It’s all well and good saying “Allele, It’s in Your Genes” but the question we need to answer first is;
What are Alleles?
Alleles are different versions of the same gene.
What do they do?
Your alleles work at molecular level to determine what characteristics you have i.e. your phenotype, how your genetic and environment influences come together to create an organism’s physical appearance and behaviour. The gene for eye colour has an allele for blue colour and an allele for brown colour.
Alleles are dominant or recessive meaning the characteristics controlled by the dominant allele develops if the allele is present on one or both chromosomes in a pair. The characteristic controlled by the recessive allele develops only if the allele is present in both chromosomes in a pair. Gametes only have one allele, this is because we inherit half of our alleles from our mother and half from our father.
To produce a genetic diagram genes are represented by letters. If the two alleles are different only one can determine what characteristics is present. The allele for the characteristic that’s shown is called the dominant allele use a capitol letter for dominant alleles e.g. ‘C’. The other one is called recessive and you show these with small letters e.g. ‘c’.
Homologous Chromosomes
A pair of chromosomes carrying alleles that code for the same characteristics. If both chromosomes in a pair contain the same allele of a gene, the individual is described as being homozygous for that gene or condition. When a characteristic is determined by just one pair of alleles, as with eye colour and tongue rolling it is called monohybrid inheritance.
Most traits result not from one pair of alleles but from multiple genes interacting e.g. inheritance of blood groups in the ABO system.
Inherited Disease
Some disorders are caused by a faulty gene, which means they can be inherited. One example is polydactyly, which is caused by a dominant allele and results in extra fingers or toes. The condition is not life threatening. Cystic fibrosis, on the other hand can limit life expectancy. It causes the mucus in respiratory passage and the gut lining to be very thick, leading to build up of phlegm and difficulty in producing correct digestive enzymes. Knowing that there is a 1 in 4 chance that their child might have cystic fibrosis gives a parents the opportunity to make decisions about whether to take a risk and have a child. This is a very difficult decision to make. Technology has advanced and it is now possible to screen embryos for genetic disorders.
Best wishes,
Steve Walsh
Nutrition & Health B.A. (Hons)
Liverpool Hope University
