B6

• Meiosis forms four non identical cells
• Mitosis forms two identical cells
• Sexual reproduction- joining together of male gametes and female gametes.
• An example of gametes in animals: egg cell and sperm cell.
• An example of gametes in plants: pollen and egg cells.
• Genetic information from each parent is mixed: produces variation in the offspring.
• Asexual reproduction involves one parent and no gametes joining together.
• Mitosis is involved in asexual reproduction.
• Genetic information doesn't mix in asexual reproduction- leads to clones (offspring are genetically identical)
• Examples of organisms that reproduce asexually: bacteria, some plants, and some animals.
• Meiosis- formation of four non-identical cells from one cell

  (how cells in reproductive organs divide to form gametes).
• Gametes have one copy of each chromosome.
• The process of meiosis- cell makes copies of chromosomes (doubles genetic information), divides into two cells (halves chromosomes into 46), cells divide again to produce four cells (23 chromosomes)
• After gametes produced- fuse in fertilisation (produce cells with 46 chromosomes), cells divide by mitosis, many cells are produced to form an embryo - cells differentiate.
• Advantages of sexual reproduction is: more genetic variation, allows us to use selective breeding.
• Variation in offspring is an advantage - if environment changes - organisms in the species will have a characteristic that allows them to survive (survival advantage).
• Variation decreases the chance of a whole species becoming extinct.
• Reason why selective breeding is an advantage: mixing two organisms with desirable features - offspring will have even more desirable characteristics- speeds up natural selection.
• Advantages of asexual reproduction- one parent is needed, faster, uses less energy, and in favorable conditions, produces a lot of offspring.
• Malarial parasites, some fungi and some plants use both methods of reproduction.
• Malarial parasites cause malaria- spread by mosquitos that reproduce sexually and then asexually reproduce in humans (in liver and blood cells).
• Fungi release spores- lands to produce more fungi,

  spores reproduce asexually, but when conditions change, they reproduce asexually to increase variation and avoid extinction.
• In plants, many reproduce sexually using pollen - reaches the egg cells in the female part of the plant. This is called pollination and it forms seeds.
• Strawberry plants asexually produce runners- new identical plants can grow off the runner.
• Daffodils asexually reproduce to grow bulbs- new bulbs can grow from the main one- produces new identical plants.
• Asexual reproduction is advantageous- they can reproduce even if the flowers are destroyed.
• DNA- double helix made of two strands of nucleotides held together by hydrogen bonds.
• DNA is a polymer.
• DNA stored in the nucleus on a chromosome and are triplet bases that code for a specific protein.
• Each gene codes for specific sequence of amino acids - the chain of amino acids makes a protein.
• A genome - total of all genes that code for all proteins within an organism
• Advantage of understanding genes - treatment of inherited disorders and tracing human migration patterns
• Chromosomes are long molecules of DNA - found in nucleus
• DNA is made up of nucleotides
• Nucleotides are made up of : one sugar molecule, one phosphate molecule and a base
• A-T and C-G are examples of complementary base paring
• Order of the bases forms a code - each group of three bases codes for an amino acids - amino acids join together - forms protein
• Different type or order of bases : determine what type of protein it is
• There are 20 parts of amino acids
• Non-coding DNA : do not code for proteins