what is a locus?
gene occupying a specific section of a chromosome
what is codominance?
when both alleles are homozygous dominant, both are expressed in the phenotype
what is sex linkage?
characteristics that are influenced by genes on the sex chromosomes (usually X chromosome as it has more genes)
what is an example of a sex-linked disease?
haemophilia
what is autosomal linkage?
when both alleles occur on the same autosome so the alleles are inherited together unless crossing over occurs
what is incomplete dominance?
neither allele is dominant hence both alleles contribute to the phenotype
what is epistasis?
interaction between different genes, where the expression of one gene is affected by the expression of another gene at a different locus
what is mendels expected ratio of dihybrid crosses?
9:3:3:1
what factors affect evolution?
- sexual selection
- gene flow
- genetic drift
- natural selection
what is a genetic bottleneck?
50% or more of a population are killed which reduces the gene pool
what is the founder effect?
a new colony has started by a few members of the original population
what are two isolating mechanisms?
- geographical isolation
- reproductive isolation
what is the selective breeding process?
- select organisms with best characteristics
- breed them and select the best offspring
- continue over several generations
what are the pros and cons of selective breeding?
pros: maximise crop yield
cons:
- smaller gene pools
- animal discomfort/ethical problems
- inbreeding
why is a large gene pool necessary?
effect of chance variation in gene frequencies are minimised
what events are involved of the formation of a new species?
- gene pool
- selection pressures
- change in the environment
how can autosomally linked genes be arranged?
- different segments of the same chromatid
- same place on opposite chromatid that might have a different allele
what is meant by the term monogenic inheritance?
inheritance of a single gene
what is meant by the term gene pool?
the total number of different genes present in an interbreeding population
what is meant by the term genetic drift?
a change in the allele frequency of a population due to chance
what is stated by the Hardy Weinberg principle?
in a stable population with no disturbing factors, the allele frequencies of a gene will remain the same from one generation to the next
list the conditions which must be met for the Hardy Weinberg principle to apply
- there is no mutations, selection or migration
- the population is very large or big and genetically isolated
- mating is random
