the protein.
Fruit flies
Extra wings
Eye colour
Number of legs
Shape of wings etc…
Humans
Sickle cell anaemia (GAG become GTG, so glutamic acid is replaced by valine, this affects the final shape of the haemogloblin molecule)
What are the symptoms of sickle cell aneamia?
Which demographics are most at risks of sickle cell?
There is a variety of social issues associated with sickle-cell anemia, including the suffering due to anemia, personal feelings if one has either inherited or passed on the sickle-cell allele, questions relating to the desirability of genetic screening for the sickle-cell allele before having children, and the genetic counselling of carriers of the allele.
There are also ethical issues relating to screening of fetuses and abortion of those found to have a genetic disease.
Usually affects people with African ancestry

12. TOK:
Where a correlation is found, a causal link may or may not be present. The frequency of the sickle-cell allele is correlated with the prevalence of malaria in many parts of the world. In this case, there is a clear causal link. Other cases where there is no causal link could be described as a contrast.
There has clearly been natural selection in favor of the sickle-cell allele in malarial areas, despite it causing severe anemia in the homozygous condition. Natural selection has led to particular frequencies of the sickle-cell and the normal hemoglobin alleles, to balance the twin risks of anemia and malaria.

13. Human Genome Project
Aims?
Timeline?
Results?
International collaboration
Ethical issues