Topic 7 - genetics

• Define genotype:

  the genetic constitution of an organism
• Define phenotype:

  The expression of an organisms genetic constitution, along with its interaction with the environment
• What is an allele?

  A different type of the same gene
• Define dominant allele:

  Allele whose characteristic will always appear in the phenotype (only needs 1 to be expressed)
• Define recessive allele:

  An allele whose characteristic only appears in the phenotype if no dominant allele is present. (2 need to be there)
• Define coodominant alleles:

  Two dominant alleles that are both expressed in the phenotype, appear together (red + white roses -> pink rose)
• What does homozygous mean?

  Both alleles are dominant or both are recessive
• What does heterozygous mean?

  One allele is dominant while the others recessive
• Define monohybrid inheritance:

  One phenotypic characteristic is controlled by a single gene
• Define dihybrid inheritance:

  Two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
• What is meant by sex-linkage?

  When the allele is located on one of the sex chromosomes (X or Y), so it's expression depends on the sex of the indervidual
• Why are males more likely to express sex-linked alleles?

  • Most sex-linked chromosomes are on the X chromosome
  • Males only have one X chromosome
  • So are going to express the allele even if its recessive
• Which parent would a male inherit sex-linked chromosomes from?

  His mother as its most likely on the X chromosome
• Define autosomal linkage:

  Where two or more genes are located on the same somatic chromosome. So only one homologous pair is needed for all 4 alleles to be present. (Gene that arnt linked need 2)
• Define epistasis:

  Where two non-linked genes interact, with one gene either suppresses or masks another gene
• What are the 2 types of epistasis? Define each:

  • Recessive epistasis - two homozygous recessive alleles mask the expression of another allele
  • Dominant epistasis - one Dominant allele masks expression of multiple alleles
• What is the chi-squared test?

  A statistical test to show whether the difference between observed and expected data is due to chance or not
• Define population:

  All the organisms of a particular species that live in the same place
• Define gene pool:

  The range of different alleles that are present for a particular locus within a popoupation
• Define allele frequency:

  The proportions of a certain allele within a gene pool
• What is the Hardy-Weinberg principle?

  Allows used t estimate the frequency of alleles in a population, as well as if allele frequency I'd Changing over time
• What are the assumptions made by the hardy-weinberg principle?

  • No mutations to create new alleles
  • No migration
  • No selection
  • Random mating
  • Large population
• Hardey-weinberg equation:

  p + q = 1

  p² + 2pq + q² = 1

  p = freq of dominant allele (² homozygous dominant)

  q = freq of recessive allele

  (² homozygous recessive)

  2pq = heterozygous
• What are the causes of phenotypic variation within a species?

  • Random mutation
  • Random fertilisation
  • Independently segregation
  • Crossing over
• What does natural selection occur?

  • Predation
  • Disease
  • Competition
• What are the stages of natural selection?

  1. Selection pressure
  2. Random mutation
  3. Beneficial allele
  4. Reproductive success
  5. Allele frequency
  6. Gene pool
  7. Evolution by natural selection
• When does stabilising selection occur? What phenotypes are favoured?

  • When environmental condition remian the same
  • Individuals closes to mean are favoured
• When does directional selection occur? What phenotypes are favoured?

  • Occurs when environmental conditions change
  • Phenotype that favours new conditions are favoured
• When does disruptive selection occur? What phenotypes are favoured?

  • The opposite of stabilising but when environments constant
  • Favours both extremes but not the mean
• Define allopatric speciation:

  1. When a population is split by a geographical barrier (river & mountain etc) and there are different selective pressures on them.
  2. Mutations build up
  3. Until the two groups can no longer reproduce to have fertile offspring
• What is sympatric speciation?

  1. When a population becomes reproductive isolated from one another due to a non-physical barrier (different flowering times)
  2. Different selective pressures
  3. Mutations build up until both groups can no longer reproduce to have fertile offspring
• Define genetic drift:

  A change ina populations alleles that occurs down to chance
• Outline the process of genetic bottleneck:

  1. A catastrophe happens and wipes out the majority of a population, so only a few alleles remain
  2. These members reproduce
  3. The population of has the alleles from the survivers
  4. Reduced genetic diversity
• Why does genetic drift effect smaller populations rather than larger ones?

  Gene pools smaller, so there are less alleles available and any change in frequency has a bigger effect
• Define community:

  All the different species that live in one area and interact with each other
• Define ecosystem:

  All the living organisms found within an area, combined with any abiotic aspects of there environment.
• Define abiotic and biotic: Give an example:

  • Abiotic - non-living (light intensity, temperature, soil pH)
  • Biotic - living (predators, diseases)
• Define habitat:

  The place where an organism lives within an ecosystem
• Define niche:

  • The role of a species within its habitat
  • If multiple species occupy the same niche they will compete
• What is meant by carrying capacity?

  The maximum size of a population an ecosystem can support