Chromosomes, Genes & Proteins (Cambridge (CIE) IGCSE Biology)
Revision Note
Written by: Phil
Reviewed by: Lára Marie McIvor
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The Structure of Genes
Inheritance of Chromosomes, Genes and DNA
Inheritance is the transmission of genetic information from generation to generation
Chromosomes are located in the nucleus of cells
They are thread-like structures of DNA, carrying genetic information in the form of genes
A gene is a short length of DNA found on a chromosome that codes for a specific protein
This could be a structural protein such as collagen found in skin cells, an enzyme or a hormone
Genes control our characteristics as they code for proteins that play important roles in what our cells do
Think about zooming into the nucleus of a cell, as shown in the diagram below
On the right is the zoomed-out view
Which zooms in as we read across the diagram right-to-left
Genes are short lengths of DNA that code for a protein. They are found on chromosomes
Alleles are different versions of a particular gene. The ABO gene for blood group type has three alleles, IA, IB and IO
Alleles give all organisms their characteristics
Examiner Tips and Tricks
The Zoom model is always useful when trying to viualise where you are in a cell, and what molecules are doing what. Imagine a zoom lens that has the power to zoom right out to look at a whole organism, but also to zoom right into individual molecules. This helps in recognising the structures in cell nuclei visible as chromosomes, then zooming in to picture the individual genes and then, the bases that make up the DNA
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