sexual reproduction and meiosis
- Created by: tia5sos
- Created on: 22-11-20 15:08
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- sexual reproduction and meiosis
- sexual reproduction produces gentically different cells
- sexual reproduction is where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
- in sexual reproduction, the mother and father produce gametes - in animals these are sperm and egg cells.
- gametes only contain half the number of normal cells - they are haploid. Normal cells (with the full number of chromosomes) are called diploid.
- at fertilisation, a male gamete fuses with a female gamete to produce a fertilized egg. The fertilised egg ends u with the full set of chromosomes (so it is diploid)
- the fertilised egg the undergoes cell division (by mitosis) and develops into an embryo.
- the embryo inherits characteristics from both parents as it is a mixture of chromosomes (and therefore genes) from it's mum and dad.
- gametes are produced by Meiosis
- meiosis is a type of cell division. Its different to mitosis because it doesn't produce identical cells. In humans, meiosis only happens in the reproductive organs (ovaries and testes).
- 1. before the cell starts to divide, it duplicates its DNA (so there's enough for each new cell). One arm of each x-shaped chromosome is an exact copy of the other arm.
- 2. in the first division in meiosis the chromosomes line up in pairs in the centre of the cell. One chromosome in each pair came from the organism's mother and one came from its father.
- 3. The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some of the fathers chromosomes and some of the mother chromosomes go into each new cell.
- 4. Each new cell will have a mixture of the mother's and father's chromosomes. Mixing up the genes like this is really important - it creates genetic variation in the offspring.
- 5. in the second division the chromosomes line up again in the centre of the cell. It's a lot like mitosis. The arms of the chromosomes are pulled apart.
- 6. You get 4 haploid gametes - each only has a single set of chromosomes. The gametes are all gentically different.
- sexual reproduction produces gentically different cells
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