contains instructions to put an organism together and make it work
found in the nulcues in long molecules called chromosomes
Gene- section of DNA contins instructions to make a specific protein by putting amino acids in order
20 amino acids used to make thousands of different protiens
DNA determines what protiens the cell produces, determines type of cell
everyone has unique DNA (execpt identical twins)
DNA fingerpriniting used for...
forensic science-crime scene
paternity testing- see if a man is the farther of a particular child
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Cell Division- Mitosis
used when plants and animals want to grow or to replace cells that have been damaged
steps:
the cell grows
the cell duplicates all 46 chromosomes and these form x-shaped chromosomes (the left arm has the same DNA as the right of the chromosome) so that it has 92 chromosomes
the chromosomes line up in the middle of the cell
cell fibres pull the arms apart
membranes form around each set of chromosomes creating a nuclei for the two cells
cytoplasm divides
two cells have the same DNA so they are identical
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Asexual Reproduction
some organisms reproduce by mitosis
e.g. strawberry plants form runners by mitosis which form into new plants which are identical to the original strawberry plant
in asexual reproduction the offspring have exactly the same gene as the parent-there is not variation
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Cell Division-Meiosis (1)
gametes- sexcells- sperm and egg cells, 23 chromosomes each
step:
sperm and egg cells combine so that you have 46 chromosomes again
chromosomes are duplicated and from x-shaped chromosomes
the male and female chromosomes bond together and cross over forming new unique chromosomes
line up in centre of cell
pulled apart by fibres
pulled apart again forming four new unique gametes
sperm made constantly by man but only one of the four new gametes becomes an egg in a woman
after two gametes join at fertilisation the cells grow repeatedly by mitosis
meiosis produces variation because their is a mixture of chromosomes from each parent
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