DNA and chromosomes
- Created by: Laura
- Created on: 17-04-14 10:32
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- DNA and Chromosomes
- In prokaryotic cells, such as bacteria, the DNA molecules are smaller, form a circle and are not associated with proteins. They do not have chromosomes.
- Eukaryotic cells, the DNA molecules are large, form a line rather than a circle and occur in associations with protein structures called chromosomes.
- Chromosome structure
- Chromosomes only visible when cell is dividing.
- When visible they appear as two threads, joined at a distinct point. Each thread is called a chromatid
- The DNA in chromosomes is held in place by proteins
- DNA is coiled into a double helix and the double helix is wound around the proteins to keep it in place... this forms the chromosome
- Homologous chromosomes
- Each offspring gets half the chromosomes from their mum and half from their dad. These match up to form homologous pairs
- A homologous pair is always two chromosomes that determine the same genetic characteristic but arent exactly identical
- What is an allele?
- Each gene occurs in two, occasionally more, different forms. Each of these forms is called an allele.
- Each individual inherits one allele from each parent. They may be the same of they may be different
- When they are different each allele will code for a different polypeptide
- The alleles individuals inherit may not always code for something that is necessary for them to live such as a specific enzyme.
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