Scholarship biology

• Polyploidy


  the heritable condition of possessing more than two complete sets of chromosomes
• Nondisjunction causes the formation of gametes with duplicate chromosomes (triploid, tetraploid)
• Autoploidy


  Within the same parental species (homozygous at every locus of genome)
• Allopolyploidy


  Result of hybridisation (varying degree of heterozygosity)
• Hybrid Vigour in plants means polyploid offspring of diploid parents are more vigorous and healthy
• Gene redundancy


  More copies of the same gene mean it is less likely to be affected by the deleterious effect of recessive mutations

  -diploid gamete permits masking of deleterious mutations by the presence of the dominant allele protecting the egg sac/pollen from developmental dysfunction
• Polyploidy allows the ability to diversify gene function over time, which gives more opportunity in evolutionary selection
• Polyploidy can disrupt favours self fertilisation favouring asexual reproduction
• Polyploidy disadvantages


  Cellular disruption leads to a disproportional increase in nuclear volume compared to nuclear envelope surface area.

  -disrupts chromosome/nuclear component interactions

  -peripheral positioning of key chromatin components like telomeric and centromeric heterochromatin can be disturbed
• Polyploidy disadvantages


  Mitotic/meiotic changes: increases spindle irregularity, leading to chaotic chromatid segregation and aneuploidy.

  • autopolyploids can form various chromosome arrangements at meiosis
  • allopolyploids require constrained chromosome pairing for balanced gamete formation
• Polyploidy disadvantages


  Gene expression: Copies of genes may not be uniformly expressed or some genes may be sensitive to odd-numbered ploidy
• Polyploidy disadvantages


  Epigenetic instability: might trigger widespread change in epigenetic regulation, affecting phenotype and gene expression
• Temporal isolation


  Different species don't mate because they are active at differents times of day or season
• Ecological isolation


  Individuals mate in their preferred habitat and so do not meet individuals of other species in different ecological preferences
• Behavioural isolation is when species have different behaviours that prevent them from interbreeding
• Mechanical isolation is where copulation is attempted but the transfer of sperm does not take place
• Gametic incompatibility is when two gametes are incompatible and cannot produce fertilized offspring
• Zygotic mortality: egg is fertilised but doesn't develop
• Hybrid inviability is where the embryo forms but of reduced viability
• Hybrid sterility is when a hybrid is sterile but the parents are fertile
• Hybrid breakdown is when F1 hybrids are fertile but F2 (further hybrid generations and backcrosses) may be sterile
• Reproductive isolation is an external barrier to reproduction between two incipient species preventing the formation of a new species
• Allopatry ‐ the process of a species becoming geographically isolated from its original range.
• Importance of isolation

  1. Prevents gene flow between populations
  2. gene flow favours the average
  3. dilution of alleles by gene flow
  4. With gene flow it takes a long time for mutant alleles to be visible
• Isolation allows:

  1. inbreeding - more homozygosity of mutant alleles
  2. non-random mating - leads to more inbreeding
• Peripatric speciation


  Form of allopatry that occurs on the periphery/outskirts of a population

  -low ability to live in extreme environments
• Parapatric speciation


  occurs inside a population due to a change in environment by allopatry or sympatry
• Causes of prezygotic RIMs

  -gametes unable to detect each other

  -gametes don't recognise each other (receptors accept certain sperm)

  -sexual organs change size, shape, location

  -Mating rituals and vocabulary change

  -chromosomal incompatibility
• Postzygotic RIMs are where the zygote forms but the individual is no longer fertile.

  -shortened life expectancy

  -genetic mutations

  -lethal mutations

  -ostracisation from population due to behaviour difference
• Homologous structures are in the same locus in different animals sharing a common ancestor but have adapted to serve different purposes
• Analogous structures


  Solve the same problem with different structures at different times e.g (flight)
• Sub-optimal design is where a structural component of the body is almost perfect for it's function but has one weak point where it completely fails
• Gradualism


  the gradual change in the population form one specific form to another
• Punctuated equilibrium is a model of evolution where species are not constantly changing, but instead, go through periods of rapid change
• Convergent evolution


  two species begin to look and behave this same due to the same selection pressures, but never become the same species
• parallel evolution


  Two unrelated species with the same niche evolve in similar ways
• Adaptive radiation is the rapid diversification of species because many niches became available
• introgression


  the transfer of genetic material from one species into the gene pool of another