Chapter 8 - Meiosis and Variation
- Created by: stef17
- Created on: 04-05-16 09:08
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- Chapter 8 - Meiosis and Variation
- Variation
- Natural selection
- Stabilising selection is where the environemtn hasn't changed so the same alleles are being selected for
- Directional selection is where the environment has changed and one of the exrtreme forms of the species is at a selective advantage, so that allele becomes more common in the population
- Genetic drift
- Evolutionary change purely due to chance
- Common on island populations
- Speciation
- The formation of a new species
- Isolating mechanisms
- Ecological barriers
- Two species living in the same area at the same time but do not meet (crayfish)
- Temporal barriers
- Two species living in the same habitat but are not active at the same time of day or have different breeding seasons (shrubs)
- Reproductive barriers
- Unsuccessful breeding, due to any one of of the following mechanisms: different courtship, mechanical problems with mating (e.g. size) gamete incompatibility, zygote inviability or hybrid sterility
- Ecological barriers
- Species concept
- Biological species concept requires the species to have reproductive isolation
- Phylogenetic species concept just requires there to be a clear difference between the two species - but have come from a common ancestor
- Artificial selection
- Breeding animals for human's benefit
- Could be bad for the animal
- Natural selection
- Meiosis
- The process
- Meiosis I
- Halves the no of chromosomes,crossing over also happens in prophase I
- Meiosis II
- Similar to mitosis
- Meiosis I
- Independent assortment
- The mixing of genes from the organism's mother and father in diploid cells
- Total of 8,388,608 different combinations of alleles in a gamete
- The process
- Genes and inheritance
- Single gene inheritance
- The inheritance of a single gene (both copies)
- Whether an individual has CF is determined by this
- Homozygous vs heterozygous
- Codominance
- Blood group
- Two dominant alleles, both have an effect on the phenotype of the individual
- Sex linkage
- Male only diseases (e.g. haemophilia)
- Recessive alleles more likely to effect mmales (with only one X chromosome) than females
- Dihybrid inheritance
- Inheritance of two genes at the same time, but the genes are NOT on the same chromosme
- Autosomal linkage
- Inheritance of two genes that ARE on the same chromosome
- Epistasis
- One gene overridng another
- Equations and tests
- Hardy-Weinberg equation
- Chi (x2) test
- Single gene inheritance
- Genotype = the alleles an organism inherited, phenotype= the physical characteristics of the organism (e.g. coat colour)
- Variation
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