Inheritance

• Sexual reproduction

  • Involving 2 parents and fusion of gametes and mixing of chromosomes.
  • The offspring contains a mixture of genes and is genetically different to either parents.
  • Occurs by meiosis
• Fertilisation

  • The fusion of the nucleus of a male gamete with the nucleus of a female gamete.
  • When the gametes combine, they merge the two sets to form 46 chromosomes. Referred as a diploid.
  • Gametes are made by meiosis
• Asexual reproduction

  • Involves one parent and there is no fusion of gametes. Because there is no mixing of genetic information.
  • The offspring is genetically identical to the parent.
  • Occurs by mitosis
• The genome

  • Is the entire set of genetic material of an organism.
• Genes

  • A small section of DNA on a chromosome that codes for a particular sequence of DNA.
• Chromosomes

  • Two long strands of DNA coiled up to form a chromosome.
  • Human body cells contain 23 pairs of chromosomes.
• DNA

  • A double helix polymer, made up of two strands forming a twisted ladder shape.
• Gene identification

  • Identifying genes linked to different disorders.
• Mutations

  • A mutation is a permanent change in the nucleotide of DNA.
• Alleles

  • Different forms of a particular gene.
  • Peoples characteristics are determined by the alleles.
  • They are either dominant or recessive.
• Dominant Allele

  • Is always expressed, regardless of the other allele.
  • It only needs one copy to be present.
• Recessive allele

  • Only expressed if the other allele is also recessive.
  • Represented by a lower case letter e.g bb
  • Needs two copies for it to be present
• Polydactyly

  • Is a disorder involving extra fingers or toes.
  • Caused by a dominant allele.
• Recessive allele

  • Is caused by a recessive allele.
  • Is a disorder of the cell membrane, it causes mucus to build up in the lungs and digestive system.
• Heterozygous


  If the two alleles of a particular gene are different.
• Homozygous

  • If the two alleles of a particular gene are identical.
• Embryonic screening

  • Is a form of genome screening.
  • Looking for genes that may make that person susceptible to genetic disorders.
• Advantages of screening

  • Screening ensures the implanted embryos are healthy.
  • Prevent suffering
  • Financial saving, reduction in disorders that need to be treated.
• Disadvantages of screening

  • Expensive
  • Ethics, the embryos that are of no use are destroyed which is considered as unethical and against religious views.
  • Parents become selective
• A gamete

  • Reproductive cells e.g sperm cell
  • Haploid (23 chromosomes)
• Meiosis

  • 2 Cell divisions
  • Before the cell divides, the genetic information is duplicated, forming two armed chromosomes.
  • After replication, the chromosomes arrange into pairs.
  • First division involved chromosomes lining up the centre of the cell.
  • The pairs are pulled apart so each new cell only have 1 copy of each chromosome.
  • Second division involves when the chromosomes line up again and cell divides.
  • Forming 4 gametes which are genetically different as the chromosomes get shuffled up.
• Genotype

  • The combination of alleles that a person as for a particular trait.
• Phenotype

  • The observable characteristics of an organism.
  • For example, eye colour
• Sex determination

  • The human body cells has 23 pairs of chromosomes
  • 22 pairs of chromosomes control characteristics only, but one of the pairs carry the genes that determines the sex.