Natural Selection and Genetic Diversity Flashcards
What is a model answer for natural selection?
- Random mutation, new alleles
- New allele is beneficial, increased reproductive success
- Alleles passed to offspring
- Over generations, alleles increase in frequency
What are three types of Natural Selection?
1) Directional Selection
2) Disruptive Selection
3) Stabilising Selection
Describe and explain Directional Selection?
Triggered by a change in environment, desirable allele increases in frequency, passed down generations
(Graph: shift in curve to the right)
Describe and explain Disruptive Selection
Extreme traits favoured over intermediate traits, decrease in intermediate traits.
Graph: curve dips in the middle, peaks at two extremes
Describe and explain stabilising selection
Population stabilises on a particular phenotype, decrease in diversity.
How does deforestation and agriculture reduce biodiversity?
- Habitat reduction
- Food reduction
- Removing plant species
- Prey
- Soil/ Nutrient reduction
What is antibiotic resistance?
Antibiotic- kills bacteria only
Bactericidal- kills
Bacteristatic- stops replication and photosynthesis
Caused by a random mutation etc.
What is Simpson’s Index?
D = N(N-1)/ Sum of n(n-1)
What are different terms for warm-blooded and cold-blooded?
Endotherm and Ectotherm
List the sections in a phylogenetic tree
Domain Kingdom Phylum Class Order Family Genus Species
Define species
A set of organisms that can reproduce to produce fertile offspring
What do the areas in a phylogenetic tree where points branch off represent?
This shows speciation, the beginning of a new species and the extinction of the previous species.
What is the bottle neck effect?
A reduction in allele frequency and variation, followed by a catastrophic event that resulted in a dramatic reduction in the population.
What is the founder effect?
A reduction of allele frequency and variation due to the migration of a small subgroup from the rest of its species.
What are the three types of variation?
- Independent segregation
- Crossing over
- Mutation
Describe independent segregation
When the homologous (same) chromosomes line up randomly in metaphase I
Key thing to remember here is that the chromosomes are lining up randomly. This creates the most variation out of all three.
Describe ‘crossing over’
When homologous chromosomes exchange genetic material with each other, thrugh crossing over in a chiasma creating recombinant chromosomes.
Essentially you are shuffling alleles between chromosomes.
Example question:
Explain how crossing over can contribute to genetic variation [3]
- Sections of chromatids exchanged (1)
- Sections have different alleles (1)
- New combinations of (linked) alleles (1)
How can genetic diversity be compared within or between species?
- Frequency of measurable or observable characteristics
- Base sequence of DNA
- Base sequence of mRNA
What is a gene and where is it found?
A gene is a section of DNA found in the locus of a DNA molecule.
What is genetic diversity?
Number of different alleles of each gene
