Epistasis is when the expression of an allele of one gene masks the expression of the alleles of another. Let's use flower colour as an example. Epistasis example: flower colour In the diagram below, the flower pigment molecule begins as white. In order for the white pigment to be converted into a blue pigment, the... Continue Reading →
Autosomal Linkage and Sex Linkage – Inheritance Ep 4
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 – Inheritance Ep 3
Dihybrid inheritance looks at the possibilities of two characteristics being inherited together. Each characteristic is coded for by a separate gene. Punnett squares can be used to work out the possible genotypes and phenotypes of the offspring. In the example below, we are looking at the inheritance of wing colour in beetles as we did... Continue Reading →
Codominance and Multiple Alleles – Inheritance Ep 2
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 →
Monohybrid Inheritance – Inheritance Ep 1
A diploid organism (e.g. a human) has two alleles of 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) at a particular locus. The alleles an organism has (the genotype) will determine what characteristics it has... Continue Reading →
