DNA and Meiosis

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  • Created on: 25-01-15 19:58
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DNA and Meiosis
Structure of DNA
DNA is the chemical that determines inherited characteristics and it contains vast amounts of
information in the form of the genetic code. DNA is made up of just three basic components that
combine to form a nucleotide.
A sugar called a deoxyribose
A phosphate group
An organic base belonging to one of two different groups:
o Single-ring bases ­ cytosine (C) and thymine (T)
o Double-ring bases ­ adenine (A) and guanine (G)
The deoxyribose sugar, phosphate group and organic base are combined as a result of
condensation reactions, to give a mononucleotide. Two mononucleotides may in turn, be
combined as a result of a condensation reaction between the deoxyribose of one mononucleotide
and the phosphate group of another. The new structure is called a dinucleotide. The continued
linking of mononucleotides in this way forms a long chain known as a polynucleotide.
DNA is made up of two long strands of nucleotides, joined together by hydrogen bonds formed
between certain bases. Adenine always pairs with thymine by means of two hydrogen bonds.
Guanine always pairs with cytosine by means of three hydrogen bonds. They are complementary
to one another.
The uprights of phosphate and deoxyribose wind around one another to form a double helix. For
each complete turn of this helix, there are ten base pairs.

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Function of DNA
DNA is the hereditary material responsible for passing genetic information from cell to cell and
generation to generation.…read more

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In eukaryotic cells, the DNA molecules are larger, form a line rather than a circle, and
occur in association with proteins to form strutures called chromosomes.
Chromosomes are only visible as distinct structures when a cell is dividing, at which time they
appear as two threads (chromatids) which join at a single point (centromere). The DNA in
chromosomes is held in position by proteins (histones). The considerable length of DNA found in
each cell is highly coiled and folded.…read more

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Each individual inherits one allele from each of its parents, which may be the
same or different.
Any differences in the base sequence of an allele of a single gene may result in a different
sequence of amino acids being coded for. This different amino acid sequence will lead to the
production of a different polypeptide, and hence a different protein.
Meiosis and genetic variation
Before the cell as a whole can divide, first the nucleus must divide, either by mitosis or
meiosis.…read more

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Locus ­ the position of a gene on a chromosome or DNA molecule
Independent segregation:
During meiosis 1, each chromosome lines up alongside its homologous partner. In humans, this
means that there will be 23 homologous pairs lying side by side, arranged randomly. One of each
pair will pass to each daughter cell. Which one of the pair goes into the daughter cell, and with
which one of any of the other pairs, depends on how the pairs are lined up in the parent cell.…read more


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