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Biology Revision Notes B1
B1 - You and your Genes

Genes, Chromosomes and DNA
Nearly every cell in your body has a nucleus and the nucleus contains your genetic materials.

The human cell nucleus contains 23 pairs of chromosomes, so that's 46 chromosomes in total! All of
these pairs are…

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Children get some of their alleles from each parent. This is why most children look a bit like both of
their parents. But they won't look identical to either one of their parents because they don't have all
of one of their parent's alleles, some came from the other parent.…

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b Bb Bb

b Bb Bb

They're all normal and boring because all of them are heterozygous, which causes the dominant gene
to overrule.

If two of these offspring now breed, they will produce new combinations of alleles in their kids...

B b

b Bb…

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A human genetic diagram is pretty much the same as any other one, but instead of showing alleles, it
shows sex chromosomes.



As you can see, there is a 50% chance that you could have a girl and a 50% chance that…

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Health ­ Some people are more likely to get certain diseases such as cancer through genetics, but
lifestyle can also cause it, eg. if you smoke or eat a lot of junk food, you're more likely to get ill.

Intelligence ­ One theory is that although your maximum possible IQ…

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Defective alleles are responsible for genetic disorders. Most of these defective alleles are
recessive. Cystic fibrosis is a genetic disorder of the cell membranes. It results in the body producing
a lot of thick, sticky mucus in the air passages, gut and pancreas.

The allele which causes cystic fibrosis is…

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inheriting the disorder if just one parent is a carrier. The carrier parent will be a sufferer of course as
the allele is dominant, so you could say that there aren't any carriers for Huntington's disorder as
they are all sufferers if they carry the allele. The symptoms do not…

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Gene therapy
Gene therapy could soon make it possible to cure or prevent genetic disorders. Eg. scientists can
insert a healthy copy of a gene to make up for a faulty one.

Example 1 ­ Treating cystic fibrosis
Cystic fibrosis (CF) affects about 1 in 2500 people in the UK.…

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spinal injuries and so on. To get cultures of one specific type of cell, researchers try to control the
differentiation of the stem cells by changing the environment they're growing in. So far, it's still a bit
hit and miss ­ lots more research is needed.

There are lots of…

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Another consideration is that some people think it's unfair for people to benefit from something
which is only possible because someone else has suffered or taken a risk. The trouble is, all new
medicines and medical procedures must be tested on human volunteers ­ and that always involves
some risk.…


Shreya Kochhar


Thank You So Much xxxx

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