Revision Notes, OCR Twenty First Century Science B1

Biology 1- you and your genes! Revision notes

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Biology Revision Notes
B1- You and Your Genes
Differences in individuals are called variations
Variation can be effected by genetics and environment
Genes carry the genetic information for every living organism.
Different genes control different characteristics, e.g. eye colour
Genes come in long strips called chromosomes
Chromosomes are made of DNA and found in the nucleus of every cell in your body
DNA- Deoxyribonucleic acid
It is arranged into 2 strands, which join together to form a double helix
DNA molecules complete instructions for how an organism should be formed and
how each of its cells should function
Genes are sections of DNA; they control the development of different
They control this by issuing instructions to the cell; it carries out these instructions
by producing proteins
The proteins found inside a cell can be: structural or enzymes
Structural proteins, are for cells growth and repair
Enzymes, are used to speed up chemical reactions
All organisms have DNA- so it's possible to introduce genetic information, from one
organism to another
This will produce a new combination of genes and characteristics. This is called
genetic modification
Chromosomes usually come in pairs
Both chromosomes in the pair have the same genetic sequence
Every species is different, but humans have 23 pairs (46 in total)
The sex cells (gametes) have half the number of chromosomes
So when the 2 fuse, they have enough to make a human.
Alleles are different versions of the same gene
You inherit one allele from each parent, this is why you look similar to both of you
There are dominant and recessive alleles

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Dominant alleles controls the development of the characteristic even if you only
inherit them from one parent
Recessive alleles can only control the characteristic if you inherit them from both
Dominants are displayed by capital letters and Recessive by lower case letters
Most characteristics are determined by different genes but can also be determined
by lifestyle, and some can be affected by a combination of them both
The last pair of chromosomes in the 23 pair determines the sex of the baby
XX- Girl…read more

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If one parent is healthy and not a carrier, the disorder cannot be passed on, but if
both parents carry the disease they have a 75% chance of their child either
developing the disease or becoming a carrier
It is possible to test a person for faulty alleles
If tests show possibilities of their children getting the disorder they must decide,
whether or not they want to risk passing it on to their children
Adoption, or embryo selection are the 2 other options
Tests can…read more

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Then left to divide up till the 8 cells stage, before being screened for alleles which
cause specific genetic disorders
Any healthy embryos are implanted back into the uterus and the pregnancy goes
ahead as normal
There are concerns about this technique and how it plays nature
People believe it could lead to designer babies and this could mean certain alleles
could over time, and variation would become reduced
Gene therapy is a potential treatment for genetic disorders
It involves inserting healthy genes into cells…read more

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Then make a decisions depending on what will benefit the majority of people…read more


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