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 – 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. 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 →
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 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 →
