Genes, DNA, Chromosomes etc
- Most cells in your body have a nucleus which contains your genetic material.
- The human cell contains 23 pairs of chromosomes. They are all known and numbered.
- Chromosomes carry genes. Different genes control the development of characteristics. Example: hair colour.
- A gene is a short length of chromosome, Which is one molecule of DNA
- DNA is coiled up to form the arms of the chromosomes.
- Genes exist in different versions. Each version gives a different characteristic, like blue or brown eyes. The different versions of the same gene are call alleles.
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- Each gene is a code for making a certain protein which are the building blocks for cells. Having different versions of proteins mean that we end up with different characteristics.
- Some proteins are for structural purposes which are part of making skin, hair, blood and the cytoplasm in our cells.
- Other proteins are enzymes which control the chemical reactions in our body. Example: respiration. They also help by breaking down food molecules.
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Why are chromosomes in pairs?
Chromosomes come in pairs because we get one from each parent.
- The sex cells (the sperm and the egg) are different from the other cells in your body as they only contain 23 single chromosomes instead of 23 pairs.
- When the sperm fertilises the egg, the 23 chromosomes in the egg cell and the 23 chromosomes in the sperm cell combine.
- The fertilised egg then has 43 chromosomes (or 23 pairs) like a normal body cell.
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Why do children look a bit like their parents?
Children look like both parents but never Identical.
- Children get some alleles from each of their parents.
- Every person is unique , no one looks the same.
- There are millions of different allele combinations (about 8 million).
So no two people will look the same
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Genetic Diagrams show the chances of a child having a certain Characteristics.
- Alleles are different versions of genes.
- To represent a dominant allele we use a CAPITAL LETTER.
- To represent a recessive allele we use a little letter.
- You can either be Homozygous which means you have two alleles the same. (eg bb, BB)
- Or you can be Heterozygous which means you have two alleles that are different. (eg Bb)
- A dominant allele will always overrule a recessive allele.
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How is Gender determind?
- Gender is controlled by a certain set of chromosomes.
- All men have an X and Y chromosome (the Y causes male characteristics to develop)
- All woman have two X chromosomes (the X causes female characteristics)
This means that the Y chromosome is dominant.
- There is an equal chance of giving birth to a boy or a girl.
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