Biology paper 2

• Unit 6 - Inheritance, Variation and Evolution:

  • Reproduction:
  • Sexual Reproduction: fusion of two male and female gametes, with humans having egg and sperm cells, and plants having pollen and egg cells
  • Asexual Reproduction: division of one parent cell to produce genetically identical offspring (clones) in organisms like bacteria, plants, and some animals
• Advantages of Reproduction:

  • Sexual Reproduction:
  • Variation of offspring
  • Variation allows species to survive environmental changes through natural selection
  • Selective breeding to increase food production, etc.
  • Asexual Reproduction:
  • Only one parent needed, uses less energy, and is faster
  • Many identical offspring can be produced when conditions are favorable
• Both methods of reproduction are used in different scenarios like:

  • Malaria reproduces asexually in the human host but sexually in the mosquito
  • Fungi reproduce asexually by spores but also reproduce sexually for variation
  • Strawberry plants produce runners for identical plants and reproduce sexually as flowering plants to produce seeds
• Meiosis:

  • Process:

  1. Duplicates genetic material arranged in pairs in the cell

  2. First division creates two cells with one copy of chromosome pairs

  3. Second division separates chromosome pairs, producing four gametes with one set of chromosomes, all genetically different

  • Daughter cells fertilize with opposite sex gametes to produce cells with 23 chromosome pairs, which divide by mitosis to form an embryo
• DNA:

  • Stands for deoxyribonucleic acid, found in the nucleus of animal cells in long strands of chromosome pairs, with a double helix structure
  • Genes are small sections of DNA in a chromosome, coding for specific proteins with 20 amino acids used in the sequence
• Genomes:

  • Entire set of genetic material of an organism
  • Studying the entire genome allows advancements in medicine by identifying genes linked with diseases for treatment development and discovering human migration patterns
• The Structure of DNA:

  • Repeating units called nucleotides, consisting of a phosphate, sugar, and base
  • Complementary base pairing like A+T and C+G determines the order of amino acids in proteins
• Protein Synthesis:

  • Stages:

  1. Transcription: a copy of a gene is made in the nucleus (mRNA)

  2. mRNA passes into the cytoplasm

  3. Translation: mRNA attaches to a ribosome, amino acids bind to carrier molecules (tRNA), ribosomes read triple bases of mRNA for amino acid order
• Genetic Mutations:

  • Occur randomly or can be inherited, affecting protein formation by changing DNA base sequences and producing genetic variants
• Different Types of Mutations:

  • Insertions: new base inserted into DNA sequence, changing the way bases are read and amino acids coded
  • Deletions: random base deletion changing base sequence reading
  • Substitutions: random base changed to a different base, altering the sequence
• Definitions:

  • Gamete: reproductive cells
  • Chromosome: thin strands of DNA
  • Gene: small section of chromosome
  • Allele: different versions of the same gene
  • Dominant: always expressed, recessive only if two copies are present
  • Homozygous: both identical for a characteristic, heterozygous: both different
  • Genotype: combinations of alleles determining characteristics, phenotype: observable characteristics
• Inherited Disorders:

  • Cystic Fibrosis: genetic disorder causing thick mucus in air passages and pancreas, caused by recessive alleles requiring two for the disorder
  • Polydactyly: extra fingers or toes caused by a dominant gene, impossible to be a carrier
• Embryo Screening:

  • Definition: extracting DNA from an embryo to analyze genes for inherited disorders
  • Advantages: stop suffering of child and parents
  • Disadvantages: expensive, ethical concerns like creating desirable babies based on genetic traits
• Sex Determination:

  • Male: XY chromosomes, Female: XX chromosomes
• Variation And Evolution:

  • Types of Variation:
  • Genetic variation: genes from two parents
  • Environmental variation: conditions affecting phenotypes
  • Combination of both determining characteristics like height and diet
• Selective Breeding:

  • Process: choosing parents with desired characteristics to breed offspring with those traits
  • Examples: disease resistance in crops, more meat or milk in animals, gentle nature in dogs, large or unique flowers
• Genetic Engineering:

  • Definition: modifying an organism's genome by introducing genes from a different organism
• Disadvantages of inbreeding in some breeds:

  • Prone to disease or inherited defects due to reduction in the number of different alleles making gene forms too similar
• Genetic engineering is a process involving modifying the genome of an organism by introducing a gene from a different organism to give a desired characteristic
• Genetic engineering process:

  1. Genes from the chromosomes of the organism are cut out using enzymes

  2. They are inserted into a vector (bacterial plasmid or virus)

  3. The vector is used to insert the gene into required cells

  4. The cells are transferred at an early stage in development so they develop with desirable characteristics
• Examples of genetic engineering in industry:

  • Bacteria genetically modified to produce human insulin
  • Crops genetically modified to improve size, quality, and resistance to disease
  • Gene therapy for treating genetically inherited diseases
• Dilemmas of genetic engineering:

  • Changing an organism's genes might accidentally create problems passed onto future generations
• Pros of genetic engineering:

  • GM crops increase yield
  • GM crops provide needed nutrients to some populations
  • GM crops are already grown without problems
• Cons of genetic engineering:

  • Can reduce farmland biodiversity
  • Some people think they're not safe to eat
  • Transplanted genes may get out into the natural environment
• Plants can be cloned from tissue culture by placing a few plant cells in a growth medium with hormones to grow into new cloned plants
• Advantages of cloning plants from tissue culture:

  • Can be made quickly
  • Don't require lots of space
• Plants can be cloned from cuttings by gardeners taking cuttings from good parent plants and planting them to produce genetically identical copies
• Advantages of cloning plants from cuttings:

  • Can be made quickly
  • Cheap
• Embryo transplants work by taking sperm and egg cells from animals, artificially fertilizing the egg, splitting the embryo before cells specialize, and implanting them into the animal
• Adult cell cloning involves:

  1. Removing the nucleus from an unfertilized egg cell

  2. Inserting the nucleus of an adult body cell into the egg cell

  3. Stimulating the egg cell to divide and form an embryo

  4. Inserting the embryo into the womb of an adult female for further development
• Issues surrounding cloning:

  • Can preserve endangered species
  • Could lead to a greater understanding of embryo development, aging, and age-related disorders
  • Increase yield of plants and animals
  • Able to make clones of animals with medical advantages
• Theory of evolution and natural selection:

  • States all species evolved from simple life forms over three billion years ago
• Evolution is a change in the inherited characteristics of a population over time through natural selection, which may result in the formation of a new species
• Speciation is the development of a new species from the same species in different populations
• Isolation of a species can occur due to physical barriers like floods or earthquakes
• Reasons for speciation:

  • Conditions of both environments are different
  • Individuals with characteristics better adapted to the environment are more likely to survive and pass on these beneficial characteristics
• Wallace is most famous for his work on speciation and warning colors
• Mendel's experiment on pea plants:

  • First cross: Tall + Dwarf = All tall pea plant offspring
  • Second cross: Tall Tall Three tall + One Dwarf pea plant offspring
• Mendel's conclusion:

  • Characteristics in plants are determined by hereditary units passed on to offspring
  • Hereditary units can be dominant or recessive
• Classification of living organisms:

  • Organisms are divided into kingdom, phylum, class, order, family, genus, species