Chapter 9 - Genetic Diversity and Adaptation

Occur - formation of gametes

Change in Nucleotide basis

Subsitution- nucleotide replaced = possible change of amino acid (change bonds = shape (tertiary) = function.

Can have no affect (DNA degenerate code)

Deletion - nucleotide lost = amino acid sequence will change (DNA triplet code) = won't function properly

Chromosome Mutation - change in structure of whole chromosome (sponataneoulsy)

Change in whole set = polyploidy 3+ sets of chromosomes (normal = 2)

Change in number of individual chromosomes - fail of homogolous pairs to seperate ( upon fertilisation all body cells will have more or less chrosomes than normall in all their body cells- meiosis = non-disjunction e.g Down's syndrome.

Process for an Organism With 1 Chromosome

First Division (meiosis 1) 

• Homologous chromosomes pair up - causes variation indepentdent assortment
• Chromatids wrap around each other
• Crossing over occurs
• Homologous pair seperate
• One chromosome in one of two daughter cells

Second Division (meiosis 2)

• Chromatids move apart
• Four daughter cells formed

Gene - length of DNA that codes for a polypeptide.

Locus - position of the gene on a chromosome or DNA molecule.

Allele - one of the different forms of a particular gene.

Homologous Chromosomes - pair of chromosomes - one maternal one paternal (have same gene loci)

Number of possible combinations of chromosomes for each daugher cell:

2  where n = number of pairs of homologous chromosomes

Number of possible combinations of chromosomes from male and female gametes:

(2  )  where n = number of pairs of homologous chromosomes

All members same species have same genes - characteristic expressed = alleles

Genetic Diversity - the total number of differenct alleles in a population.

• The more alleles all indivduals = higher genetic diversity
• More able to survive environmental change - wider range alleles = wider range characteristics
• Greater possibility that some individuals will survive environmental change

Gentic diversity enables natural selection.

Reproductive success affect allele frequency in a population.

Process:

• In a population of a species gene pool -wide variety
• Random mutations will occur = possible new allele - possibly advantageous
• Individual with benefial allele = successful - competing for resources (live longer)
• Increases chance breeding/producing offspring
• Benefital allele passed onto next generation
• Offspring more likely to thrive/reproduce
• Over many generations the number of individual with benefical allele increases at the expense of those with less benefital allele of that paricular characteristic.

Directional Selection

Favours organisms extremes of the mean.

Occurs - change in the environment.

Example: Antibiotic Resistance:

• Spontaneous mutation
• Bacteria produces enzyme - break down peniciliin
• By chance bacterium in environment with penicillin
• = mutation benefical = survived while other bacterium died
• Bacterium survived = reproduced (binary fission)  = small pop. resistant bacteria
• Pop of resistant bacteria increased at expense of non-resistant bacteria = populations normal distribution curve shifts to the direction of a population with greater resistance

Stabilising Selection

Favours indivual woth phenotype closest to the mean = more likely to pass on alleles