chromosomes number is halved eg..46-->23 or 4-->2 or (2n)-->(n)
combining of genetic material from BOTH parents = VARIATION
sexual reproduction in a gamete production uses MEIOSIS
involves 2 divisions:- before the cell divides, it duplicates DNA making exact copies
In the 1st division:---- the chromosome pairs line up in the centre of the cell. The pairs are pulled apart so each new cell only has one copy of each chromosome, some fathers and some mothers going into each new cell.
In the 2nd division:---- the chormosomes line up again in the centre of the cell and the arms of the chromosomes are pulled apart = 4 gametes each with only a single set of chromosomes in
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Mitosis
ordinary cell division - ONE parent = ASEXUAL reproduction
body cells, mainly ALL cells, EXCEPT those producing gametes
preserves the chromosome number eg..46-->46 or 4-->4
each daughter cell is GENETICALLY IDENTICAL to each other and the parent cell = NO VARIATION
as the cell doesn't divide, DNA is spread out in long strings. if the cell gets a signal to divide, it duplicates its DNA so there is one copy of each cell. the DNA is copied and forms X-shaped chromosomes. Each arm of the chromosome is a duplicate of the other. The chromosomes line up in the centre of the cell, the cell fibres pull them apart and the two ends of the arm go to opposite ends ofd the cell. Membranes form around each sets of the chromosomes and these become the nuclei of two new cells..last the cytoplasm divides.
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DNA
Chromosomes are long molecules of DNA, Deoxyribose Nucleic Acid, which contains instructions to put an organism together and make it work
it is found in the nucleus of an animal and plant cell, in really long molecules called chromosomes
A gene codes for a specific protein: a gene is a section of DNA containing instructions to make specific proteins
cells make proteins by stringing amino acids together in a particular order
genes tell cells in what order to put the amino acids together
DNA determines whatr proteins the cell produces which determines what type of cell it is.
Everyone has UNIQUE DNA - only exceptions are identical twins and clones
DNA fingerprinting is a way of cutting up people's DNA into small sections and separating them. Every person's genetic fingerprint has a unique pattern.
DNA fingerprinting is used in Forensic Science taken from crime scenes and suspects, and also used in Paternity testing - see if a man is the father of a particular child
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