Mitosis and Meiosis

Mind Map by , created over 5 years ago

GCSE Science (Biology Additional) Mind Map on Mitosis and Meiosis, created by sian.allison on 01/18/2014.

Created by sian.allison over 5 years ago
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Mitosis and Meiosis
1 Mitosis
1.1 Our cells need to be able to divide
1.2 Mitosis makes new cells for Growth and Repair
1.2.1 Body cells normally have two copies of each chromosome-one from the mother and one from the father. So humans have two copies of chromosomes 1 and chromosomes 2 etc
1.2.2 The 23rd pair of chromosomes are different
1.2.3 When a body cell divides it needs to make new cells identical to the original cells-with the same number of chromosomes This is mitosis its used when plants and animals want to grow or replace cells that have been damaged
1.2.4 Mitosis is when a cell reproduces itself by splitting to form two identical offspring In a cell thats not dividing, the DNA is all spread out in long strings If the cell gets a signal to divide, it needs to duplicate its DNA - so theres one copy for each new cell. The DNA is copied and forms X shaped chromosomes. Each "arm" of the chromosome is an exact duplicate of the other The chromosomes then line up at the center of the cell and cell fibres pull them apart. The two arms of each chromosomes go to opposite ends of the cell Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells Lastly the cytoplasm divides You now have two new cells containing exactly the same DNA - they are identical
1.3 Asexual Reproduction also uses Mitosis
1.3.1 Some organisms also reproduce by mitosis e.g. strawberry plants form runners in this way which become new plants This is an example of asexual reprodcution The offspring have exactly the same genes as the parent theres no variation
2 Meiosis
2.1 Gametes have half the usual number of chromosomes
2.1.1 During sexual reproduction two cells called gametes (sex cells) combine to form a new individual Gametes only have one copy of each chromosome. This is so that you can combine one sex cell from the mother and one sex cell from the father and still end up with the right number of chromosomes in the body cells. For example human body cells have 46 chromosomes. The gametes have 23 chromosomes each so that when an egg and sperm combine you get 46 chromosomes again The new individual will have a mixture of two chromosomes so it will inherit features from both parents. This is how sexual reproduction produces variation
2.2 Meiosis involves two divisions
2.2.1 To make new cells which only have half the original number of chromosomes cells divide by meiosis. It only happens in the reproductive organs e.g. orvaries
2.3 Meiosis produces cells which have half the normal number chromosomes
2.3.1 As with mitosis before the cell starts to divide it duplicates its DNA - one arm of each chromosome is an exact copy of the other arm In the first division in meiosis (there are two divisions) the chromosome pairs line up in the center of the cell 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 mothers chromosomes go into each new cell In the second division the chromosomes line up again in the center of the cell. Its a lot like mitosis. The arms of the chromosomes are pulled apart You get four gametes each with only a single set of chromosomes in it