Complete revision notes for Topic 17 of the CIE IGCSE Biology course: Inheritance. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Define inheritance as the transmission of genetic information from generation to generation
17.2 Chromosomes, genes and proteins
Define chromosome as a thread-like structure of DNA, carrying genetic information in the
form of genes
Define gene as a length of DNA that codes for a protein
Define allele as a version of a gene
Alleles are different versions of a particular gene.
For example, the ABO gene for blood group type has three alleles, IA, IB and IO.
Describe the inheritance of sex in humans with reference to XX and XY chromosomes
Sex is determined by an entire chromosome pair (as opposed to most other characteristics
that are just determined by one or a number of genes).
Females have the sex chromosomes XX.
Males have the sex chromosomes XY.
, The inheritance of sex can be shown using a genetic diagram (known as a Punnett square),
with the X and Y chromosomes taking the place of the alleles usually written in the boxes:
Explain that the sequence of bases in a gene is the genetic code for putting together amino
acids in the correct order to make a specific protein (knowledge of the details of nucleotide
structure is not required)
Explain that DNA controls cell function by controlling the production of proteins (some of
which are enzymes), antibodies and receptors for neurotransmitters
DNA controls cell function by controlling the production of proteins.
The proteins may be enzymes, antibodies, or receptors for neurotransmitters.
Explain how a protein is made, limited to:
The gene coding for the protein remains in the nucleus
mRNA molecules carry a copy of the gene to the cytoplasm
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