Inheritance, Variation and Evolution

• sexual reproduction produces genetically different cells
• the mother and father produce gametes (egg and sperm) by meiosis
• gametes are reproductive cells
• each gamete contains 23 chromosomes
• gametes in plants:

  • pollen
  • egg cells
• mixing genetic material leads to variety in offspring
• gametes are produced by meiosis
• asexual reproduction requires only one parent
• offspring is genetically identical to parent in asexual reproduction
• asexual reproduction happens by mitosis
• in asexual reproduction, a cell divides in two to make two new clone cells
• meiosis makes gametes with only half the original amount of chromosomes
• meiosis involves two cell divisions
• in humans, meiosis happens in reproductive organs
• when a cell divides to form gametes:

  • copies of the genetic information is made
  • the cells divide twice to form four gametes, each with a single set of chromosomes
  • all gametes are genetically different
• gametes join at fertilisation to restore the usual number of chromosomes
• DNA is the chemical that all genetic material in a cell is made from
• DNA contains coded information
• DNA is found in long structures, called chromosomes
• DNA is a polymer made of two strands which forms a double helix
• genes are a small secion of DNA found on a chromosome
• each gene tells the cell to make a particular sequence of amino acids to make a specific protein
• genome is the entire genetic material of an organism
• the human genome is important for science and medicine
• genomes allow scientists to identify genes linked to certain diseases
• genomes help to develop effective treatments
• genome helps trace human migration in the past
• chromosome is a long molecule of DNA found in the nucleus
• gene is a short section of DNA found on a chromosome which contains instructions needed for protein synthesis
• allele is an alternative version of a gene
• dominant alleles are alleles that is shown even if only one of that allele is present
• recessive alleles are alleles that are only shown if there is two of the same allele present
• homozygous is when an organism has two same alleles for a specific gene
• heterozygous is when an organism has two different alleles for a specific gene
• genotype is what type of alleles you have
• phenotype is the characteristic you have
• characteristics controlled by a single gene:

  • colour of fur in mice
  • colour blindness in humans
• some disorders are inherited, they are caused by the inheritance of certain bad alleles
• polydactyly is caused by a dominant allele (extra fingers or toes)
• cystic fibrosis is caused by a recessive allele