inheritance

• gamete - sex cell
• fertilisation - when an egg cell meets a sperm and they fuse together
• sexual reproduction - when dna comes from two parents
• asexual reproduction - when dna comes form one parent
• zygote - a fertilised egg (contains a full set of chromosomes)
• chromosomes - a long strand of dna coiled up tightly found in the nucleus
• advantages of sexual reproduction

  • can get different offspring and genetic variation
  • if the environment changes, variation gives a survival advantage by natural selection
  • natural selection can be sped up by humans in selective breeding to increase food production
• disadvantages of sexual reproduction:

  • takes a lot of time and energy
  • more complex, so less reliable (e.g finding a mate, courtship, pollination)
• advantages of asexual reproduction:

  • only one parent needed
  • more time and energy efficient as do not need to find a mate
  • faster
  • many identical offspring can be produced when conditions are favourable (so could colonise a new area quickly or out compete other species)
• disadvantages of asexual reproduction:

  • lack of genetic variation means less likely to be able to adapt to changes in environment
  • e.g whole population more likely to be wiped out by a new disease
• why is it an advantage for a protist to reproduce asexually?

  they can very quickly reproduce so able to spread to a new host when conditions are not favourable
• genetic variation means things are bale to adapt to changing conditons which increases the chance of survival
• meiosis is a type of cell division which creates gametes
• During meiosis, the amount of dna (chromosomes) is halved from 46 to 23. there are two divisions instead of one
• meiosis takes place in the reproductive organs whereas mitosis takes place in all other cells
• the point of meiosis is to produce gametes whereas mitosis is used for growth and repair
• meiosis has 2 divisions whereas mitosis has 1
• meiosis is sexual whereas mitosis is asexual
• meiosis creates 4 daughter cells whereas mitosis creates 2
• the cells produced by meiosis are genetically non-identical whereas the ones produced by mitosis are genetically identical
• at the end of meiosis, there's 23 chromosomes in the cell whereas there's 46 in mitosis
• meiosis produces haploid cells (have single chromosomes) whereas mitosis produces diploid cells (have pairs of chromosomes)
• meiosis process:

  the pairs of chromosomes are halved then the two cells are copied and split again, leaving 4 non-identical daughter cells
• dna is a double stranded helix held together by complimentary bases pairs
• The basic units of DNA are nucleotides
• the structure of DNA is contained within chromosomes
• the repeating unit that dna is made out of are nucleotides
• a gene is a section of dna that codes for a protein
• there are four different nucleotides
• the four different bases are A, T, C, G
• A binds to T (apple tart) and C binds to G (chocolate gateau)
• Not all parts of dna code for proteins. non-coding parts of dna can switch genes on and off so variations in these areas of dna may affect how genes are expressed
• a genome is the entire genetic material of an organism
• structure of a nucleotide:

  there's a pentose sugar (which is a ribose of deoxyribose) which is attached to a phosphate and a nitrogenous base. The four bases are A,C,G,T
• Protein synthesis takes place in the ribosomes
• 3 bases code for 1 specific amino acid
• dna to protein:

  1. the double helix is unzipped
  2. mRNA is formed which uses complementary base pairing
  3. the mRNA leaves the nucleus
  4. a ribosome attaches at the start of the mRNA
  5. the ribosome moves along the mRNA reading every 3 bases
  6. each 3 bases code for 1 amino acid which is attached in the chain
  7. when the whole gene has been translated, the amino acid chain detaches
  8. the protein twists into the correct shape
• transcription is done by the mRNA
• translation is done by the ribosome
• enzymes have a unique shape with a specifc active site due to the order of amino acids in the proteins