Reproduction

• Types of reproduction


  • Sexual reproduction
  • Asexual reproduction
• Sexual reproduction


  • Involves two parents
  • Cell division through meiosis
  • Joining (fusion) of male and female sex cells (gametes)
  • Produces non-identical offspring that are genetically different to parents
  • Results in wide variation within offspring and species
• Meiosis


  • A type of cell division that makes gametes in the reproductive organs
  • Halves the number of chromosomes in gametes, and fertilisation (joining of two gametes) restores the full number of chromosomes
• Asexual reproduction


  • Involves one parent
  • Cell division through mitosis
  • No fusion of gametes
  • Produces offspring that are genetically identical to parent (clones)
  • No mixing of genetic information
• Fertilised cell division


  1. Divides by mitosis, producing more cells

  2. As the embryo develops, the cells differentiate
• DNA


  • Genetic material in the nucleus of a cell
  • Made up of two strands forming a double helix
  • Contained in structures called chromosomes
• Gene


  A small section of DNA on a chromosome that codes for a specific sequence of amino acids to produce a specific protein
• Genome


  The entire genetic material of an organism
• The whole human genome has been studied, and has allowed scientists to search for genes linked to different diseases, understand and treat inherited disorders, and trace human migration patterns from the past
• Inherited disorders


  • Some disorders are due to the inheritance of certain alleles
  • Polydactyly (extra fingers or toes) is caused by a dominant allele
  • Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele
• Gamete


  Specialised sex cell formed by meiosis
• Chromosome


  Long molecule made from DNA, found in the nucleus of cells
• Gene


  Sequence of DNA that codes for a protein - some characteristics are controlled by a single gene, but most are controlled by multiple genes interacting
• Allele


  Different forms of the same gene
• Dominant


  Allele that only needs one copy to be expressed (it is always expressed)
• Recessive


  Allele that needs two copies present to be expressed
• Homozygous


  When an individual carries two copies of the same allele for a trait
• Heterozygous


  When an individual carries two different alleles for a trait
• Genotype


  Combination of alleles an individual has
• Phenotype


  Physical expression of the genotype - the characteristic shown
• Genetic cross


  1. Considering the offspring that might result from two known parents

  2. Punnett squares can be used to predict the outcome of a genetic cross, allowing us to see the genotypes the offspring might have and their phenotypes
• Normal human body cells contain 23 pairs of chromosomes - one of these pairs determines the sex of the offspring
• In human females the sex chromosomes are the same (XX, homozygous), and in males they are different (XY, heterozygous)
• The probability of offspring being male or female is always 50% in humans as there are two XX outcomes and two XY outcomes