Biology Reproduction and Genetics Overview

Reproduction

• Many species of fungi can reproduce both sexually and asexually.
• Asexual reproduction produces spores which are genetically identical.
• Sexual reproduction increases variation and avoids extinction.
• Strawberry plants reproduce asexually by producing runners.
• Daffodils reproduce asexually by growing new bulbs from the main bulb.
• Plants can reproduce asexually even if their flowers have been destroyed.

DNA and The Genome

• The genetic material in the nucleus of a cell is composed of DNA.
• DNA is a polymer made up of two strands twisted to form a double helix.
• DNA is contained within chromosomes in the nucleus.
• A gene is a section of DNA that codes for a specific protein.
• The genome is all the genes coding for all the proteins in an organism.
• The study of the human genome helps understand gene-disease links, inherited disorder treatments, and human migration patterns.

Understanding Genetics

• DNA stands for deoxyribonucleic acid and it is a polymer that contains instructions for the body.
• Chromosomes are structures made up of long molecules of DNA found in the nucleus of a cell.
• DNA is made up of many small parts called nucleotides.
• Breeding those with similar desirable characteristics leads to a reduction in the gene pool.
• This reduces the number of different alleles, making the species vulnerable to environmental changes or disease.
• A small gene pool increases the chance of genetic defects presenting in offspring.

Genetic Engineering

• Genetic engineering involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
• Plant cells have been engineered for disease resistance or larger fruits.
• Bacterial cells have been engineered to produce substances useful to humans, such as human insulin.
• The process of genetic engineering involves:
  • "Cutting out" genes using restriction enzymes, which creates "sticky ends".
  • Cutting a virus or bacterial plasmid using the same restriction enzyme to create sticky ends.
  • Joining the gene and loop with DNA ligase enzymes.
  • Placing the combined loop in a vector, such as a bacterial cell.
  • Identifying bacteria resistant to antibiotics, as these will be producing the modified gene.
• In plants, the vector is placed in meristematic cells which creates identical copies of the modified plant.
• Genetically modified crops can be resistant to insects and herbicides which can increase yield by reducing crop death.
• Gene therapy uses genetic engineering to transfer normal genes into patients to correct faulty proteins.

Theory of Evolution

• Charles Darwin, a scientist and naturalist, put forward the theory of evolution.
• Darwin's theory is supported by experimentation, geology, and discovery of fossils.
• Darwin's theory states that:
  • Variation exists within species due to DNA mutations.
  • Organisms best suited to the environment are more likely to survive and reproduce.
  • Beneficial characteristics are passed on to the next generation.
  • The frequency of advantageous alleles increases in the population over time.
• Darwin's theory contradicted the idea of God being the creator of all species.
• The mechanism of inheritance and variation was not known at the time.
• Jean-Baptiste Lamarck believed that changes during an organism's lifetime were inherited by offspring.
• Lamarck's theory was proven wrong when it was understood that environmental changes are not passed on through sex cells.
• Darwin's theory was supported by genetics as it provided an explanation for the inheritance of beneficial characteristics.
• Fossil evidence shows how developments in organisms arose slowly.

Speciation

• Speciation is the process of a new species developing through the selection of different alleles.
• Alfred Russel Wallace developed the theory of speciation, and therefore evolution by natural selection.
• Wallace believed that individuals without characteristics for survival would die out.
• Wallace and Darwin published joint studies, although Darwin received more recognition for the theory.
• The process of speciation involves:
  • Variation within a population due to genetic mutations.
  • Natural selection of alleles providing a survival advantage.
  • Isolation of populations, for example by physical barriers.
  • Different alleles becoming advantageous in a new environment.
  • Increased genetic variation over time between populations.
  • The inability to interbreed to produce fertile offspring, which signifies a new species.

Gregor Mendel

• Gregor Mendel trained in mathematics and natural history.
• Mendel observed characteristics inherited by plants in monastery gardens.
• Mendel performed breeding experiments on pea plants to observe inheritance.
• Mendel concluded:
  • Offspring inherit "hereditary units".
  • One unit is received from each parent.
  • Hereditary units can be dominant or recessive.

Resistant Bacteria

• Bacteria are labelled resistant when they are not killed by antibiotics that were previously used as cures.
• Mutations during reproduction can lead to new genes, such as the gene for antibiotic resistance.
• Exposure to antibiotics creates a selection pressure, favoring bacteria with antibiotic resistance.
• Antibiotic resistant bacteria reproduce and pass on the advantageous gene to their offspring, increasing the population.
• Bacterial diseases spread rapidly because people are not immune to new resistant bacteria.
• MRSA, a superbug resistant to many antibiotics, is common in hospitals.
• Factors contributing to the development of antibiotic resistance:
  • Prescribing antibiotics for viral or non-serious infections.
  • Using antibiotics for specific bacteria.
  • Not completing antibiotic courses.
  • Overuse of antibiotics in agriculture.
• Factors contributing to the transmission of antibiotic resistant bacteria include:
  • Maintaining high standards of hygiene in hospitals.
  • Regular hand-washing.
  • Regular sterilisation of medical clothing.
• It is difficult to keep up with the development of resistant strains due to slow and costly development of new antibiotics.