Simple genetics example. Albino rabbits have white coats and red eyes. This is due to lack of the pigment melanin Albinos are actually rather rare in the wild, but common in pet shops!
We shall consider what happens if we cross an albino rabbit with a brown rabbit.
If two of these rabbits are allowed to reproduce…
The result is:
Actually the proportion is:
3 brown : 1 albino
(as a ratio)
75% brown, 25% albino
(as a percentage)
We can also use these figures to give the chance of an individual rabbit being one colour or the other
There is a 3 in 4 (¾) or 75% chance of any baby rabbit being born brown
There is a 1 in 4 (¼) or 25% chance of any baby rabbit being born albino
In rabbits, the two colour forms are caused by 2 versions of a gene.
We say that the coat colour gene has 2 alleles: brown and albino
The brown rabbits of the F1 all have
the genotype Bb.
Their phenotype is brown because they contain a dominant allele B, and only one dominant allele is enough to give this colouration.
They have the same phenotype as their parent (brown) but a different genotype.
The white rabbits of the F2 all have
the genotype bb.
Their phenotype is white because they contain a pair of recessive alleles bb, and two recessive alleles are required to give this colouration.
They have the same phenotype as their grandparent (white) and the same genotype. Only double recessive genotypes can be forecast this way.
Because rabbits with the genotype Bb contain two different alleles they are called heterozygous, whereas rabbits with the genotype BB and bb are both called homozygous or true-breeding.
In heterozygous brown rabbits the recessive allele b is hidden, but it could reappear in the next generation…….