Genes encode for proteins that influence things like the immune system, skin pigmentation, hormone production, and eye color. Every human has a unique genotype, which explains the vast variety in human appearance and biology. When genes mutate, they can take on multiple forms, with each form differing slightly in the sequence of their base DNA.
These gene variants still code for the same trait i. Different versions of the same gene are called alleles. Genes can have two or more possible alleles. Individual humans have two alleles, or versions, of every gene.
Because humans have two gene variants for each gene, we are known as diploid organisms. The greater the number of potential alleles, the more diversity in a given heritable trait. An incredible number of genes and gene forms underly human genetic diversity, and they are the reason why no two people are exactly alike.
In a simplified model, we will assume that there is only one gene that encodes for eye color although there are multiple genes involved in most physical traits. Blue, green, brown, and hazel eyes are each encoded by unique alleles of said gene. When humans procreate, the child receives 23 chromosomes long strands of DNA from each parent. Each matching chromosome pair contains the same set of genes, with unique genes located at certain spots known as the gene locus.
This inheritance means that individuals have two gene copies for a given trait, one inherited from their mother and the other from their father. These are known as maternal alleles and paternal alleles. It is how these alleles interact that is responsible for unique characteristics. This results in differences between individuals such as in eye color or hair color, but it can also refer to a disease.
For instance, in cystic fibrosis, which is a very common Mendelian disorder, that disease exists only when there's a malfunction of both genes that correspond to cystic fibrosis. If there is only one mutation, then that recessive mutation can be compensated for by the normal allele. However, when the function of both are lost, then the disease manifests itself as a recessive disease where there is a loss of function and therefore observable disease.
Christopher P. Alleles are described as either dominant or recessive depending on their associated traits. Illustration to show the inheritance of dominant and recessive alleles for eye colour.
Image credit: Genome Research Limited. Genes are small sections of DNA within the genome that code for proteins. They contain the instructions for our individual characteristics — like eye and hair colour. Inheritance is the process by which genetic information is passed on from parent to child.
This is why members of the same family tend to have similar characteristics. Genetic variation is a term used to describe the variation in the DNA sequence in each of our genomes. Genetic variation is what makes us all unique, whether in terms of hair colour, skin colour or even the shape of our faces. Haemophilia A and B are two disorders characterised by slow and inefficient formation of blood clots leading to prolonged bleeding and spontaneous internal bleeding.
Single gene disorders are caused by DNA changes in one particular gene, and often have predictable inheritance patterns. If you have any other comments or suggestions, please let us know at comment yourgenome.
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