Gentixs

• Sexual reproduction

  Genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
• Sexual reproduction


  1. Father and mother produce gametes (reproductive cells)

  2. Gametes only contain half the number of chromosomes of normal cells (haploid)

  3. At fertilisation, a male gamete fuses with a female gamete to produce a fertilised egg (zygote)

  4. Zygote undergoes cell division (by mitosis) and develops into an embryo

  5. Embryo inherits characteristics from both parents
• Meiosis


  A type of cell division that produces genetically different cells, unlike mitosis
• Meiosis Division 1


  1. Cell duplicates its DNA

  2. Chromosomes line up in pairs in the centre of the cell

  3. Pairs are pulled apart, each new cell only has one copy of each chromosome

  4. Each new cell will have a mixture of the mother's and father's chromosomes
• Meiosis Division 2


  1. Chromosomes line up again in the centre of the cell

  2. Chromatids (arms of the chromosomes) are pulled apart

  3. Four haploid daughter cells (gametes) are produced, each with a single set of chromosomes
• In humans, meiosis only occurs in the reproductive organs (ovaries and testes)
• Gametes

  Reproductive cells produced by meiosis, containing a single set of chromosomes (haploid)
• In flowering plants, male gametes are in the pollen and female gametes are in the ovaries
• DNA

  Molecule that carries the instructions for an organism's characteristics
• Nucleotides

  Repeating units that make up DNA strands
• DNA structure

  • Two strands coiled in a double helix
  • Each base on one strand pairs with a complementary base on the other strand
• Chromosomes

  Long, coiled up molecules of DNA found in the nucleus of eukaryotic cells
• Genes

  Sections of DNA on chromosomes that code for particular proteins
• An organism's complete DNA is called its genome
• Extracting DNA from fruit cells

  1. Mash fruit and mix with detergent and salt solution

  2. Filter mixture

  3. Add ice-cold alcohol to precipitate the DNA
• Alleles


  Different versions of the same gene
• Alleles

  • Organisms have two alleles for each gene, one from each parent
  • Alleles can be dominant or recessive
  • Dominant alleles overrule recessive alleles
• Genotype


  The combination of alleles an organism has
• Phenotype


  The characteristics an organism displays, determined by its genotype
• Monohybrid cross


  Shows how recessive and dominant traits for a single characteristic are inherited
• Genetic variation


  Differences between organisms of the same species, caused by genetic and/or environmental factors
• Genetic variation

  • Caused by different alleles and new alleles arising through mutations
  • Sexual reproduction combines alleles in different ways
• Environmental variation

  Variation in phenotype caused by environmental factors
• Mutations

  Changes to the base sequence of DNA, resulting in new alleles
• Most mutations are neutral and don't have a big effect on phenotype
• Some mutations have a small effect on phenotype, while others have a large effect
• New combinations of alleles may also interact to produce new phenotypes
• Human Genome Project


  Collaborative effort to map the entire human genome, identifying over 20,000 human genes
• Applications of the Human Genome Project

  • Prediction and prevention of diseases
  • Testing and treatment for inherited disorders
  • Development of new and better medicines
• There could also be drawbacks to the Human Genome Project, such as increased stress, gene-ism, and discrimination
• Sexual reproduction

  Genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
• Sexual reproduction

  1. Father and mother produce gametes (reproductive cells)

  2. Gametes only contain half the number of chromosomes of normal cells (haploid)

  3. Gamete fusion produces a fertilised egg (zygote) with the full set of chromosomes (diploid)

  4. Zygote undergoes cell division (mitosis) and develops into an embryo

  5. Embryo inherits characteristics from both parents
• Meiosis

  A type of cell division that produces genetically different cells (unlike mitosis)
• Meiosis

  1. DNA is duplicated

  2. Chromosomes line up in pairs in the centre of the cell

  3. Pairs are pulled apart, each new cell gets one copy of each chromosome

  4. Chromosomes line up again, chromatids are pulled apart

  5. Four haploid daughter cells (gametes) are produced, each genetically different
• In humans, meiosis only occurs in the reproductive organs (ovaries and testes)
• DNA

  Molecule that carries instructions for characteristics, makes up an organism's genome
• Nucleotide

  Repeating unit of DNA, consists of sugar, phosphate and one of four bases (A, T, C, G)
• DNA molecule

  • Two strands coiled in double helix
  • A always pairs with T, C always pairs with G (complementary base pairing)
• Chromosome

  Long, coiled up molecule of DNA found in the nucleus of eukaryotic cells
• Gene

  Section of DNA on a chromosome that codes for a particular protein