GENE DIVERSITY AND ADAPTATION

GENE: length of DNA that codes for a polypeptide

LOCUS: the position of a gene on a chromosome or DNA molecule

ALLELE: one of the different forms of a particular gene

HOMOLOGOUS CHROMOSOMES: a pair of chromosomes, one maternal and one paternal, that have the same genes at the same loci but not necessarily the same alleles

GENE MUTATION

• any change to the quantity or base sequence of DNA 

BASE SUBSTITUTION

• when a nucleotide in DNA is replaced by another nucleotide with a different organic base
• polypeptide may differ by a single amino acid - will have a more pronounced effect if the amino acid is significant
• degenerate nature of the code means the final amino acid sequence may not change at all

BASE DELETION

• when a nucleotide is lost from the DNA sequence
• causes a frame shift in the base sequence
• all base triplets from then on are read differently

CHROMOSOME MUTATION

CHANGES TO WHOLE SETS OF CHROMOSOMES

• occur when organisms have three or more sets of chromosomes rather than two
• known as POLYPLOIDY, occurs mostly in plants

CHANGES TO NUMBER OF INDIVIDUAL CHROMOSOMES

• individual homologus pairs of chromosomes failmto separate in meiosis
• known as NON-DISJUNCTION
• results in gametes have one more or one fwer chromosome
• resultant offspring incorrect number of chromosomes
• e.g. Down's syndrome caused by an additional chromosome 21

MEIOSIS

• cell division producing four daughter cells, each with half the number of chromosomes as the parent cell

WHY IS IT IMPORTANT?

• in sexual reproduction two gametes fuse to give rise to new offspring
• if each gamete had the diploid number of chromosomes, the offpsring would have twice this
• therefore, to maintain the diploid number, each gamete must have the haploid number

HOW DOES IT HAPPEN?

MEIOSIS 1

MEIOSIS 2

HOW DOES…