Inheritance, Variation & Evolution

• Cell division that leads to identical cells being formed: Mitosis
• Gametes (sex cells) in animal reproduction: Sperm (male) and egg (female)
• Type of reproduction leading to a variety in offspring due to mixing of genetic information: Sexual reproduction
• Clone defined as genetically identical offspring resulting from asexual reproduction
• Cell division leading to non-identical cells being formed: Meiosis
• Number of chromosomes in each human gamete after meiosis: 23
• Structure of DNA: A polymer made up of two strands forming a double helix
• Specific section of DNA that codes for a particular protein: A gene
• Genome of an organism: The entire genetic material of that organism
• Importance of understanding the human genome:

  • Genes linked to different types of disease can be searched for
  • Inherited disorders can be understood / treated
  • Migration patterns of the past can be traced
• Before cell division, DNA in the cell gets stored in chromosomes
• Gene codes for a particular sequence of amino acids, which make specific proteins
• Embryo screening involves removing a cell from an embryo and analyzing its DNA to look for genetic disorders
• Explanation of a 'dominant allele': The characteristic is expressed if one or two copies of the allele are present
• Term for two of the same alleles (e.g., TT or tt): Homozygous
• Meaning of 'genotype': What alleles an organism has, e.g., Tt, TT, or tt
• Explanation of a 'recessive allele': The characteristic is only expressed if two copies of the allele are present
• Term for two different alleles (e.g., Tt): Heterozygous
• Meaning of 'phenotype': The characteristics an organism has, e.g., 'long hair', 'black fur', 'blue eyes', etc.
• Example of characteristics controlled by a single gene: Fur color in mice / red-green color blindness in humans
• Polydactyly is caused by a dominant allele
• Percentage chance of having a boy or girl: 50% male, 50% female
• Cystic fibrosis is a genetic disorder that affects cell membranes and causes mucus build-up in the air passages and pancreas
• Cystic fibrosis is caused by a recessive allele
• Most characteristics are determined by multiple genes interacting
• An allele is a version of a gene
• Variation refers to differences in the characteristics of individuals in a population
• Most mutations of DNA do not cause a change in phenotype
• Besides genotype, the environment affects the phenotype of an organism
• Genetic variation is caused by mutations
• Evolution is a change in the inherited characteristics of a population over time which may result in the formation of a new species
• Two organisms with a common ancestor are considered two different species when they cannot interbreed and produce fertile offspring
• Selective breeding involves choosing parents with desired characteristics, breeding them, selecting offspring with the desired characteristics, and continuing over many generations until a population with the desired characteristic is achieved
• Examples of "desired characteristics" in the selective breeding of animals: Animals which produce more milk/meat, domestic dogs of a gentle nature
• According to the theory of evolution through natural selection, all species of living things have evolved from simple life forms that first developed more than three billion years ago
• Speciation occurs through isolation of two populations, differences in environmental conditions or food availability, natural variation, mutations, and individuals better adapted to their environment surviving, reproducing, and producing offspring until populations become genetically different and can't interbreed
• Examples of "desired characteristics" in the selective breeding of plants: Improved yield, disease resistance
• Two examples of "desired characteristics" in the selective breeding of plants:

  • Disease resistance in food crops
  • Large / unusual flowers
• Negative consequences of selective breeding:

  • Inbreeding causes a reduction in gene pool
  • Reduced variation in genes means the population is less resistant to disease
  • Inbreeding can cause populations to have genetic defects
• Genetic engineering is taking a gene from one organism and inserting it into the genome of another