Topic 7 - Genetics, populations, evolution and ecosystems

• Define genotype.→The genetic constitution of an organism
• Define phenotype.→The expression of the genes and its interactions with the environment
• Define homozygous.→A pair of homologous chromosomes carrying the same alleles for a single gene
• Define heterozygous.→A pair of homologous chromosomes carrying two different alleles for a single gene.
• Define recessive allele.→An allele only expressed if no dominant allele is present
• Define dominant allele.→An allele that will always be expressed in the phenotype
• Define codominant.→Both alleles are equally dominant and expressed in the phenotype.
• Define multiple alleles.→More than two alleles for a single gene
• Define sex-linkage.→A gene whose locus is on the X chromosome
• Define autosomal linkage.→Genes that are located on the same chromosome not sex chromosomes
• Define epistasis.→When one gene modifies or masks the expression of a different gene at a different locus.
• Define monohybrid→Genetic inheritance cross of a characteristic determined by one gene
• Define dihybrid→Genetic inheritance cross for a characteristic determined by two genes
• Define gene pool→All the alleles of all the genes within a population at one time
• Define allele frequency→The proportion of an allele within the gene pool
• The two Hardy-Weinberg equations→p2 + 2pq + q2 = 1 / p + q = 1
• Define disruptive selection→When individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles.
• What type of natural selection leads to speciation?→Disruptive
• Define speciation→Creation of new species
• Two types of speciation→Allopatric or Sympatric
• Allopatric speciation↓
• Geographically isolated leading to reproductive isolation
• Population physically separate into two
• Unable to reproduce
• Accumulation of differences over time
• Unable to interbreed to create fertile offspring
• Sympatric speciation↓
• Differences in behaviour leads to reproductive isolation
• Due to random mutation e.g change in courtship ritual or fertile at different times of the year
• Individuals will not reproduce together so no gene flow
• Accumulate different mutations so DNA is different
• Cannot interbreed to create fertile offspring
• Classified as two different species
• Define genetic drift→Change in the allele frequency within a population between generations
• What does substantial genetic drift lead to?→Evolution
• Define population→Group of organisms of the same species living in the same habitat
• Define habitat→Part of an ecosystem in which particular organisms live in
• Define community→All the populations of different species in the same area at the same time
• Define ecosystem→A community and the non-living components of an environment (biotic and abiotic factors)
• Define niche→An organism’s role within an ecosystem, including their position in the food web and habitat