Genetic Diagrams

• EARLY GENETICS

  •  The study of genetics began with observations made by Gregor Mendel.
  • After noticing that the flowers his pea plants were either violet or white, Mendel began to study the segregation of heritable traits.
  • Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants.
  • Remember that Mendel worked almost 150 years ago when nobody knew about genes or even the structures (chromosomes) that carry genes.
• Genes are located in chromosomes. Chromosomes come in pairs and there are thousands of genes in one chromosome. In humans, a cell's nucleus contains 46 individual chromosomes or 23 pairs of chromosomes. Half of the chromosomes come from one parent and half come from the other parent.
• Sexual reproduction

  1. Mother and father produce gametes (reproductive cells)

  2. Gametes have one copy of each chromosome

  3. Chromosomes from male and female gametes mix to produce offspring

  4. Offspring has pairs of chromosomes and two alleles for each gene
• Alleles


  Different versions of a gene
• If alleles are different

  Organism has instructions for two different versions of a characteristic but only shows one version
• Dominant allele


  The version of the characteristic that appears
• Recessive allele


  The characteristic caused by the recessive allele only appears if both alleles are recessive
• Genetic diagrams

  Dominant alleles are shown with a capital letter, recessive alleles with a small letter
• Genotype


  The alleles an organism has
• Phenotype


  The characteristics an organism displays
• Genetic Diagrams show the possible alleles in the offspring.

  Some characteristics are controlled by a single gene, e.g. blood group - this is called single gene inheritance.

  Genetic diagrams help to predict the phenotype of the offspring when you know the genotype of the parents.
• Your chromosomes control whether you're male or female

  • There are 23 pairs of chromosomes in every human body cell. The 23rd pair are labelled XY or XX.
  • These are sex chromosomes — they decide whether you turn out male or female.
  • XX - Female
  • XY - Male
• • Like other characteristics, sex is determined by genes.
  • The Y chromosome carries a gene which makes an embryo develop into a male as it grows, by stimulating the growth of testes. Females, who don't have a Y chromosome, don't have this gene and so they develop differently.
• Gametes or Sex cells

  • Sperm cell and egg cell
  • A type of cell that would only contain only one copy of a gene.
• How the genetic material is stored in an animal cell and how it is used to control what happens in the cell.

  • Stored in the nucleus
  • Some are stored in organelles, e.g. mitochondria and plasmids
  • Stored in chromosomes
  • Used as instructions to join amino acids together to make proteins/enzymes.
• Different ways how the genetic material is stored in a prokaryotic cell such as a bacterium.

  • Circular chromosomes or large loops of DNA
  • Plasmids
  • Stored in cytoplasms if there is no nucleus.
• Different forms of contraceptions:

  • Contraceptive pills
  • Condom
  • Female condom
  • Intra-urine device or  IUD
  • Diaphragm
  • Contraceptive implant
  • Surgical method or vasectomy/sterilisation
  • Rhythm method/Abstinence
• Rhythm method/Abstinence

  • no chemicals are used
  • there are no religious or ethical objections 
• Surgical method or vasectomy/sterilisation

  • a permanent solution (as they don’t want any more children)
  • prevents eggs and sperm meeting as tubes are cut
  • no sperm released with vasectomy 
  • egg cannot pass down oviduct with female sterilisation
• Contraceptive implant

  • works for up to 3 years
  • prevents ovulation / prevents ovum or egg being released.
• Diaphragm

  • prevents sperm entering the uterus
• Intra-urine device or  IUD

  • can remain in place for a long time or up to ten years
  • prevents sperm surviving in the uterus 
  • stops egg or ovum being fertilised 
  • prevents embryo implanting in the uterus
• Female condom

  • prevents sperm from reaching the ovum or egg
  • prevents sperm passing into the uterus or through the cervix.
• Condom

  • prevents sperm reaching the ovum or egg / prevent sperm entering the vagina or cervix or uterus.
  • protects against the spread of STIs 
• Contraceptive pills

  •  prevent ovulation / prevent release
  • of an ovum or egg 
  • thickens the mucus of the cervix so sperm can’t pass through