Genetics

• Sexual reproduction


  The fusion of male and female gametes to form a zygote
• Gamete


  A sex cell (Sperm in males and eggs in females)
• Types of cell division


  • Mitosis
  • Meiosis
• Haploid cells


  A gamete that only contains one set of chromosomes
• Meiosis


  Reduction division in a cell in which the chromosome number is halved from diploid to haploid
• Mitosis


  Used in asexual reproduction
• Meiosis


  Used in sexual reproduction
• Advantages of asexual reproduction


  • Doesn't require a mate
  • Identical offspring
  • Faster
• Advantages of sexual reproduction


  • Artificial selection
  • Variation in offspring
• Structure of DNA


  • A polymer made up of two strands coiled to form a double helix
  • Nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar
• Sex-linked genetic disorders


  • Most genetic disorders need two recessive alleles to inherit the disease
  • If a person has one, they are a carrier of the disease, which means they can pass it to their children without having symptoms of the disease themselves
• Transcription stage of protein synthesis


  1. The double helix's weak hydrogen bonds are broken by an enzyme

  2. RNA polymerase attaches to non-coding DNA in front of the gene

  3. Free RNA nucleotides form hydrogen bonds with the exposed DNA nucleotides by complementary base pairing to form a strand of mRNA

  4. The mRNA is ready to leave the nucleus and enter the ribosome
• T base in DNA


  Replaced by the U base in mRNA
• Translation stage of protein synthesis

  1. The mRNA strand attaches to the ribosome

  2. The ribosome lines up a complementary molecule of tRNA for every three mRNA bases. Every three bases are codons

  3. tRNA transports amino acids to the ribosome

  4. Used tRNA molecules exit the ribosome and collect another specific amino acid

  5. A chain of hundreds of other amino acids in the correct order is made to form a polypeptide
• Phenotype


  The visible characteristics of an organism which occur as a result of its genes
• Non-coding DNA


  Some regions are not as good as binding to RNA polymerase, affecting the protein produced and the phenotype
• Genome


  The entire DNA of an organism
• How bases in DNA decide amino acid order

  1. Each codon codes for one particular amino acid

  2. The number and order of the amino acids is decided by the number and order of the codons

  3. The amino acids join together to make a molecule

  4. This folds in order to make specifically shaped protein such as enzymes
• Zygote


  A fertilised egg cell
• Chromosome


  The structure that is made of DNA that codes for all characteristics in an organism
• Allele


  Different forms of the same gene
• Genotype


  The alleles that an organism has for a particular characteristic, usually written as letters
• Homozygous


  A genotype that has two identical alleles
• Causes of variation that influence phenotype


  • Genetic variation
  • Environmental variation
• Heterozygous


  A genotype that has two different alleles
• Dominant


  An allele that expresses himself no matter whether it has a matching allele or is a partner
• Most features are the result of multiple genes rather than single gene inheritance
• Monohybrid inheritance


  The inheritance of a single characteristic
• The Human Genome Project enabled searching for genes linked to different types of disease, understanding inherited disorders and treatments, and tracing human migration from the past
• Genetic variation


  Different characteristics as a result of mutation and sexual reproduction
• Environmental variation


  Different characteristics caused by an organism's environment
• How to extract DNA from fruit


  1. Chopping up the kiwi fruit

  2. Leave it in the salt and detergent mix

  3. This breaks open the membranes

  4. This lets the DNA and all the cell contents out
• Before Mendel's discovery, many people believed that traits in offspring resulted from a blending of the traits of each parent, and there was no knowledge of dominant and recessive alleles or what a gene was
• Changes in the variation of the gene cause differences in inherited characteristics as a result of alleles
• How sex of offspring is determined at fertilisation


  Men have a pair of X and Y chromosomes. Women have X and X. There is a 50% chance for each gender to develop
• Autosomes


  Chromosomes that do not determine sex
• Role of meiosis


  • Meiosis is a type of cell division that doesn't produce identical cells. It produces gametes
  • The gamete-making cell is diploid. The chromosomes replicate. The cell divides into two and then two again. Each of the final four daughter cells has half the number of chromosomes - this results in genetically different haploid gametes
• Researchers managed to map over 20,000 human genes in the Human Genome Project, with the aim of finding every single human gene
• The complementary base pairs of DNA are A-T and G-C
• There is usually genetic variation within a population of a species and these arise through mutations