Cystic fibrosis is an inherited disorder affecting specific channel proteins in cell membranes. In this article we will look at how it is inherited, how chloride ion transport is affected, and the symptoms which develop as a consequence. Inheritance of cystic fibrosis Cystic fibrosis is an inherited recessive disorder, meaning it is caused by a... Continue Reading →
Epistasis is when the expression of an allele of one gene masks the expression of the alleles of another. The genes must code for the same characteristic in order for this to work. Let's use flower colour as an example. Epistasis example: flower colour In the diagram below, the flower pigment molecule begins as white.... Continue Reading →
Autosomal linkage and sex linkage are two cases where inheritance is very dependent on which chromosome the genes are found on. This is definitely the most difficult concept to get your head around for this topic for A-Level biology - make sure to have a good understanding of meiosis before you start. Autosomal Linkage Autosomes... Continue Reading →
Dihybrid inheritance looks at the possibilities of two characteristics being inherited together. Each characteristic is coded for by a separate gene. In this case it is much easier to use a Punnett square to work out the possible genotypes of the offspring as a genetic diagram would get very messy and difficult to read. In... Continue Reading →
In the last article we looked at inheritance of a characteristic coded for by a single gene which has one dominant allele and one recessive allele. However, sometimes alleles can be codominant or there can be more than two alleles for a gene. This increases the number of possible phenotypes. Let's look at each case... Continue Reading →
A diploid organism (e.g. a human) has two alleles for each gene in their chromosomes. Alleles are alternative forms of a gene, so an organism could have two of the same allele (homozygous) or two different alleles (heterozygous). The alleles an organism has (the genotype) will determine what characteristics it has (the phenotype). There is... Continue Reading →
In the last article we looked at natural selection, a process which leads to evolution. We saw that if an organism has advantageous alleles, it is better adapted to its environment and is more likely to survive and reproduce. In today's article we will look at the different types of adaptions that organisms can have... Continue Reading →
Natural selection is one way that evolution occurs. Evolution is the change in allele frequency over time. In this article we will look at the process of natural selection, and a few different types of selection. Note that there can be other mechanisms behind evolution as well, such as the genetic bottleneck effect described here.... Continue Reading →
Genetic diversity is defined as the number of different alleles of genes in a population. Last week we looked at one method of introducing new alleles into a population - by genetic mutation. Today we will look at other ways that genetic diversity can be increased or decreased, and how it can be measured. Increasing... Continue Reading →
