AQA Biology GCSE [B13] Verified Solutions

AQA Biology GCSE [B13] Verified Solutions What is a chromosome? A large molecule of DNA Gene A small section of DNA on a chromosome that codes for a particular sequence of amino acids that make a specific protein How many chromosomes do humans have? 46 (23 pairs) in most cells. Gametes have half of this number (23). Sexual reproduction The joining (fusion) of male and female gametes formed by meiosis producing genetic variation in the offspring as genetic material is mixed What is involved in asexual reproduction? 1 parent (no gametes). There is no mixing of genetic information, leading to genetically identical offspring (clones). Gametes Sex cells (eggs and sperm cells) which have half the number of chromosomes as an ordinary cell. Which process allows division of body cells? Mitosis What must happen before mitosis can occur? The DNA doubles (DNA replication) Outline the main stages of mitosis. 1) DNA replicates to produce 2 copies of each chromosome (4 complete sets) 2) Half chromosomes move to each end of the dividing cell and cell divides 3) Two daughter cells formed that are identical Compare the cells that are produced (daughter cells) by mitosis to the parent cell. They are genetically identical as the DNA is copied Which cells undergo meiosis and what do they form? Cells in the reproductive organs divide by osmosis to form the gametes (egg cells and sperm cells) What happens when a cell divides by meiosis to form gametes? The genetic material is copied and then the cell divides into 4 to form 4 genetically different cells (gametes), each with one set of chromosomes. How is mitosis different to meiosis? 1) Makes cells not gametes