(9) Genetic Diversity Flashcards
Describe the 3 types of mutations.
1) Nonsense Mutations
Base change results in formation of stop codon.
2) Mis-sense Mutations
Base change results in different amino acid being coded for
Silent Mutation
3) Base change results in formation of same amino acid
Describe Meiosis
Interphase
Cell copies the chromosomes and organelles
Prophase 1:
Chromosomes condense and become visible.
Homologous chromosomes link forming chiasmata
Crossing over takes place
Nuclear membrane breaks down
Centrioles move to opposite poles of cell
Metaphase 1:
Pairs of homologous chromosomes lined up at equator
Anaphase 1:
Spindle fibres shorter
Homologous chromosomes move to opposite poles
Telophase 1:
Chromosomes reached poles
Nuclear membrane reforms
Chromosomes uncoil back into chromatin state.
Cell undergoes cytokinesis dividing into 2 cells (Haploid cells)
Prophase 2:
Chromosomes condense, become visible
Nuclear membrane breaks down
Spindle fibres develop.
Metaphase 2:
Chromosomes lined up on equator of spindle apparatus
Anaphase 2:
Centromere of each chromosome divides
Spindle fibres shorten
Chromatids pulled towards poles of cells
Telophase 2:
Chromatids reach end of poles
Chromatids form into chromatin
Nuclear membrane reforms
Each cell undergoes cytokinesis to produce 2 haploid cells
1 Diploid cell —-> 4 Haploid cells
Each gamete is genetically different
Describe natural selection:
Random mutation of alleles within gene pool may result in a new allele
In some cases new allele is advantageous to the organism.
Hence be more adapted hence more likely to survive, reproduce and pass on alleles to offspring.
Over many generations new advantageous allele causes non advantageous allele to lower
Describe Directional Selection type:
Phenotype on one side of the mean becomes better adapted: more likely to survive + reproduce so more offspring of same phenotype
Increase in allele frequency
Overtime, mean moves to that direction.
One extreme selected while other is selected against
Describe Disruptive Selection type.
Phenotype on both extremes are better adapted.
Both survive + breed
Two extremes selected for different reasons so allele frequency increases. Mean moves. Previous mean selected against. Two extremes selected for.
Describe stabilising selection type
Mean phenotype selected for so better adapted. Mean becomes more selected for.
