B6

• Allele: An alternative form of a gene
• Asexual reproduction: The production of offspring from a single parent by mitosis, resulting in clones of the parent
• Chromosome: Structures containing the DNA of an organism found in the nucleus
• Cystic fibrosis: A disorder of cell membranes caused by a recessive allele
• DNA: A polymer made up of two strands forming a double helix
• Dominant: An allele that is always expressed, even if only one copy is present
• Fertilisation: The fusion of male and female gametes
• Gamete: Sperm cell and egg cell in animals; pollen and egg cell in plants
• Gene: A small section of DNA that codes for a specific protein
• Genome: The entire genetic material of an organism
• Genotype: The combination of alleles
• Heterozygous: A genotype with two different alleles - one dominant and one recessive
• Homozygous: A genotype with two of the same alleles, either two dominant or two recessive alleles
• Meiosis: A two-stage process of cell division that reduces the chromosome number of daughter cells, producing gametes for sexual reproduction
• Mutation: A change in DNA
• Phenotype: The characteristic expressed due to the combination of alleles
• Polydactyly: Having extra fingers or toes caused by a dominant allele
• Recessive: An allele that is only expressed if two copies are present
• Sexual reproduction: The production of offspring by combining genetic information from the gametes of two parents, leading to variation in the offspring
• Mitosis:

  • Produces two daughter cells
  • Daughter cells are genetically identical
  • The cell divides once
  • Used for growth, repair, and asexual reproduction
• Meiosis:

  • Produces four daughter cells
  • Daughter cells are not genetically identical
  • The cell divides twice
  • Produces gametes for sexual reproduction
• Sex Determination:

  • Females carry two X chromosomes
  • Males carry one X and one Y chromosome
• Embryo screening: Genetic tests carried out on an embryo to see if it carries a faulty allele
• Evolution: A change in inherited characteristics of a population over time through natural selection
• Evolutionary tree: A method used to show how scientists believe organisms are related
• Extinction: The permanent loss of all members of a species
• Fossils: Remains of organisms from millions of years ago found in rocks
• Genetic engineering: The process by which scientists manipulate and change the genotype of an organism
• Natural selection: The process by which organisms better suited to an environment are more likely to survive and reproduce
• Selective breeding: Humans selecting animals or plants with desired characteristics for breeding
• Speciation: The process by which two species evolve from a single original species by natural selection
• Variation: Differences in characteristics of individuals in a population
• Variation may be due to differences in:

  • Genes inherited (genetic causes)
  • Conditions in which they developed (environmental causes)
  • Combination of genes and the environment
• Advantages of sexual reproduction:

  • Produces variation in offspring
  • Variation gives a survival advantage via natural selection
  • Natural selection can be increased by humans in selective breeding for increased food production
• Advantages of asexual reproduction:

  • Only one parent needed
  • More time and energy efficient
  • Faster than sexual reproduction
  • Many identical offspring can be produced when conditions are favorable
• Evolution by natural selection:

  • Variant advantageous in an environment leads to better competition, survival, and reproduction
  • Offspring inherit advantageous allele
• To reduce the rate of antibiotic-resistant strains:

  • Antibiotics should only be used when necessary
  • Patients should complete antibiotic courses
  • Agricultural use of antibiotics should be restricted
• forming Genes:

  • The template is copied from DNA and moves out of the nucleus
  • It binds to a ribosome
  • A carrier molecule binds to every three bases, carrying an amino acid joined to the previous amino
  • The amino acid strand folds into a 3D shape
• Cloning in Animals:

  • The gene needed is cut from DNA by enzymes
  • The plasmid is used to insert the gene into the required cell
  • Bacteria multiply many times
• Cloning in Plants:

  • Choose parents with desired characteristics
  • Select best offspring for breeding
  • Offspring are bred over many generations until desired result is achieved