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Unit 2 - Making Gametes (H)

Cell division is one of the processes studied in GCSE Biology. This quiz focuses on one particular type, meiosis, which is used in the making of gametes. Gametes are the female and male sex cells - eggs and sperm.

The gametes are made in the ovary and testes by a special type of reduction cell division called meiosis. Normal body cells contain 23 paired chromosomes giving a total of 46. Gametes only have one copy of each chromosome so instead of 46 they only have 23. Each gamete has half the genetic content of the other cells in the body but when the egg and sperm fuse together during fertilisation, the chromosomes from the two gametes join together. The cell that is formed therefore contains a full set of 46 chromosomes as 23 pairs.

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This cell is called a zygote and soon begins to divide, making copies of itself and forming 2 cells, then 4 cells and so on. It does so through mitosis which means that each new cell that is formed contains the full set of 46 chromosomes. The chromosomes that we get from our parents are completely random. This means that no two offspring in a family will be genetically identical (unless they are identical twins that grew from the same zygote). Each child in a family will look a little like each parent and a little like each other but never identical.

Each gamete carries a chromosome that will determine the gender of the offspring. Eggs carry the X chromosome whilst sperm cells carry either the X or the Y chromosome. If an egg cell is fertilised by a sperm carrying the X chromosome, the offspring will be female as it will have two X chromosomes in its cells. The offspring will be male if the sperm carries the Y chromosome. It is the sperm that decides the sex of the offspring. Half of the sperm cells produced carry the X chromosome and half carry Y so, in a large population, probability means that about half of the babies born will be male and half will be female.

How does the body go about making sex cells? Are eggs made any differently to skin cells? See how much you remember about meiosis by taking this quiz.

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  1. Human body cells contain how many chromosomes?
    Different species have different chromosome numbers. For example, chimpanzees have 48 chromosomes in each body cell
  2. Human gametes (eggs or sperm) contain how many chromosomes?
    Each gamete contains half of the genetic material of the new individual
  3. At the start of meiosis, what is replicated?
    Before any cell can divide, the chromosomes replicate and make an extra copy of the DNA. This maintains the chromosome number for the species. One arm of each chromosome duplicates an exact copy forming an X-shaped structure
  4. Mitosis produces cells which are genetically...
    This is the type of cell division that occurs to produce cells with the full number of chromosomes
  5. Name the process by which the normal chromosome number is restored.
    At fertilisation, an egg containing 23 single chromosomes joins with the sperm also containing 23 single chromosomes to form a zygote with 46 chromosomes (23 pairs)
  6. Meiosis results in cells which are genetically...
    It is for that reason that variation of inherited features occurs.
  7. Variation takes place as a result of meiosis and is a big advantage of which type of reproduction?
    If every organism was identical to every other organism of the same species, it is possible that disease or a change in the environment would cause extinction
  8. Inside gametes, chromosomes are...
    Before genetics and cell division was understood, scientists were completely puzzled about what made gametes different to other cells
  9. Meiosis consists of how many cell divisions?
    This type of cell division forms cells with only half of the genetic information
  10. Meiosis results in how many gametes?
    In the first stages of meiosis, chromosomes make copies of themselves so (in humans) there are a total of 4 sets of chromosomes in the cell. These then separate, during two sets of cell division, into unpaired chromosomes so meiosis therefore creates 4 gametes.

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