Thank you for explaining :)Ygggdrasil said:Whether an allele is dominant or recessive depends on the exact biochemical mechanisms at work. Many times a "broken" version of a gene is recessive. For example, cystic fibrosis is caused by a mutation in an ion channel called the cystic fibrosis transmembrane conductance regulator (CFTR) that prevents the ion channel for working properly. The disease allele is recessive because one functioning allele is sufficient to make enough CFTR for the body to behave normally. Only when both copies of the gene are non-functional does the disease occur.
Some "broken" version of genes, however, will inactivate the functioning copies of the genes and thus behave as dominant alleles (these are referred to as dominant negative alleles as they are dominant alleles that cause a loss of function). This is especially common when the proteins encoded by the genes function in a complex and one broken subunit in the complex is enough to render the entire complex non-functional. Another way for an allele to be dominant is though a gain-of-function mutation, in which the allele confers its trait by performing some new function (for example, an enzyme that cannot be turned off properly). A good example is lactase persistence. Normally, humans turn off production of the enzyme required to digest lactose in milk after childhood. Mutations can "break" the body's ability to turn off the gene, leading to production of the enzymes into adulthood. Even if only one copy does not get turned off into adulthood, this is sufficient to allow lactose digestion into adulthood.
I am not so familiar with the mechanisms behind widow's peak, so I don't know specifically what is happening in that case.
Here's a particularly good explanation of the topic with more examples:
https://genetics.thetech.org/ask-a-geneticist/genotype-vs-phenotype
A dominant trait or gene is one that is expressed or visible in an individual even if only one copy of that gene is present. This means that the phenotype, or physical characteristics, of an individual will show the dominant trait even if they only inherited one copy of the gene from one parent.
A recessive trait or gene is one that is only expressed or visible in an individual if two copies of that gene are present. This means that the phenotype of an individual will only show the recessive trait if they inherited two copies of the gene, one from each parent.
Dominant and recessive traits or genes are determined by the specific alleles, or variations of a gene, that an individual inherits from their parents. Dominant alleles are represented by a capital letter, while recessive alleles are represented by a lowercase letter.
Yes, an individual can carry both a dominant and a recessive allele for the same gene. In this case, the dominant allele will be expressed in the phenotype, but the individual can still pass on the recessive allele to their offspring.
Scientists can determine if a trait or gene is dominant or recessive through experiments and observations. By studying the inheritance patterns of a particular trait or gene in different organisms, scientists can determine which allele is dominant and which is recessive. They can also use techniques such as genetic crosses and pedigree analysis to further understand the inheritance of these traits or genes.